COMMENTARY ON ARISTOTLE’S
DE ANIMA

ST. THOMAS’S COMMENTARY

LECTIO ONE

§ 1. in studying any class of things, it is first of all necessary, as the Philosopher says in the De Animalibus [I, 5], to consider separately what is common to the class as a whole, and afterwards what is proper to particular members of the class. Such is Aristotle’s method in First Philosophy; for at the beginning of the Metaphysics he investigates the common properties of being as such, and only then does he go on to the particular kinds of being. The reason for this procedure is that it saves frequent repetition.

Now living beings taken all together form a certain class of being; hence in studying them the first thing to do is to consider what living things have in common, and afterwards what each has peculiar to itself. What they have in common is a life-principle or soul; in this they are all alike. In conveying knowledge, therefore, about living things one must first convey it about the soul as that which is common to them all. Thus when Aristotle sets out to treat of living things, he begins with the soul; after which, in subsequent books, he defines the properties of particular living beings.

§ 2. In the present treatise on the soul we find, first, an Introduction: in which the author does the three things that should be done in any Introduction. For in writing an Introduction one has three objects in view: first, to gain the reader’s good will; secondly, to dispose him to learn; thirdly, to win his attention. The first object one achieves by showing the reader the value of the knowledge in question; the second by explaining the plan and divisions of the treatise; the third by warning him of its difficulties. And all this Aristotle does here. First, he points out the high value of the science he is introducing. Secondly, at ‘We seek then,’ he explains the plan of the treatise. Thirdly, at ‘To ascertain anything reliable’ he warns of its difficulty. Under the first point he explains, first the dignity of this science, and then, at ‘Indeed, an acquaintance,’ its utility.

§ 3. As regards, then, the said dignity we should note that, while all knowledge is good and even honourable, one science can surpass another in this respect. All knowledge is obviously good because the good of anything is that which belongs to the fulness of being which all things seek after and desire; and man as man reaches fulness of being through knowledge. Now of good things some are just valuable, namely, those which are useful in view of some end—as we value a good horse because it runs well; whilst other good things are also honourable: namely, those that exist for their own sake; for we give honour to ends, not means. Of the sciences some are practical, others speculative; the difference being that the former are for the sake of some work to be done, while the latter arc for their own sake. The speculative sciences are therefore honourable as well as good, but the practical are only valuable. Every speculative science is both good and honourable.

§ 4. Yet even among the speculative sciences there are degrees of goodness and honourableness. Every science is valued first of all as a kind of activity, and the worth of any activity is reckoned in two ways: from its object and from its mode or quality. Thus building is a better activity than bed-making because its object is better. But where the activities are the same in kind, and result in the same thing, the quality ‘alone makes a difference; if a building is better built it will be a better building. Considering then science, or its activity, from the point of view of the object, that science is nobler which is concerned with better and nobler things; but from the point of view of mode or quality, the nobler science is that which is more certain. One science, then, is reckoned nobler than another, either because it concerns better and nobler objects or because it is more certain.

§ 5. Now there is this difference between sciences, that some excel in certainty and yet are concerned with inferior objects, while others with higher and better objects are nevertheless less certain. All the same, that science is the better which is about things; because, as the Philosopher observes in Book XI of the De Animalibus, we have a greater desire for even a little knowledge of noble and exalted things—even for a conjectural and probable sort of knowledge—than for a great and certain knowledge of inferior things. For the former is noble in itself and essential, but the latter only through its quality or mode.

§ 6. Now this science of the soul has both merits. It has certainty; for everyone knows by experience that he has a soul which is his life-principle. Also it has a high degree of nobility; for among lower things the soul has a special nobility. This is what Aristotle means here when he says, ‘Holding as we do that knowledge’, i.e. speculative science, ‘is good and honourable.’ And one science is better and nobler than another in two ways: either, as we have seen, because it is more certain—hence he says ‘more certain’,—or because it is about ‘more excellent’ things, i.e. things that are good in themselves, and ‘more wonderful things’, i.e. things whose cause is unknown. ‘For both these reasons’, he goes on to say, ‘we give a primary place to an enquiry about the soul’. He uses the term ‘enquiry’ because he is going to discuss the soul in a general way, without attempting, in this treatise, a thorough examination of all its properties. As to the words ‘a primary place’, if they are taken as applying to the whole of Natural Science, then they refer to superiority in dignity and not to priority in order; but if they refer to the science of living things only, they mean priority of order.

§ 7. Then, with ‘Indeed an acquaintance etc.,’ he gains the reader’s good will by showing the utility of this science. Some knowledge of the soul he says, would seem to be very useful in all the other sciences. it can be of considerable service to philosophy in general. In First Philosophy it is impossible to attain knowledge of the divine and highest causes except through what we can acquire by actualising our intellectual power; and if we knew nothing about the nature of this power we should know nothing about the immaterial substances, as the Commentator remarks à propos of Book XI of the Metaphysics. Again, as regards Moral Philosophy. We cannot master the science of morals unless we know the powers of the soul; thus in the Ethics the Philosopher assigns the virtues to the different powers. So, too, it is useful for the Natural Scientist, because many of the things he studies are animate things, all of whose movements originate in the soul: ‘for it is,’ says Aristotle, ‘as it were, the principle of living things’: the phrase ‘as it were’ does not express a comparison; it is descriptive.

§ 8. Next, at ‘We seek then’, he states the plan of his treatise, saying that we are ‘to consider’, i.e. by way of outward symptoms, and ‘to understand’, i.e. by way of demonstration, what the soul really is in its nature and essence; and then whatever qualities belong to it or affect it. But in the latter a diversity appears: for while some of the soul’s modifications, such as understanding and speculative knowledge, seem to belong to the soul of and in itself, others, such as pleasure and pain, the senses and imagination, though they depend on some soul or other, seem to be common to all animals.

§ 9. Then at ‘To ascertain’, he introduces the difficulty of this study; and this from two points of view. It is hard, first, to know the essence of the soul, and secondly to know its accidents or characteristic qualities. As to the essence, there is a double difficulty: first, as to how it ought to be defined, and then as to the elements of the definition (this point comes at ‘Perhaps the first thing needed’).

He remarks, therefore, that while knowledge of the soul would be valuable, it is not easy to know just what the soul is. Now this is a difficulty in studying anything; for the question about substance and essence is common to the study of soul and of many other things; the first difficulty being that we do not know what method to use; for some say we should use deductive demonstration, others the method of elimination, others one of comparison. Aristotle himself preferred the method of comparison.

§ 10. The second difficulty concerns the elements of the definition. A definition manifests a thing’s essence; and this cannot be grasped apart from the principles on which it depends. But different things have different principles, and it is hard to see which principle is involved in any particular thing. Hence, in formulating or seeking for a definition of soul we encounter three main difficulties: (a) concerning its essence; (b) concerning its parts; (c) concerning that necessary contribution to a definition which comes from knowing the soul’s accidental qualities.

§ 11. As regards the essence of soul, there is a doubt about that which is the first thing to be looked for in defining anything, i.e. the genus to which it belongs. What is the genus of soul? Is it a substance or a quantity or a quality? And not only must we decide upon the ultimate genus, but also on the proximate one; thus we do not define man as a substance, but as an animal. And if soul is found to belong to the genus of substance we shall still have to decide whether it is actual or potential substance, since every genus can be regarded both as potential and as actual. Also, since substances are either composite or simple, we shall have to ask which is one or the other and whether it is divisible or indivisible. There is also the question whether all souls are of the same species or not; and if they are not, whether they are generically different or not. Again there is uncertainty as to what is to be included in the definition, some things being defined in terms of genus, some as species; hence the question whether we should define soul in terms of genus or as the specification of a species.,

§ 12. For some enquirers seem to have in view only the human soul. Among the earlier philosophers there were two opinions about soul. The Platonists, holding that universals existed separately as the Forms or Ideas that caused knowledge and being in individual things, maintained that there was a Soul-in-Itself which was the cause aud ‘idea’ of particular souls and from which all that we find in these drew its origin. On the other hand were the Natural Philosophers who maintained that no universal substances existed in the real world, that the only real things were individuals. And this raises the question for us, whether we, like the Platonists, ought to look for one common idea of Soul; or rather, as the Natural Philosophers said, study this or that particular soul, e.g. of horse or man, or god. He says ‘or god’ because at that time men believed that the heavenly bodies were gods, and that they were alive.

§ 13. However, Aristotle chose to seek a definition of both—of Soul in general and of each kind of soul. But when he says, on this point, that ‘animal as universal is nothing real, or is secondary’, we must understand that one can speak of a ‘universal animal’ in two ways: either as universal, i.e. as one nature existing in, or predicated of, many individuals; or as animal. And both these aspects can be regarded either in relation to existence in the real world or as existing in the mind. As regards existence in the real, world, Plato held that the universal animal did so exist and existed prior to particular animals; because, as has been said, he thought that there were universals and ideas with an independent existence. Aristotle, however, said that the universal as such had no real existence, and that if it was anything at all it came after the individual thing. But if we regard the nature of animals from a different point of view, i.e. not as a universal, then it is indeed something real, and it precedes the individual animal as the potential precedes the actual.

§ 14. Then, at ‘Further, if there are not many’, Aristotle touches on the difficulties that arise concerning the soul’s potentialities. For, in, the soul are ‘parts’ that exist as potencies: the intellectual and sensitive and vegetative ‘parts’. The question is whether these are different souls, as the Platonists liked to think (and even maintained), or are only potencies in the soul. And if they are potencies, we must further decide whether to enquire first into the potencies themselves, and then into their acts, or into the acts first and then the potencies—e.g. into the act of understanding before the intellect. And if we take the acts first, there is still the question whether the objects of these acts should be studied before the faculties, e.g. the sense-object before the sense-faculty or the thing understood before the understanding.

§ 15. Next, at ‘Now it seems’, he states the difficulties that arise with regard to those accidental qualities which contribute to a definition of the soul. These are relevant here because a definition ought to reveal a thing’s accidental qualities, as well as its essential principles. If indeed the latter could be known and correctly defined there would be no need, to define the former; but since the essential principles of things are hidden from us we are compelled to make use of accidental differences as indications of what is essential. Thus to be two-footed is not of the essence of anything, yet it helps to indicate an essence. By such accidental differences we are led towards knowledge of the essential ones. It would indeed be easier to grasp even What is accidental to the soul if we could only first understand its essence, just, as in mathematics, it is a great help towards understanding that the angles of a triangle are equal to (two) right angles to know first what is meant by straight, curved and plane. Hence the difficulty of our present position. On the other hand a prior examination of the accidental factors is a considerable help towards knowing the essence, as has been said. if, therefore, one were to propose a definition from which no knowledge of the accidental attributes of the defined thing could be derived, such a definition would not be real, but abstract and hypothetical. But one from which a knowledge of the accidents flows is a real definition, based on what is proper and essential to the thing.

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403a 2-403 b 23

BOOK I, CHAPTER, I, CONTINUED

INTRODUCTION CONTINUED

QUESTIONS OF METHOD

The modifications of the soul present a problem: are they all shared by what has soul, or are some proper to the soul alone? § 16

It is necessary indeed, but not easy, to deal with this problem. For in most cases there is, apparently, no action or being acted on without the body; as in anger, desire, confidence, and sensation in general. Understanding however would seem especially proper to the soul. Yet if this too is a sort of imagination, or never occurs without it, not even this exists, in fact, apart from the body. § 17-20

But if the soul has some operation or affection exclusive to itself, then it could exist as a separate entity. If, however, there is nothing thus proper to it, then it is not separable, but is like a straight line, which has, as such, many properties—such as being able to touch a bronze sphere at a given point; but straightness separated does not touch it; not being in fact separable, since it is always with a bodily subject. § 21

Now all the soul’s modifications do seem to involve the body—anger, meekness, fear, compassion, and joy and love and hate. For along with these the body also is to some degree affected. An indication of this is that sometimes violent and unmistakable occurrences arouse no excitement or alarm; while at other times one is moved by slight and trifling matters, when the physical system is stimulated to the condition appropriate to anger. This is still more evident fearful being present, feelings occur as in one when, nothing who is frightened. If this is the case, it is evident that the passions are material principles; hence such terms as ‘becoming angry’ mean a motion of such and such a body, or of a part or power proceeding from and existing for the body. § 22

For this reason, therefore, the natural scientist ought to examine the soul, either all kinds, or this kind. § 23

The natural scientist and the dialectician will define each of those modifications differently. Take the question, what is anger? The latter will say, a desire for retaliation, or something similar; the former, an effervescence of blood or heat about the heart. Of these, the natural scientist designates the matter, the dialectician, the form or idea. For this ‘idea’ is the thing’s form. This however must have existence in material of the sort in question; if it is a house, one formula will be, ‘a covering to prevent destruction from wind and rain and excessive heat’; the other, ‘stones and beams and timber’; another, ‘the form; in these materials; for those reasons. Which is the physical definition? That which states the matter ans ignores the idea? Or that which states. the idea only?

Or rather, the compound of both? What then of the other two? Now there is no one who deals with inseparable qualities of matter, precisely as inseparable from it; but he who is concerned with the affections and activities of the special matter of this or that body is the natural scientist; whereas whatever things are not specifically such, another considers; in certain matters it may perchance be a technical expert, a carpenter or physician. Concerning however what is inseparable from matter, and yet as not involved in the specific qualities of this or that body, but abstracted from any, the mathematician; and concerning what is separable, the ‘first philosopher’. § 24-9

To return from our digression. We were saying that the passions, of the soul are not separable from the physical material of animals (anger and fear having this kind of existence), and yet also that they differ, in this, from the line and the surface.

CHAPTER II

Investigating the soul, it is necessary, while suspending judgment on matters which should be held uncertain, that we study the opinions of certain thinkers who have dealt with the subject, so as to take note of anything they said pertinently, whilst avoiding their mistakes. § 30

ST. THOMAS’S COMMENTARY

LECTIO TWO

§ 16. Having stated the difficulty of this science in respect of the problem of the soul’s substance and essence, the Philosopher proceeds to the problem of its modifications and accidental qualities. And here he does two things: he states, first, and solves a difficulty concerning the soul’s modifications; and then, using this solution, ‘he shows that knowledge of the soul pertains to natural science or ‘physics’, where he says, ‘For this reason, therefore, the natural scientist’. As to the first point, he says it is a problem whether the soul’s modifications and activities belong to it independently of the body, as Plato thought, or are none of them peculiar to the soul, being all shared by soul and body together.

§ 17. Going on at ‘It is necessary,’ he again does two things. First he shows the difficulty of the question, and then, at ‘But if the Soul,’ the necessity of putting it. He begins then by observing that we cannot avoid the question whether the soul’s modes and activities ire proper to it or shared by the body, and that this is not an easy question but a very difficult one. The difficulty, as he explains, arises from the fact that many activities seem to be common to soul and body and to require the body, for instance, getting angry and having sensations and so on; which all involve body as well as soul. If there is anything peculiar to the soul it would appear to be the intellectual activity or understanding; this seems to belong to the soul in a special way.

§ 18. And yet, on closer consideration, even understanding would not seem to pertain to the soul alone. For either it is the same as imagination, as the Platonists thought, or it does not occur without the use of imagination (for there used to be men, such as the early natural philosophers, who said that intellect in no way differed from the senses, which would imply that it does not differ from the imagination; as indeed the Platonists were led to say). As, then, imagination presupposes the body and depends on it, they said that understanding was common to soul and body together, rather than the work of the soul alone. And even granted that intellect and imagination are not identical, still the one cannot function without the other. It would follow that understanding is not of the soul alone, since imagining presupposes the body. Understanding then, it seems, does not occur where there is no body.

§ 19. Now although Aristotle clears up this problem in Book III, we shall say something about it here. Understanding, then, is in one sense, proper to the soul alone, and in another sense common to both soul and body. For it should be realised that certain activities or modifications of the soul depend on the body both as an instrument and as an object. Sight, for instance, needs a body as object—because its object is colour, which is only found in bodies;—and also as an instrument—because, while the act of seeing involves the soul, it cannot occur except through the instrumentality of a visual organ, the pupil of the eye. Sight then is the act of the organ as well as of the soul. But there is one activity which only depends on the body to provide its object, not its instrument; for understanding is not accomplished with a bodily organ, though it does bear on a bodily object; because, as will be shown later, in Book III, the phantasms in the imagination are to the intellect as colours to sight: as colours provide sight with its object, so do the phantasms serve the intellect. Since then there cannot be phantasms without a body, it seems that understanding presupposes a body-not, however, as its instrument, but simply as its object.

§ 20. Two things follow from this. (1) Understanding is an act proper to the soul alone, needing the body, as was said above, only to provide its object; whereas seeing and various other functions involve the compound of soul and body together. (2) Whatever operates of itself independently, has also an independent being and subsistence of its own; which is not the case where the operation is not independent. Intellect then is a self-subsistent actuality, whereas the other faculties are actualities existing in matter. And the difficulty in dealing with this type of question arises simply from the fact that all functions of the soul seem at first sight to be also functions of the body.

§ 21. After this, when Aristotle says ‘But if the soul’, he states a reason for putting this question, namely, that on its answer depends the answer to a question that everyone asks very eagerly about the soul: whether it can be separated from the body. So he says that if the soul has any function proper to itself it can certainly be separated, because, as was pointed out above, whatever can operate on ,its own can exist on its own. Conversely, if the soul had no such proper function it would not be separable from the body; it would be in the same case as a straight line—for though many things can happen to a straight line qua straight line, such as touching a brass sphere at a certain point, still they can only come about in a material way: a straight line cannot touch a brass sphere at any point except materially. So also with the soul; if it has no activity proper to itself, then, however many things affect it, they win do so only in a material way.

§ 22. Next, when he says ‘Now all the soul’s,’ he draws out what had been presupposed above, namely that certain modifications affect soul and body together, not the soul alone. And this he shows by one argument in two parts; which runs as follows. Whenever the physical constitution of the body contributes to a vital activity, the latter pertains to the body as well as the soul; but this happens in the case of all the ‘modifications’ of the soul, such as anger, meekness, fear, confidence, pity and so forth, hence all these ‘modifications’ would seem to belong partly to the body. And to show that the physical constitution plays a part in them he uses two arguments. (1) We sometimes see a man beset by obvious and severe afflictions without being provoked or frightened, whereas when he is already excited by violent passions arising from his bodily disposition, he is disturbed by mere trifles and behaves as though he were really angry. (2) At ‘This is still more evident:’ what makes this point even clearer is that we see in some people, even when there is no danger present, passions arising that resemble one such ‘modification’ of the soul; for instance melancholy people, simply as a result of their physical state, are often timid when there is no real cause to be. Obviously then, if the bodily constitution has this effect on the passions, the latter must be ‘material principles’, i.e. must exist in matter. This is why ‘such terms,’ i.e. the definitions of these passions, are not to be predicated without reference to matter; so that if anger is being defined, let it be called a movement ‘of some body’ such as the heart, or ‘of some part or power’ of the body. Saying this he refers to the subject or material cause of the passion; whereas ‘proceeding from’ refers to the efficient cause; and ‘existing for’ to the final cause.

§ 23. Then at ‘For this reason,’ he concludes from the foregoing that the study of the soul pertains to natural science—a conclusion following from the way the soul is defined. So he does two things here: (1) he proves his statement; (2) he pursues his discussion of definitions, where he says ‘the natural scientist and the dialectician’. The proof of his statement runs thus. Activities and dispositions of the soul are also activities and dispositions of the body, as has been shown. But the definition of any disposition must include that which is disposed; for its subject always falls within the definition of a disposition. If, then, dispositions of this kind are in the body as well as in the soul, the former must be included in their definition. And since everything bodily or material falls within the scope of natural science, so also must the dispositions of which we speak. Moreover, since the subject of any dispositions enters into the study of them, it must be the task of the natural scientist to study the soul—either absolutely ‘all’ souls, or ‘of this kind’, i.e. the soul that is joined to a body. He adds this because he has left it uncertain whether intellect is joined to the body.

§ 24. Where he says ‘The natural scientist and the dialectician,’ he continues his discussion of definitions. Explaining that, while some definitions of the dispositions of the soul include matter and the body, others exclude matter and refer only to the form, he shows that the latter kind of definition is inadequate. This leads him to go into the difference between these types of definition. Sometimes the body is omitted, as when anger is defined as a desire of revenge; and sometimes the bodily or material factor is included, as when anger is called a heating of blood round the heart. The former is a logical definition, but the latter is physical, since it includes a material factor, and so pertains to the natural scientist. The natural scientist points to the material factor when he says that anger is a heating of blood round the heart; whereas the dialectician points to the species or formal principle; since to call anger a desire of revenge is to state its formal principle.

§ 25. Now the first type of definition is obviously inadequate. The definition of any form existing in a particular matter must take account of the matter. This form, ‘the desire for retaliation’, exists in a definite matter, and if the matter is not included, the definition is clearly inadequate. The definition, then, must state that this thing, i.e. the form, has being in this particular sort of matter.

§ 26. Thus we have three kinds of definition. The first states the species and specific principle of a thing, and is purely formal—as if one were to define a house as a shelter from wind, rain and heat. The second kind indicates the matter, as when a house is called a shelter made of stones and beams and wood. But the third kind includes in the definition ‘both’, namely matter and form, calling a house a particular kind of shelter, built of particular materials, for a particular purpose—to keep out the wind, etc. So he says that ‘another’ definition has three elements: the material, ‘in these’, i.e. beams and stones; the formal,”the form’; and the final, ‘for those reasons’, i.e. to keep out the wind. So matter is included when he says ‘in these’. form when he says ‘form’. and the final cause when he says ‘for those reasons’. All three are needed for a perfect definition.

§ 27. To the question which of these types of definition pertains to the natural scientist, I answer that the purely formal one is not physical but logical. That which includes matter but omits the form pertains to no one but the natural scientist, because only he is concerned with matter. Yet that which includes both factors is also in a special way the natural scientist’s. Thus two of these definitions pertain to natural science, but of the two the merely material one is imperfect, while the other, that includes the form also, is perfect. For only the natural scientist studies the inseparable dispositions of matter.

§ 28. But there are various ways of studying the dispositions of matter, as Aristotle now proceeds to show. He divides the students of these dispositions into three classes. One class consists of those who, while they study material dispositions, differ from the natural scientist in their point of view; thus the craftsman differs from the scientist in that he starts from the point of view of art, but the natural scientist from that of real nature. Another class consists of those who, though they consider forms that exist in sense-perceptible matter, do not include such matter in their definitions. The forms referred to are such as curved, straight, and so on, which, though they exist in matter and are, in fact, inseparable from it, are not, by the mathematician, regarded under their sense-perceptible aspect. The reason is that if it is through its quality that a thing is sense-perceptible, quality presupposes quantity; hence the mathematician abstracts from this or that particular material factor in order to attend exclusively to the purely quantitative. Finally, the third class studies things whose existence is either completely independent of matter or can be found without matter. This is First Philosophy.

§ 29. Note that this division of Philosophy is entirely based on definition and the method of defining. The reason is that definition is the principle of demonstration. Since things are defined by their essential principles, diverse definitions reveal a diversity of essential principles; and this implies a diversity of sciences.

§ 30. Then at ‘To return,” he comes back to the matter in hand after the apparent digression about definitions. The point under discussion was that such modifications of the soul as love, fear and so forth are inseparable from physical animal matter inasmuch as they have this sort of existence, i.e. as passions in the body; in which they differ from lines, plane-surfaces and so on, which can be considered by the mind apart from the matter that they naturally imply. If this is the case then the study of such dispositions, and even of the soul itself, becomes, as has been said, the affair of the natural scientist.

And ‘concerning this’ i.e. the soul, we must, at our present stage, take account of the opinions of the ancients no matter who they were, provided they had anything to say about it. This win be useful in two ways. First, we shall profit by what is sound in their views. Secondly, we shall be put on our guard against their errors.

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403b24–404b7

BOOK I, CHAPTER II, CONTINUED

PREVIOUS THEORIES

DEMOCRITUS, THE PYTHAGOREANS, ANAXAGORAS

Our enquiry must begin with a statement of what seems most to belong by nature to the soul. The animated being would appear to differ from the inanimate in two primary respects: by motion and by sense-perception. And these two notions are roughly what our predecessors have handed down to us concerning the soul. § 31-2

For some say that the soul is principally and primarily what moves. Holding that what does not itself move moves no other moving thing, they thought that the soul too was thus. § 33

Hence Democritus, said it was a kind of fire or heat. There exist an infinite number of shapes and atoms, and those of the spherical kind are, he said, fire and soul: like the dust-motes in the air called ‘atomies’ seen in the rays of the sun in doorways; and of all the seeds of these, he said, are the elements of all Nature. Leucippus had a similar opinion. Those round in shape make the soul, because they are most able to penetrate everywhere, and since they move of themselves, they have also the power to move everything else. The soul, they maintained, is what causes movement in living things: and accordingly breathing is coterminous with living. That which envelops all bodies expels by compression the atoms [within], thus causing movement in animals, for these [atoms] are never at rest. A reinforcement must come therefore [he said] from without; in that other atoms enter by respiration, preventing from dispersal those that are within the animate body, and which simultaneously resist the constraining and compressing environment; and that animals live so long as they can do this. § 34-5

The teaching of the Pythagoreans seems to have had much the same purport. Some of these said the soul consisted of atoms in the air; others, that it was what sets these in motion. And these atoms are mentioned. because they seem to be always moving, even if the soul be quite tranquil. § 36

All who say that the soul is a thing that moves itself tend in the same direction; all seem to hold that movement is what is most proper to the soul, and accordingly that all things are in motion on account of the soul, but the soul itself on its own account; because one sees nothing moving other things that is not itself moving. § 37

Anaxagoras likewise said that the soul is a mover, as also did anyone else who held that a Mind moves all things. But his view is not exactly Democritus’. § 38

He [Democritus], asserts that intellect and soul are absolutely identical; and that what appears is the truth. And therefore that Homer aptly says of Hector that he lay ‘other-minded’. He does not use the term intellect to denote a definite faculty concerned with truth, but identifies soul and intellect. § 39

Anaxagoras is less definite about these matters. He often says that the cause of being right or good is intellect, and that this is the soul. For it is, he says, in all animals, great and small, noble and base. § 40

It does not seem, however, that there exists mind, in the sense of prudence, alike in all animals: nor even in all men. § 41

All those therefore who have regarded life from the point of view of movement have held soul to be pre-eminently a moving force. § 42

ST. THOMAS’S COMMENTARY

LECTIO THREE

§ 31. So much by way of Introduction. The Philosopher has stated his aim in general and the difficulty of the undertaking; which he now proceeds to carry out in the order already indicated. The whole treatise divides into two parts. In the first the soul’s nature is discussed as other philosophers have regarded it; but in the second as it is in reality. The latter section begins at Book II. The first part itself has two parts. The former simply relates the opinions of other philosophers; the second, beginning at ‘The first thing to be considered,’examines them. The former part itself divides into two parts, in the first of which Aristotle distinguishes

between the starting points of the other philosophers, while in the second, starting at ‘For some say’, he shows how they severally came to hold their different opinions.

§ 32. First of all then he says that one ought to start by gathering together everything that would seem to belong to the soul by nature. As to this, we should note that when we find things differing both by clear and understandable differences and by differences that are still obscure, we must assuredly take the former as a means to arrive at knowledge of the latter. This was the method used by the philosophers in their study of the soul. Living things differ from non-living in having ‘souls’; but because the nature of the soul was not evident and could not be investigated except by way of certain more obvious notes which differentiate animate from inanimate things, the philosophers first took these more evident characteristics and tried, through them, to come to knowledge of the soul’s nature. These evident notes are two: sensation and movement. Animate things seem to be characterised chiefly by movement, in that they move themselves, and by having sense awareness or perception. So the ancients thought that if they could discover the principle of these two factors they would know the soul; hence their efforts to discern the cause of movement and sensation. They all agreed in identifying the soul with the cause of movement and sense-perception. But just at this point also their differences began; for some tried to arrive at the soul by way of movement, and others by way of sense-perception.

§ 33. Hence at ‘For some say’ he states these differences: taking those of his predecessors first who started their enquiry from movement; and then, at ‘All who have considered’, those who started from knowledge; and thirdly, at ‘But since the soul’, those who started from both. With regard to the first group we should note that it had one principle in common, namely, that if living things are moving things, the soul must be both moving and moved. They assumed this because they, thought that one thing could only move another if it were itself already moved; that is, only what is moved moves. So if living things are moved, by the soul, then clearly the soul itself, and preeminently, must be moved. It was this that led the early students of Nature to class the soul among things that are moved. But about this also different opinions arose.

§ 34. When therefore he says, ‘Hence Democritus’, Aristotle states first of all the view of Democritus, one of the early philosophers, who, thinking that the soul by nature was in a state of maximum movement, which state seems natural to fire, maintained that the soul ‘was a kind of fire or heat’. Such was his view. For he did not admit the existence of anything in Nature except what is sense-perceptible and corporeal; and the first principles, he said, of all things are indivisible bodies, infinite in number, which he called atoms. These atoms, he said, are all the same by nature, differing from each other only in shape, position and arrangement (though here only the difference of shape is alluded to, as being the only necessary one. This consists in some being round, some square, some pyramids, and so on). He also maintained that the atoms were mobile and never ceased moving, and that the world had come into being through their fortuitous coming together. And to illustrate the mobility of these bodies he took the example of the particles that move in the air even when no wind blows, as we can see when a sunbeam shines through a doorway. Since the atoms, being indivisible, are much smaller than such particles, they must obviously be extremely mobile. And because the spherical is, of all shapes, the one best suited for movement—having no angles to impede it,—and since the soul, as the cause of movement in living was thought to have maximum mobility, Democritus concluded that among these infinitely numerous bodies the spherical ones were the soul.

135. Leucippus, a companion of Democritus, held the same opinion. And Democritus thought the following was a sign of its truth. He maintained that ‘coterminous with’, or essential to, life is respiration (a short-sighted view since not all living things breathe), and that respiration is necessary because the body is full of small ever-moving spherical particles (the cause, as he thought, of all movement in animal bodies) and that the surrounding air compresses what it ‘envelops’, i.e. our bodies, and ‘expels’, i.e. thrusts out of them, those particles which are so shaped as to impart movement to animals, being never at rest themselves. Lest, therefore, our bodies should decay with the loss of all these particles, he said that respiration is necessary whereby fresh particles may be brought in, and those already within prevented from leaving by those that inhaling brings in. And he said that animals can live as long as they can do this, i.e. as long as they can breathe. The point of the argument is that if breathing is called the cause of life because it keeps the spherical particles inside the animal body, and also introduces fresh ones lest the body should decay through loss of particles by movement, then it is clearly implied that the particles ate the soul itself. They are indeed the same particles that Democritus said were fiery by nature and the cause of heat.

§ 36. Next, at ‘The teaching of the Pythagoreans,’ Aristotle mentions a view of certain Pythagoreans which resembles that of Democritus; for their statement and his seem to mean the same’ although the Pythagoreans themselves do not all agree. Some of them, agreeing with Democritus, said that motes in the air, i.e. indivisible, infinitely numerous particles, were the soul. Others, however, of the same school, said that the soul was rather the force that moved those particles. Of this opinion was a certain Archelaus, the master of Socrates, as Augustine remarks in the De Civitate Dei [VIII, 2]. The reason why the soul has been thus identified with these particles has been already given—namely, that as the soul was regarded as being especially mobile, and as those particles seem to be always moving (even when the air is calm) they identified the one with the other.

§ 37. Then, at ‘All who say,’ he summarises the views of a number of philosophers, saying that all who have defined the soul in terms of movement and called it that which moves itself, ‘tend in the same direction’, i.e. the same as those mentioned already. All these, it seems, agreed -in thinking that the soul’s first and chief characteristic was movement; all things being moved by soul, and soul by itself. The reason for this was, as has been noted, that they all thought that only what was itself in motion could move other things. Since the soul moves other things, they thought the soul especially and principally was in motion.

§ 38. In the third place, at ‘Anaxagoras likewise’, he states the view of Anaxagoras. He first shows how this philosopher agrees with those already mentioned, saying that he, and anyone else who held that Intellect moved all things, really agreed with them that the source of all movement was a soul. Anaxagoras, however, differed in this that he denied that every mover was itself in motion, and maintained the existence of a pure and transcendent Intellect which, motionless itself, moved all other things; and that the soul was of this nature too. (This view led some into the error of divinising the soul.) Thus Anaxagoras agreed with the other philosophers in calling the soul a principle of movement, but disagreed with them in saying that it was not itself moved (for they said the contrary). And he also differed from Democritus in what he understood by intellect.

§ 39. When Aristotle therefore says ‘He (i.e. Democritus) asserts’, he states this last difference, first stating Democritus’ opinion that intellect and soul were ‘absolutely’, i.e. everywhere and in all respects, the same. Democritus said this because he held that only sense-perceptible things existed in the real world, and that no cognitive faculty existed in the soul except sensitivity. From this he inferred that no definite truth about things was attainable, that nothing could be definitely known with certainty: truth being simply what appears to be true; and what one man thought about anything being never any nearer the truth than what another man thought about the same thing at the same time. in consequence he maintained that contradictories were both true at the same time; and this because, as we have said, he took intellect to be, not the faculty for knowing truth and understanding intelligible objects, but a mere sense-faculty. Only the sensible, he thought, could be known, since only the sensible existed. And because the latter is continually changing there could be no certain truth about anything. Never attaining to an understanding of the intellect as the supreme faculty ‘concerned with truth’, i.e. which bears on true being, and admitting only the faculties of sense, he completely ‘identifies soul and intellect’. The intellect changed, he said, as the whole man changed. Hence his approval of Homer’s Phrase ‘Hector lies other-minded’, i.e. Hector’s mind was altered by Hector’s condition; for he thought one thing as conqueror, another as conquered.

§ 40. Next, at ‘Anaxagoras is less definite’, he shows how Anaxagoras differed from Democritus, first stating the former’s opinion and then, at ‘it does not seem’, criticising it. First then he observes that Anaxagoras spoke with less certainty and less conclusively about the soul. He often said that intelligence was the cause of right actions, whilst elsewhere he also identifies intelligence with the soul; for it is agreed that a soul is found in all animals, the lower as well as the higher, the smaller as well as the larger; and Anaxagoras said that intelligence was in all of them. Clearly then he identifies soul and intelligence.

§ 41. Secondly, at ‘It does not seem’, he shows the inconsistency of Anaxagoras’ use of the term intellect. For sometimes Anaxagoras distinguishes between soul and intellect, but sometimes also he identifies them. These are contradictory statements which cannot both be true; as Aristotle proceeds to show. Right action, he says, admittedly derives from intellect perfected by prudence. If then the intellect that causes right action is the same thing as the soul, it follows that intellect perfected by prudence is the same as the soul. But this is false; because, while all animals have souls, not all—not even all men—are prudent. Therefore the soul is something else.

§ 42. Lastly, at ‘All those therefore,’ he states that all who have regarded animate beings from the standpoint of movement, i.e. as self-movers, thought that the chief mover in them was the soul, as the above-mentioned opinions show.

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BOOK 1, CHAPTER II, CONTINUED

PREVIOUS THEORIES. EMPEDOCLES, PLATO, SOUL AS SELF-MOVING NUMBER

All who have considered it as knowing and perceiving realities identify the soul with the [elemental] principles,—some making several principles, others one. § 43-4

Empedocles, for instance, says that it is composed of all elements, and that each of these is a soul, saying,

As by earth we know earth, by ether divine ether,

By water water, by fire, it is clear, fire mysterious and hidden;

Love by love, hate by sad hate. §45

In the same way Plato in the Timaeus constitutes the soul from the elements. For like [he says] is known by like; and things are made up of elements. §§46-7

In the lectures ‘On Philosophy’ he likewise lays it down that the animate itself is compounded of the idea of the One, together with the primary Length and Depth and Breadth; other things existing in the same manner. § 48-50

Again, rather differently, that intellect is the One, knowledge the Two (for [this proceeds] as one to one), and the number of the Plane belongs to opinion, and that of the Solid to sensation. For he said that numbers are the specific forms and principles of beings, and are themselves constituted from elements. Some things are discerned by understanding, some by science, some by opinion, some by sensation. But these same numbers are the specific forms of things. § 51

But since the soul seems to be both a moving and a knowing principle, some have made it out to bea combination of these two, stating that it is a self-moving number. § 52

ST. THOMAS’S COMMENTARY

LECTIO FOUR

§ 43. Having shown how some have approached a knowledge of soul through movement, the Philosopher now turns to those who came to it by way of sensation or knowledge. He does this in. two stages. First he shows where the latter were in agreement; and secondly, at ‘Empedocles, for instance,’ where they disagreed.

He begins then by saying that all who studied the soul in or through its knowing and sensing agreed in holding that the soul was composed of the principles of things; but some ‘made’, i. e. posited, many such principles, while others posited only one. Even the earliest philosophers assumed these principles to be in the soul, as though compelled by the force of truth itself; they dreamed, as it were, of the truth. The truth, in fact, is that knowledge is caused by the knower containing a likeness of the thing known; for the latter must be in the knower somehow. The early philosophers, however, thought that it existed in the knower in its own natural being, i.e. with the being that it has in itself. Like, they said, must be known by like. If then the soul is to know all things it must contain a likeness of all things according to their natural mode of being. They could not distinguish between the mode of existence that a thing has in the mind or the eye or the imagination from that which it has in itself. Therefore, since whatever is of a thing’s essence is a constituent principle of the thing, and to know its constituent principles is to know the thing itself, these philosophers maintained that the reason why the soul can know all things is that it is made up of the principles of all things. This theory was common to them all.

§ 44. But they differed about these principles. They did not all admit the same; one admitted many, another only one, and one this and another that. Hence they disagreed also about the constituents of the soul.

§ 45. So, at ‘Empedocles, for instance,’ Aristotle states these differences. He gives first the opinion of Empedocles, saying that the early philosophers who studied the soul by way of its sense-perceptions thought it was composed of the elements. Those who admitted only one principle said that this precisely was the soul; and those who admitted many said that the soul was made up of many; thus Empedocles held that the soul was constituted by all the elements, and that each of these was itself a soul. Note that Empedocles admitted six principles: four material, namely earth, water, fire and air; and two active and passive principles, namely strife and friendship. And since he assumed that the soul knew all things, he said it, was composed of all these principles. Thus as earthy we know earth; as ethereal or airy we know air; as aequous we know water; and as fiery, of course, we know fire. Through love we know love, and through ‘sad hate’ we know hatred. ‘Sad’ comes in here because Empedocles wrote in verse.

§ 46. Next, when he says ‘In the same way Plato’ Aristotle states the opinion of Plato who also, he says, made the soul consist of elements, i.e. be constituted by the, principles of things. And as evidence for this statement he takes three passages from Plato. The first is from the Timaeus, where Plato says that there are two elements or first principles, Identity and Difference. For there is a certain kind of nature that is simple and unchanging, as are immaterial things; and this nature he calls Identity. And there is another kind which does not stay the same, but undergoes change and division, as do material things; and this nature he calls Difference. And it is of these two principles, of Identity and Difference, that the soul, he says, is composed; not that the two are in the soul as its parts; but rather as in the mean between extremes; for the rational soul is by nature lower and less noble than the higher and purely immaterial substances, but it is higher and nobler than inferior material things.

§ 47. Now this opinion rests on the principle already mentioned, that like is known by like. For it seemed to Plato that if the soul knew all things, and if Identity and Difference were fundamental principles, then the soul itself must be constituted of Identity and Difference; in so far as it participated in ‘Identity’ the soul, he thought, knew the ‘identical’, while so far as it participated in ‘Difference’ it knew the ‘different’, i.e. material things. Hence the actual process of the soul in knowing things. For when it gathers things together under genera and species, then, said Plato, it manifests Sameness or Identity, but when it attends to accidents and differentiations he finds in it Difference. That is how Plato in the Timaeus understood the soul as made up of principles.

§ 48. The second passage, showing that this was Plato’s theory, Aristotle refers to when he says ‘In the lectures “On Philosophy”.’ Here too the soul is represented as constituted from principles. Note, in this connection, that Plato took the objects known by the intellect to be things in themselves, existing apart from matter in perpetual actuality, and the causes of knowledge and of being in things of sense. For Aristotle this view involved so many difficulties that he was compelled to excogitate the theory of the ‘agent intellect’. But from Plato’s position it followed that to what could be thought of in the abstract corresponded subsistent and actual realities. We can, however, form abstractions in two ways: one is by proceeding from particulars to universals; and the other is that by which mathematical objects are abstracted from objects of sense. So Plato found himself obliged to posit three types of subsistent being: the objects of sense-perception; mathematical objects; and universal ideas-these last being the cause, by participation, of the other two types.

§ 49. Plato also held that numbers were causes of real things, being unaware of the distinction between unity as identical with being, and unity as the principle of the number that is a kind of quantity. Hence he inferred that universals were of the nature of number; for the universal existing separately is the cause of things whose substance is numerical. He said indeed that the constituent principles of all beings were ‘species’ and ‘specific number’, which he called specific in the sense of being constituted from ‘species’. And he reduced number itself to unity and duality as to its fundamental elements; for, as nothing can proceed from one alone, there must, he thought, be some nature, subordinate to unity, whence multiplicity might proceed; and this nature he called duality.

§ 50. Thus Plato envisaged three classes of beings, graded according to their connection with matter. As sensible objects are more material than the objects considered in mathematics, and the latter more so than the universal ideas, he placed sense-objects on the lowest level, and above them mathematical objects, and above these the separately existing universals and ideas. Universals differ from mathematical objects in this that the latter include numerical differences Within the same species, whereas ideas and separated substances exhibit no numerical differences in the one species; there is but ore idea for each species. These ideas, he said, are numerical in nature, and from them are derived such numerical qualities of sensible things as length, breadth and depth. Hence he said that the idea of length was the primary duality, for length is from unit to unit, from point to point; and that of breadth was the first trinity, for the triangle is the first of plane figures; and that of depth, which includes both length and breadth, was the first quaternity, for the first solid figure is the pyramid which is constructed of four angles. So too the sensitive soul, in Plato’s system, implied a Soul existing separately as its cause, and constituted, like the other ‘separate’ things and ideas, by number, that is, by the unity and duality which for him were fundamental in ,things.

§ 5 1. Then at ‘Again, rather differently,’ Aristotle alludes to the third text adduced to show that for Plato the soul was made up of elements or principles. As we have said, it was Plato’s view that the specific forms and, principles of things were numbers; so when he came to treat of the soul he based its knowledge of things on its fundamentally numerical composition; all of its activities, he maintained, sprang from this source. Take for instance the diverse apprehensive functionings of the soul: simple understanding, science, opinion and sensation. Simple understanding Plato connected with the idea of One; it has the nature of Unity; for in one act it apprehends a unity. Again, science for him relates to Duality since it proceeds from one to one, i.e. from principles to conclusions. And opinion relates to the first Trinity, proceeding from one to two, i.e. from principles to a conclusion which is accompanied by the fear that a different conclusion may be true; so forming a triad out of one principle and one admitted and one feared conclusion. Finally, sensation derives from the first Quaternity, i.e. from the notion of a solid body constructed (as we have said) from four angles; for bodies are the object of sensation. Since then all knowing is contained in these four, i.e. in simple understanding, science, opinion and sensation, all of which, said Plato, are in the soul in virtue of its participating in the nature of Unity, Duality, Trinity and Quaternity, it obviously follows that for Plato the separated Soul, the ‘idea’, as he called it, of particular souls, was constituted by numbers, which are the elements or principles of reality. So much to show that Plato regarded the soul as made up of principles.

§ 52. Next at ‘But since the soul seems,’ Aristotle observes that some philosophers defined the soul, and came to know something about it, through both movement and sensation or knowledge. He says that, as the soul seemed to them to be both self-moving and cognitive, they joined the two aspects in their definition and called it a ‘self-moving number’. ‘Number’ refers to the cognitive power because they thought, in accordance with what has been said already, that the soul was able to know in virtue of its participating in the nature of specific number (Plato’s opinion). ‘Self-moving’ refers to the soul’s motive power.

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BOOK I, CHAPTER, II, CONTINUED

PREVIOUS THEORIES

SOUL AS IDENTIFIED WITH THE ELEMENTS

Opinions differ however as to the elemental principles—what they are, how many they are; and the difference is greatest between those who make these corporeal and those who make them incorporeal. But some, making a mixture, have defined the principles in terms of both. They differ also as to the number, some positing one, others several. And they assign a soul to these [principles] accordingly. (For they not unreasonably assumed that what by nature causes movement was primary.) §§ 53-4

Hence some have held it to be fire; for this is the most subtle, and much the least corporeal of the elements; moreover, it moves itself, being the first cause of movement in other things. Democritus said something which rather neatly gives the reason for either fact. He said that soul is the same as mind, and that this originates in primary indivisible particles and that it causes motion by its fineness and shape. He says that the sphere is the most light and mobile of shapes, and that fire and mind must both be of such a nature. §§ 55-6

Anaxagoras, however (as we said above), seems to speak of soul and mind as diverse, yet he employs both terms as for a single essence. Nevertheless, he posits Intellect as the principle par excellence of the Universe, saying that this alone among beings is simple, unmixed and pure. He attributes, indeed, to the same principle both knowing and moving; saying that the Intellect moves all things. § 57

It seems that Thales, from what they recollect of him, was also of opinion that the soul was a cause of motion,—if it is a fact that he said that the magnet had a ‘soul’ because it attracts iron. §58

Now Diogenes, like certain others, held that air is the most subtle of all things and is their principle; and is the cause of the soul’s knowing and moving. As primary, it is cognitive of all else: and as the most subtle thing, it is the motive force. § 59

Heraclitus, however, says that soul, as a principle, is some vapour of which it is constituted, since this is the least corporeal of substances and is always flowing; and that any moving object is known by a moving object—he and many others holding that all realities are in movement. § 60

Alcmaeon seems to have held opinions on the soul similaR to these. For he said it was immortal because it. bore a resemblance to immortal beings. And this he attributed to it because it always moves; all heavenly things seem to be in motion continually—the sun, the moon, the stars, all heaven. § 61

Some cruder thinkers, like Hippo, thought it was water. They seem to have been persuaded of this because semen is liquid in all animals. For he confutes those who say the soul is the blood, on the ground that semen, which is the inchoate Soul, is not blood. § 62

Others, such as Critias, held it was blood; that sensation was most distinctive of the soul; and that it was due to the nature of blood that this power was in it.

For opinions have been given in favour of every element excepting earth: which no one has proposed, unless whosoever may have said it was derived from all the elements, or was identical with them, did so. § 64

All, taken together, define soul, we may say, by three things: by movement, by sensation, and by immateriality. And each of these is reduced to elemental principles. Hence, in defining it as cognitive, they make it either an element or consist of several elements, one saying much the same as another (with a single exception). For they say that anything is known by what resembles it, and as the soul knows all things, go they constitute it of all principles: some saying that there is one cause and one element, and that the soul is a single thing—fire or water, for example; others that there are several principles, and that the soul is multiple. § 65

But Anaxagoras, standing alone, says that mind is beyond the reach of influence and has nothing in common with other things. But, granted that this be true, he, did not explain how it acquires knowledge, in virtue of what cause; nor is this made clear by anything else he said. § 66

Those who posit contraries as first principles also maintain that the soul consists of such contraries, while those who favour some one among contraries (hot or cold, or some other like these) make the soul, accordingly, one of these. Whence also some follow names, as those who allege that it is heat, because life is due to heat and is named from it. But those who identify the soul with cold say that it is named from respiration and breathing.

Such then are the opinions that have been transmitted to us about the soul, together with the reasons given for them. § 67

ST. THOMAS’S COMMENTARY

LECTIO FIVE

§ 53. In the preceding chapters Aristotle has shown the old philosophers agreeing in their analysis of the soul, in that they all regarded it as the origin of movement and knowledge. in the section beginning now he shows how they variously interpreted that common presupposition. This section falls into three parts: in the first he shows the root of the divergence of these philosophers in their teaching on the soul; the second enumerates the various points of difference (beginning at ‘Hence some’); the third summarises all that we have to consider in these differences (at ‘All, taken together’). The root of the divergence of the philosophers in their teaching on the soul is to be looked for in the way they analysed it into its ultimate elements; as they disagreed about these elements so did they differ about the soul. They all agreed that the soul was made up of ultimate elements, but they could not agree that it was made up of the same elements; and, differing as to the elements, they differed in their theories of the soul.

§ 54. They differ in two ways about the ultimate elements: first, as to their essential nature, i.e. ‘what’ they are; secondly, as to their number, ‘how many’ they are. As regards their essential nature, some said these principles were corporeal (fire or water or air) while others said they were incorporeal and immaterial, such as those who spoke of numbers and ideas; and there were others, like the Platonists, who blended both views and allowed that there existed both sensibly perceptible and separate immaterial principles. As to their number or multiplication, there were some who admitted only one principle. Heraclitus, for instance, said it was air; and someone else, fire; while others said there were many principles—Empedocles for instance, who maintained the theory of the four elements. And their theories of the soul in respect of the elements followed these various hypotheses concerning ultimate elements. Those who held to a theory of material first principles, like Empedodes, said the soul was composed of such; and those, like Plato, who held to immaterial principles, said that the soul was composed of these. But one and all considered the soul to be the chief source of movement.

§ 55. Next, at ‘Hence some’, he proceeds to run through the more particular differences between the philosophers. it should be noted that of those who thought that a corporeal thing was the first principle, not one deigned to identify this with mere earth. Some said it was fire, others air, others water, but nobody said it was earth, except those who thought that all the four elements together were the first principle. (The reason being that, with its density, earth seemed always to presuppose some more ultimate principle). Aristotle, then, does three things here. He gives first the views of those who identified the first principle and the soul itself with fire; secondly, of those who held that they were air (at ‘Now Diogenes’); and thirdly, the opinion of those who held that water was both the first principle and the soul (beginning at: ‘Some cruder thinkers’).4

§ 56. As to the first of these groups, we should note that since movement and knowledge were ascribed to the soul, it appeared to some that the soul possessed these properties in the highest degree; and as movement and knowledge seemed to connote what is lightest and most rarified, they concluded that the soul was fire, which is the lightest and most rarified of bodies. And. while many were of this opinion and thought the soul was fire, Democritus more subtly and rationally explained ‘the reason for either fact’, that is, he expressed more clearly the nature of movement and of knowledge. He held, as we have seen,, that all things are made of atoms; and though for him these atoms were primary he maintained, nevertheless, that the round ones were of the nature of fire, so that the soul, he said, was composed of spherical atoms. Considered as first principles, these atoms were by nature cognitive, but considered as spherical they were mobile; hence he said that the soul knows and moves all things precisely because it is made up of these round, indivisible bodies. And in assuming that they were of the nature of fire, he agreed with those who thought that everything was fiery.

§ 57. Then at ‘Anaxagoras, however’, Aristotle gives the view of Anaxagoras who agreed with the others already mentioned in ascribing knowledge and motion to the soul. Anaxagoras, as we saw, sometimes appears to distinguish between soul and intellect, but sometimes he uses both terms as though they meant the same thing. He ascribes to the soul motive power and knowledge, but he also says that intellect knows and moves all things, thus identifying the soul and the intellect. But he differed from the others in this, that whereas Democritus held that the soul was corporeal by nature, being composed of material elements, Anaxagoras said that intellect was ‘simple’, excluding intrinsic division from its essence, and ‘unmixed’, excluding composition with anything else, and ‘pure’, excluding any addition to it from outside. But he ascribed movement and knowledge to one and the same principle, i.e. the intellect; for intellect of its nature knows; and movement pertains to it, so he said, because it moves everything else.

§ 58. Next, at ‘It seems that Thales’, he states the opinion of a philosopher called Thales who had only this in common with the others mentioned above, that he identified soul with a motive force. This Thales was one of the Seven Wise Men; but while the others studied moral questions, Thales devoted himself to the world of nature and was the first natural philosopher. Hence Aristotle remarks ‘from what they recollect etc.’, referring to those who said that water was the basic principle of things. For Thales thought that the way to find the principle of all things was by searching into the principle of living things, and since all the principles or seeds of living things are moist, he thought that the absolutely first principle must be the most moist of things; and this being water, he said water was that principle. Yet he did not follow his theory to the point of saying that soul was water; rather, he defined it as that which has motive force. Hence he asserted that a certain stone, the magnet, had a soul because it moved iron. Anaxagoras and Thales, then, are included in the present list; not for identifying the soul with fire, but because the former said that the soul was the source of knowledge and sensation, and the latter that it was at the ,origin of movement.

§ 59. Where he says, ‘Now Diogenes’, Aristotle alludes to those who thought that air was the first principle and the soul. There were three of these. First there was Diogenes who held that air was the first principle and also the finest-grained of all bodies, and that the soul therefore was air,—hence its power to know and move. The knowing power was due to the fact that air was (as he said) the first principle; for as knowledge is through likeness, as we have seen, the soul could not know all things unless it included the principles of all. And the moving power was due, he said, to the fact that air was the finest-grained of bodies and therefore the most mobile.

§ 60. Then at ‘Heraclitus, however’ he states the second opinion, that of Heraclitus who thought that not mere air but vapour, the blend of air and water, was the first principle. He could not allow that this was either water by itself, or fire, or air; it had to be something betwixt and between, because, being a materialist, he was concerned to find a principle midway between the opposite extremes of material quality. Thinking that vapour answered this requirement most precisely, he said that the soul was vapour; which explained its extraordinary capacity to know and to move. His view was, indeed, that everything was in continual flux, that nothing stayed the same even for one hour, and that no definite statement could be made about anything. And it was just because vapour is so unstable that he identified it with the first principle of all things; which, he said, was a soul. As the first principle, soul has the power to know, whilst as the least material and most fluid of things it has movement.

61. Thirdly, at ‘Alcmaeon seems,’ he gives the third opinion, Alcmaeon’s, which agrees with the others only as regards movement. This man said that the soul was pre-eminently a thing in motion, resembling in this the immortal heavenly bodies with their heavenly and divine nature. For he thought that the perpetual movement of the sun and moon and the rest, was the cause of their being immortal; and that the same inference was valid in the case of the soul.

§ 62. Then at ‘Some cruder thinkers’, Aristotle states an opinion of some who made water the first principle. For there were certain rather crude followers of Thales who tried to make the principle of one particular thing an analogy of the first principle of Nature as a whole. Observing that moisture was fundamental to living things they concluded that it must be the first principle of an things; in short, that the latter was water. So far indeed they followed their master, Thales; but whereas he, though admitting water to be the first principle, would not, as we have seen, allow that the soul was water, but rather a motive force, his cruder disciples (such as Hippo) asserted that it was water. Hippo tried to refute those who said the soul was blood with the argument that blood is not the generating seed (which they called ‘the inchoate soul’) of animate things. He identified this with water on account of its humidity.

§ 63. Next, at ‘Others, such as Critias’ he alludes to a philosopher who was more interested in the soul’s knowledge. He was still cruder in his expressions, saying that the soul itself was blood. His reason was that sense-perception only takes place in animals through the medium of blood: for the bloodless organs, such as bones, nails and teeth are without sensation (he forgot the nerves which are extremely sensitive and yet bloodless). If then, he said, the soul is the root of knowledge, the soul must be blood. it was Critias who said this.

§ 64. In case anyone should wonder why he has not mentioned earth along with the other elements, Aristotle, at, ‘Opinions have etc.,’ explains that his predecessors’ views on the soul followed on what they thought about the first principles; and as nobody judged earth to be a first principle, nobody said it was the soul; unless we count those—such as Democritus and Empedocles—who said that soul was, or was composed of, all the principles.

§ 65. Then, at ‘All, taken together,’ he summarises, concluding this part of the enquiry; and first with reference to the elements or principles themselves, and then with regard to the contrarieties that are found in them.

First, then, he notes that the soul has been described by all-in terms of these three notes: fineness of grain or texture (incorporeality); knowledge; movement; and that each of these notes has been also traced back to a first principle. For that is called a principle which is simple. Also a principle, it is said, is essentially cognitive (for, to recall what, was said above, I since like is known by like, they said that the soul was composed of, or even was, the elements of all things. Anaxagoras, to be sure, is an exception with his pure unmixed Intellect). Again, they identified the chief motive-force in things with a ‘principle’ since a principle is what is least corporeal. And the soul’s knowledge of all things proves, they said, that it was composed of all the principles or elements. All their theories turn on this correspondence between the soul and the first principles. Whoever posited some one cause or principle or element, such as fire, air or water, identified just that one with the soul. So, too, whoever upheld many principles either identified them with the soul. or with its component elements.

§ 66. Having excepted Anaxagoras, touching the theory of the soul’s composition, he goes on, at ‘But Anaxagoras’ to show how this man differed from the others. He alone, says Aristotle, denied the passivity of the intellect, its share in the nature of the things that it knows. But how intellect knows, Anaxagoras does not say; nor can one infer anything certain from what he does say.

§ 67. To end this section, Aristotle summarises what he has to say touching the contrariety of the above-mentioned principles to one another. Some, he says, arrange the first principles of things in pairs of opposites; and the soul also they regard as a synthesis of contraries. Thus Empedocles thought that the heat and cold, the moisture and dryness which he found ‘in the elements were intrinsic to the soul also. As earthy, he said, we know earth, as watery water, and so on. Others found their first principle in only one element, whose particular quality they then attributed to the soul. If it was fire, then the soul, they said, was hot; if water, then the soul was cold. According to the principle assumed so was the quality attributed to the soul, as though it shared in the nature of heat or cold etc. This is clear from the names they gave to the soul. Those who said it was hot gave it names derived from zaein or zooein, meaning to live, which itself comes from zeein, meaning to boil; while others who said it was cold called it psychron, meaning cold, whence comes psyche, a term applied to the soul because the coolness caused by breathing preserves animal life. Those who thought the soul by nature hot, named it from life; those who thought it by nature cold, from respiration. And Aristotle concludes by saying that the foregoing are the opinions handed down about the soul, together with the grounds on which they are maintained.

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BOOK I, CHAPTER III

PREVIOUS THEORIES

SOUL AS A SELF-MOVING ESSENCE

The first thing to be considered is movement. For perhaps it is not only false to say that this is the essence of the soul, as some mean when they say the soul is self-moving, or is able to move itself, but that there should be movement in it at all is an impossibility. It has already been stated that it is not necessary that everything that causes motion be itself moving. For everything moves in one of two ways: either by another, or of itself. We say, ‘by another’, of anything that moves through being in that which moves, like sailors; for these are not in motion in the same way as the ship. The latter moves of itself, but they through being in what moves. This is evident if we consider their parts. Walking is the proper motion of the feet—and also of men—; but for the time being the sailors do not walk. Movement being thus predicated in two ways, we now turn to the soul, asking whether it moves of itself and participates in motion. §§ 68-74

Since there are four kinds of movement (local, by alteration, by increase, by decrease) its motion must be one of these, or some, or all. But if its movement is not incidental, then motion will be in it by nature: and if so, it will be [in] place; for all the aforesaid movements are in place. If it is the essence of the soul to move itself, to be in motion will not be in it incidentally, as in what is white or three cubits long; for these also participate in movement, but incidentally. For what moves is the body in which these inhere; hence of themselves they have no place; but the soul has it, if indeed it naturally participates in motion. §§ 75-7

Further, if it moves by nature, so it will move by force; and if by force, then, by nature. And its rest will be in the same way. Whithersoever it moves by nature, there it will come to rest by nature; and likewise wheresoever it is moved by force, there it will come to rest by force. But what kind of enforced motions and rests will there be in the soul? To find an answer is not easy, nor, even to imagine one! §§ 78-9

Again, if it moves upwards, it will be fire; and if downwards, earth; for such are the movements of these bodies; and the same holds of the intermediate [elements]. § 80

Since it seems to move the body, it would seem reasonable [to say] that it does so by the same motions as those by which it moves itself. If so, then it is true to say, conversely, that just as the body moves, the soul also moves. Now the body moves by change of place; hence the soul too will move in accordance with the body, either the whole or the parts being transposed. If this is so, then it might happen that after leaving the body it could return to it. (But it is utterly impossible that the dead rise again.) And it would follow that dead animals could rise again. §§ 81-83

If it does move, however, by something else, its motion will be incidental; for certainly an animal can be driven by force. But what has self-movement as of its essence cannot be moved by another, save incidentally; as that which is good in itself or for its own sake cannot exist for the sake of another, or on account of another.

One might certainly say that, if the soul is moved at all, it is moved by the objects of sensation. §§ 84-5

But if it moves itself it also is in motion. Hence if all motion is a displacement of the moved as such, then the soul must be displaced from its own essence by itself, unless its movement be incidental; but [in fact] this is a self-movement of its essence. § 86

ST. THOMAS’S COMMENTARY

LECTIO SIX

§ 68. The Philosopher now begins to criticise the theories he has been recounting. These theories amount to three statements about the soul: that it is the source of movement and of knowledge, and that it is in a special way incorporeal. The two former attributions, the principal ones, have been predicated of the soul in an absolute sense, as referring directly to its essence. The third is, however, true in one sense and false in another. For if immateriality is taken as predicated simply and absolutely of the soul, then the statement is true; for soul is certainly the least material and most rarified of things. But if it is predicated only in relation to the body, as if to say that soul is the least material of bodies, then the statement is not true. Hence the Philosopher sets to work only with the two former attributions, of movement and of knowledge.

§ 69. This part of the treatise falls into three divisions. Aristotle first argues against the philosophers who had made the soul the source of movement; then at ‘There are then three ways’ against those who regarded it as the seat of knowledge; and thirdly, at ‘Since knowledge pertains’ he raises the question whether movement, feeling and knowing ought to be attributed to the soul as to one principle or several. The first of these divisions is again divided. He first adduces objections against simply identifying the soul itself with a source of movement; and then against an opinion, proceeding from this identification, according to which the soul was also a self-moving number. (This comes at ‘Much the most unreasonable’. ) The former argument again subdivides into, first a criticism of the way in which these philosophers had predicated movement of the soul, and secondly, at ‘One might with more reason,’ a query whether this predication might have been made differently. Then the criticism is divided into, first, a general argument against all who said that the soul was the source of movement; and secondly, at ‘Some say that a soul moves’ a series of particular discussions of special points. Finally, the general argument is subdivided. First, he says what he intends to do; secondly, he argues ‘in support of his own opinion. The latter begins at ‘Since there are four kinds of movement’.

§ 70. He begins then by remarking that philosophers have studied the soul from two points of view, from motion and from knowledge. This is clear from what has been said. And Aristotle says that he will start from motion. Now all the others who started from this point of view had one notion in common, that everything that produces movement is itself moving. They thought therefore that if soul is by nature a cause of movement, it must be by its nature a moving essence. So they put movement into its definition, calling it something that moves itself.

§ 71. Now here there are two disputable points; the theory itself is disputable, and so is the principle upon which it rests. The principle presupposed as a self-evident truth, namely that every active mover is itself in movement, is in fact not true, as is clearly enough shown in Book VIII of the Physics, where Aristotle proves the existence of an unmoved mover. And as to this, we may give here a short proof that if a thing produces movement it does not have to be in movement itself. It is clear that in so far as a thing produces movement it is in act, and in so far as it is caused to move, it is in potency. (if then as causing movement it were moved), the same thing would be in act and potency in the same respect; which hardly makes sense.

§ 72. But even setting this difficulty aside, the theory that the soul is in movement is disputable. Its upholders indeed added the further proposition, that movement was of the soul’s essence; but Aristotle denies both parts of this theory where he says, ‘For perhaps’, etc. He puts it like this because he has not yet proved his assertion, namely that not only is it false to say that movement is of the essence of the soul (which is what they imply when they define the soul as an actual or potential self-mover) but that it is also quite impossible that the soul should move at all.

§ 73. That not everything which causes movement need itself be moved was shown in an earlier work, Book VIII of the Physics. Now in any self-mover there are two things to be considered, the thing moving, and the thing moved; and the former cannot as such be the same as the latter. In living things, however, though the moving part is not moved in itself, absolutely speaking, yet it is moved indirectly. For there are two kinds of movement, direct and indirect: direct, when a thing itself is moving, e.g. a ship; indirect when a thing itself is at rest, but moved with the movement of something else which contains it, as the sailor on board ship moves with the ship’s movement, not his own. So the ship moves directly and in itself, but the sailor only in an accidental way or relatively. This is clear if we consider that when anything moves in itself, its parts are moving, as in walking the feet make the first movement; but once the sailor is on board this does not happen. Movement then can be taken in either of these two senses; but since the philosophers we are discussing said that the soul is moved in itself, directly, we can forgo at present the question whether it is moved indirectly, and consider only whether it is directly affected by movement, as they maintained.

§ 74. To show that the soul does not move in itself, Aristotle uses six arguments, with regard to which we should note that, while they may not appear very cogent, still they are effective in relation to the theory he is criticising. For it is one thing to argue out the simple truth of a question, and another to reason against a particular theory; in the former case you have to make sure that your premisses are true, but in the latter you proceed from what your adversary concedes or asserts. Hence it is that when Aristotle criticises the views of others, he often seems to use rather weak arguments. In each case he is, in fact, destroying his adversary’s position by drawing out its logical consequences.

§ 75. The first argument begins at ‘Since there are four kinds’, and may be stated as follows. If the soul moves, its movement is either direct (in the sense explained) or indirect. if indirect, then it is not of the essence of the soul (which is against their opinion), and the soul moves in the same way as whiteness or 3 inches, which are accidental qualities moving only with the thing that is white or 3 inches long, and not themselves, as such, requiring a position in space. But if the soul moves in itself, it moves in one of the four kinds of movement: change of place, growth, decrease or alteration. Coming-to-be and passing-away are not movements, strictly speaking, but changes, because they are instantaneous, whilst movements are successive. Hence the soul will have to move in one of these four ways—from place to place; by increase or decrease in size; or by qualitative alteration. But if all these movements involve position in space, the soul will then be localised in space.

§ 76. There seem to be two doubtful points in this argument. The first is that, while it is clear enough as regards locomotion, growth and decrease, it suggests a difficulty about alteration. Some meet this difficulty by saying that as only bodies are subject to alteration, and all bodies are in place, alteration itself may be said to occur in place. But this does not keep to the letter of the argument: Aristotle says that this kind of movement is in place and not merely according to place. Movement in place is quite different from movement according to place; and, following Aristotle, I maintain that alteration certainly occurs in place. Of itself, and not simply because of its localised subject, it is in place; for, when any alteration occurs, the agent producing it must draw near to the thing altered; otherwise nothing would ever be altered. And since drawing near is a local movement, it follows that here and now the cause of a given alteration is a change in place.

§ 77. The second difficulty is that these philosophers do not in fact see anything unreasonable in the soul’s being in place, since they maintain that it moves in itself, absolutely. So Aristotle’s objection seems to misfire. To this two answers might be given, (a) that the objection to the soul’s being in place will become clearer as we proceed, and (b) that if the soul were in place, it would have to be assigned a definite position in the body and thus would not be the form of the whole body. This reinforces the objection to the soul’s being in place.

§ 78. The second argument, at ‘Further, if it moves’, is this. If the soul moves ‘absolutely’ from place to place, the movement must be natural to it. But anything that can be moved naturally can be moved violently.’ Now its natural movement implies a natural ceasing to move; and therefore also its enforced, violent movement implies an enforced ceasing to move. Hence the soul may both move and stop moving under compulsion; which is impossible if by nature both its movement and ceasing to move are spontaneous.

§ 79. A difficulty here seems to be that what moves naturally does not in fact move under compulsion. I answer that what Aristotle says is false absolutely speaking, but true relative to the theory under discussion. For these philosophers maintained that the only bodies that moved with a natural movement were the four elements; in which we do observe both natural and enforced movement and ceasing to move. This opinion is presupposed by the argument.

§ 80. The third argument, at ‘Again, if,’ runs as follows: these men who ascribe movement primarily to the soul, and to the body only as derived from the soul, also say that this movement is due to one or other of the elements, fire or earth or one of the others. But if the soul moved with the nature of fire it would only rise; if with the nature of earth it would only sink; whereas in fact it moves in all directions. This argument also is ad hominem.

§ 81. The fourth argument comes at ‘Since it seems’. It is this. You say that it is in moving the body that the soul moves. Logically, then, it follows that it moves the body by its own movements; and conversely that it is moved by the same movements which move the body. But the body moves by changing position in space; so also then the soul. But if the soul’s local movements affect the body, the soul might, after leaving the body, enter it once more. And since it is the soul’s presence that gives life to the body, it follows that dead animals might, even naturally, come back to life: which is impossible.

§ 82. Against this argument some have objected that it ignores the difference between the movements which affect the soul itself and those by which it moves other things, including the body. The former are movements of desire and will; not so the latter. But in reply one may say that desires and volitions and so on are not properly ‘movements’ of the. soul but ‘operations’. ‘Movements’ and ‘operations’ are different: a movement is an act of something that is incomplete, whereas an operation is an act of a subject already possessing full actuality. Still, what Aristotle says is true relative to the theory under discussion; for this had identified all the movements of the soul with those by which it moved the body.

§ 83. But is it true that if the soul had local movement dead animals would come to life again? Well, some philosophers have maintained that the soul pervades the whole body, forming a unity with it through some kind of proportion, and that the two cannot be separated without this proportion being destroyed; so that, so far as this view is concerned, the conclusion would not follow. But it does follow from—and is a valid objection against—the opinion of those who say the soul is located in the body as in a vessel which it sometimes enters and sometimes leaves.

§ 84. The fifth argument comes at ‘If it does move’, and runs as follows. It is clear that when anything is of the essence of a given subject its presence in the latter does not need, except incidentally, to be explained by anything else. If then the soul is essentially moving, it is mobile of its own nature; it does not need to be moved through or by anything else. But we know that it is in fact moved by sensible objects when it senses, and by things desirable when it desires; therefore it does not move of itself.

§ 85. The Platonists meet this argument by denying that the soul is moved by sensible objects; these, they say, are merely involved in the soul’s own movement when it passes from one object to another. But this is untrue. As Aristotle has proved, the intellectual potency is brought into act precisely by means of the sensible objects as apprehended; so that it is moved by them in this way.

§ 86. The sixth argument begins at ‘But if it moves itself’. Clearly, if the soul is self-moving, its own essence governs its movement. But in every movement the moving thing comes away or proceeds from that which moves it and governs its movement; for instance, if anything is moved by a quantity, it departs and proceeds from the latter. If then the soul is moved by its own essence (as they say) it must depart or proceed from its own essence; which is as much as to say that it causes its own destruction. How then could it be through movement that the soul becomes god-like and immortal, as some philosophers whom we have mentioned supposed?, This argument bears against those who did not distinguish between movement proper and operation. For movement implies that what is moved comes away from the cause of movement; but operation is a perfection intrinsic to the operating agent itself

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BOOK I, CHAPTER III, CONTINUED

SOUL AS A MOVER OF THE BODY

DEMOCRITUS AND PLATO

Some say that a soul moves the body in which it dwells just as it moves itself; as did Democritus, who spoke like Philip the comic poet; for the latter relates that Daedalus made a wooden Venus mobile by pouring quicksilver into it. Democritus, then, spoke in like manner, saying that there are in movement indivisible globules of which the nature is to be never at rest, and which therefore draw together and move the whole body. §§ 87-8

Now, what we would ask is, whether this is also the cause of coming to rest? How it could be, on this hypothesis, is difficult to see, indeed impossible. § 89

The soul seems, in general, not to move the animate being in this way, but rather by a sort of choice and understanding. § 90

In the same way, the Timaeus sets out a physical theory as to how the soul moves the body. For, from the fact that the soul moves itself, it moves the body, as a result of its connection with the body. § 91

‘Being compounded of the elements and divided according to harmonic numbers, so that it have a connatural sense of harmony, and the whole be borne along with well attuned motions, §§ 92-8

[God] bent the straight line into a circle, and, dividing it, made out of one two circles, adjusted at two points; and, again, he divided one of these into seven circles, as though the heavenly motions were the soul’s motions.” §§ 99-106

ST. THOMAS’S COMMENTARY

LECTIO SEVEN

§ 87. Having argued in a general way against the view that movement pertains essentially to the soul, the Philosopher now brings forward arguments against particular philosophers whose theories of the movement of the soul seem to give rise to some special difficulty. These arguments fall into three groups. First, he opposes an opinion of Democritus; then, at ‘In the same way’, one of Plato; and thirdly, at ‘There is another opinion’ another theory.

He begins, then, by stating the view of Democritus on the soul’s movement; and then brings objections against it.

§ 88. This theory has already been referred to by Aristotle in his fourth objection to the view that the soul moves in itself and by this movement makes the body move. If the soul moves the body, he has said, it must do so in virtue of its own movement. This was admitted by those who said that each soul moved its own body in a manner corresponding to the movement in itself; among whom was Democritus who made use of the following illustration. There was a certain comic dramatist called Philip who tells somewhere of one Daedalus, that he made a wooden statue of the goddess Venus, and that this statue, being filled with quicksilver, was able to move. It moved as the quicksilver moved. And what Democritus said of the soul’s movement was rather similar. The soul, he said, (as has been noted above) was composed of indivisible spheres or atoms which, being round in shape, were always moving about, and by their incessant movement made the whole body cohere and move accordingly.

§ 89. Then, at ‘Now, what we, etc.’, Aristotle puts two objections to this. First, it is agreed that in animals the soul is the cause of resting, as well as the cause of movement. But according to Democritus the soul is never the cause of rest, though it is the cause of animal movements. For he could hardly maintain that those spherical atoms ever rested if they never cease to move.

§ 90. Again, at ‘The soul seems’ he puts a second objection. The movement caused by quicksilver in the statue is obviously not spontaneous; it is a compelled movement. On the contrary, that of the soul is spontaneous, proceeding from mind and will. Hence the view of Democritus seems worthless.

§ 91. Then at ‘In the same way’ he first states the opinion of Plato, which, at ‘Now in the first place,’ he will reject. But before explaining what Plato said about the soul he shows its similarity to the theory of Democritus. As Democritus had supposed that the soul’s movements moved the body to which it was joined, so also did Timaeus, a speaker introduced by Plato. For he said that soul moves body in so far as soul itself moves; because the two are, as it were, bound up together.

§ 92. With ‘Being compounded, etc.’ Aristotle makes Plato’s view explicit; first as to what constitutes the essence of the soul, at ‘God bent, etc.,’ as to how movement proceeds from it. Regarding the former question, note that the words quoted here are used by Plato in the Timaeus and refer to the Soul of the world which, according to him, is imitated by inferior souls. So when he touches, as here, on the nature of the World-Soul, he refers also, in a way, to any soul. Now Plato, for the reason already given, maintained that the essence of all things was numerical; and that in number the formal element, so to say, was one and the material element two—all numbers being made up of one and two. And as odd numbers retain something of the indivision of one, he laid down two elements of number, the even and the odd, attributing to the odd identity and finitude, but to the even difference and infinity.

§ 93. Some explanation of this theory may be found in the Physics, Book III. If odd numbers are added to unity in sequence the same type of number 2 always results; e.g. if 3, the first odd number, is added to 1, you get the square number 4; if to 4 You add the second odd number, 5, you get 9, Which is also a square number; and so on to infinity. But with even numbers the result is always a different type of number. Add 2, the first even number, to 1, the result is the ‘triangular’ number 3; to which if you add 4 the second even number, you get 7 which is ‘septangular’; and so on to infinity. Hence Plato made Identity and Difference the first elements of all things, attributing the former to odd numbers, the latter to even.

§ 94. And because he placed the soul mid-way between the higher substances, which never change, and corporeal substances, which change and move, he thought that the soul was constituted of the elements of Identity and Difference, and so of odd and even numbers. For the mean must participate in both extremes. This is why Aristotle says that Plato held the soul to be constituted by these elements.

§ 95. Again, we should note that in numbers there are different proportions and infinities, of which some are harmonic, i.e. the cause of harmony. The double proportion causes the harmony called a whole octave; that of 3 to 2 causes the harmony called a fifth; (that of 4 to 3 causes the harmony called a fourth); that of 9 to 8 causes a tone; and the other harmonies are caused by other proportions: for example the harmony composed of an octave and a fifth is caused by the triple proportion; that of the double octaves is caused by the quadruple proportion which was discovered by Pythagoras, as Boethius [De Musica, I, 10] relates, from the striking of four hammers which sounded in harmony according to the aforesaid proportions. Thus if one hammer weighed twelve ounces, one nine, one eight and one six, the one that weighed twelve ounces would be in the proportion of two to one to the one weighing six, and the two together would render the harmony of the octave. Again, the one weighing twelve ounces would be as three to two to the one that weighed eight, and the harmony produced would be that of a fifth; similarly in the case of those that weighed nine ounces and six ounces. Again, the one weighing twelve ounces is in the proportion of from four to three to the one weighing nine, and in es with it the harmony of a fourth; so also does the one that weighs eight with that weighing six; while the one weighing, nine is proportioned to the one that weighs eight, and produces with it the harmony called a tone.

§ 96. But if Plato reduced everything to numbers, these were not harmonic numbers, except in the case of the soul. Hence Aristotle gives it as Plato’s view that the soul was ‘divided’. or, as it were, weighed out, ‘according to harmonic numbers’, i.e. to numbers related to each other in musical proportions. He said that the soul was constituted of the numbers 1, 2, 3, 4, 8, 9 and 27; in which these harmonic proportions are found.

§ 97. And he had two reasons for thinking this. One was the fact that similarity and connaturality are always a cause of pleasure. We find the soul taking pleasure in all harmonies and disliking whatever is unharmonious in sounds and colours and indeed in any sensible quality. So harmony seems to be natural to the soul. This is what he means by saying that the soul has ‘a connatural sense (i.e. knowledge) of harmony’.

§ 98. The second reason is that the Pythagoreans and Platonists thought that beautifully harmonious sounds resulted from the movements of the heavenly bodies; and since they supposed these movements to be caused by the World-Soul they naturally concluded that the soul was made up of harmonic numbers. Hence Aristotle says ‘that the whole (i.e. Universe) be borne along with well-attuned motions’.

§ 99. Next, when he says ‘God bent, etc.” Aristotle explains how the World-Soul is the cause of heavenly movements. Taking all numbers ‘in their natural order, we must think of them as laid in a straight line, each one adding to the preceding one. Now the natural numerical series can give rise to several other series; for example, one might take the geometrical series whose common ratios are 2 or 3 or 4, and so on for other ratios. As then man, by thought, can manipulate numbers, so does God in building up the substances of things from numbers. In constructing the soul’s substance out of the aforesaid numbers, namely all those placed in a straight line series according to their natural order, he divides them into two series: one, the geometrical series whose common ratio is 2; the other, the geometrical series whose common ratio is 3; because these two embrace all the harmonic proportions. For the double proportion is divided into the ratios 3:2 and 4:3; the triple into 2:1 and 3:2. Therefore the above-mentioned numbers are taken, in the geometrical series with common ratio 2, up to the first cube number, e.g. 1,2,4 up to 8; so also with the series with common ratio 3, e.g., 1,3,9,27. These two series meet at unity like two straight lines containing an angle.

§ 100. Moreover, if the numbers in the series whose common ratio is three are joined to unity we get as a result the numbers of the series whose common ratio is 2; e.g. if to 1 is added 3 the result is 4. Conversely, if to 1 is added 2 the result is 3. Thus it is as if two lines were drawn intersecting each other like the Greek letter X.

§ 101. if we proceed further we return to the same numbers. For from 4 we go on to 8 and from 3 to 27; both series concluding with the same type of number, as though we were going round in a circle.

§ 102. We must realise that for Plato the more complex things found in nature are composed of simpler natures, just as the harmonies of sounds arise from the proportions between numbers. He put the essence of the soul mid-way between numbers, which are eminently abstract, and sensible substances; and so deduced the soul’s properties from the said numbers. Thus in the soul we find, first, a direct knowing, in that it looks directly at its object; and then the circular return by which the intellect reflects upon itself. So too the intellectual soul moves in a sort of circle with respect to the even and the odd in knowing things both like and unlike itself. And this principle is extended to the substance of the visible heavens moved by the World-Soul.

§ 103. For in the heavens we find two circular movements. One is simple and uniform by which the heavens move or revolve daily from east to west according to the equinoctial circle. The other is that of the planets, which is from west to east according to the circle of the zodiac, intersecting the equinoctial circle at the two points of solstice, i.e. at the beginning of Cancer and of Capricorn.

§ 104. And since the former motion is uniform, it is not divided into several motions; and in this it resembles the circle of the odd numbers; which is also why it is the greatest circle; for the odd numbers referred to are greater than the even.

§ 105. The second motion, however, is very much diversified, and seems therefore to answer to the circle of even numbers. It divides into seven circles according to the intervals between the numbers in the two series of multiples of 2 and of 3, as is said in the Timaeus. Where there are six points of division there must be seven parts divided off. Hence these circles are smaller and are contained by the highest circle which is that of the odd numbers. So the text is to be interpreted thus: ‘As the whole’, i.e. the Universe, is ‘borne along with well-attuned motions’, that is to say, as the harmonised movements of the heavens are due to the harmony of the World-Soul, God ‘bent the straight line into a circle’ in the manner described, according to the properties of number and of the soul; and dividing this one circle—one by the unity of the natural series of numbers, or by that of the intellectual power of the soul—into two, he forms the pair of numerical circles, the odd and the even, ,and the pair of circles in the soul, the understanding of moving and of motionless objects, and the pair of heavenly circles, the equinoctial and zodiacal motions.

§ 106. He adds, however, ‘adjusted at two points’, because any two intersecting circles touch each other at two points. And ‘again one’, i.e. the inferior one,’he divided into seven circles’, as if of the planets, ‘as though the heavenly motions were the soul’s motions, i.e. as if the heavens moved by the movement of the World-Soul.

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BOOK I, CHAPTER III, CONTINUED

SOUL AS A SPATIAL MAGNITUDE

CRITIQUE OF PLATO

Now in the first place it is not correct to say, that the soul is a magnitude. For that of the Whole he (Plato) regards as of the same nature as what is sometimes called mind, not as the sensitive or the appetitive soul; for the movement of these is not circular. Now mind is one and continuous, as is the act of understanding, which in turn consists of thoughts. But these have unity by succession, like number, not like extension. Therefore neither is mind thus continuous; but it is either indivisible, or not continuous in the way that anything extended is. §§ 107-11

How would it understand, if it were an extended quantity? As a whole, or by each of its parts? If by its parts, then by an extended part or by a point, if one may call a point a part. If by a point (of which there is an infinite, number) it is evident that it will. never complete the process. If by an extended part, it will understand the same thing many times over, even to infinity. Yet it seems to do so once for all. But if it is sufficient that it make contact with any one of its parts, why should it move in a circle or have any magnitude at all? But if it is necessary that it understand by contact with the whole of its circumference, what is the contact it makes by its parts? §§ 112-16

Again, how can the divisible be understood by the indivisible, or the indivisible by the divisible? § 117

It is necessary that intellect, be this circle; for as the movement of the intellect is to understand, and that of the circle is to revolve, if, then, understanding is a revolving, the intellect must be a circle whose revolving is thinking., But then it will always think something—since revolving goes on for ever. Practical thoughts, however, have limits, each being for the sake of something else; while speculative thinking likewise is limited by ideas and every idea is either a definition or a demonstration. But demonstrations begin from principles, and have as their term a conclusion or an inference. Even if they do not reach a conclusion, they do not come round again to their starting-point; they always take a new middle term and conclusion, and proceed straight forward. But revolving returns again to the beginning. Definitions too are all finite. §§ 118-21

Further, if the same revolving occurs many times over, there will be a multiple understanding of the same thing. §§ 122-4

Moreover, intelligence is better compared with stillness and rest than with motion,—and the same holds of logical deduction. §§ 123-6

Again, that will not be content which is not at ease but in a state of strain. But if movement is not of the essence of the soul, it will only move unnaturally. § 127

It must be burdensome for the soul to be entangled with the body without possibility of release; and indeed this should be shunned if it is better for the mind not to dwell in the body as is commonly said, and as seems true to many. § 128

It is not clear why the Heavens move by circular movement; for the essence of the soul is not the cause of the soul moving in a circle, for such movement is only incidental to soul. Still less is the body the cause, but rather the soul a cause for the body. Nor is this alleged as for the best; yet the reason why God made the soul revolve must have been because it is more worthy for it to move than to remain stationary, and to move in this way rather than in any other. But this speculation is better suited to other contexts, so let us now dismiss it. § 129

Another absurdity arises in this argument and in many others dealing with the soul. They conjoin body and soul, placing the soul in the body without stating anything definite as to the cause of this, or how the body is disposed. Yet this explanation is surely necessary, for it is in virtue of something in common that one is an agent, the other acted upon, one moves and the other is moved. No such correlations are to be found at random. These thinkers only endeavour to state what the soul is, without determining anything about the body which receives it, as if it happened that any soul entered any body, as in the fables of the Pythagoreans. For each body seems to have its own proper form and species. It is like saying that carpentry enters into flutes; for each art must use its tools, and the soul its body. §§ 130-1

ST. THOMAS’S COMMENTARY

LECTIO EIGHT

§ 107. Having stated Plato’s opinion, Aristotle now proceeds to its refutation. Here we should note that often, in criticising Plato, it is not precisely Plato’s own meaning that Aristotle criticises, but the obvious sense of his words. He has to do this because Plato’s method of teaching was faulty; he constantly used figures of speech, teaching by symbols and giving his words a meaning quite other than their literal sense; as when he calls the soul a circle. So lest anyone should be led astray by this literal sense, Aristotle sometimes argues precisely against it, in criticising Plato.

§ 108. Against the above-mentioned opinion, then, he brings ten arguments, some of which bear on Plato’s own view, and some on the literal sense of his words. Plato did not really mean that the intellect was anything quantitative or circular; he was talking metaphorically. Still, lest there should be any mistake about this, Aristotle argues on a literal interpretation of the words.

§ 109. In the first argument, then, he explains what ‘soul’ Plato had in mind, that it was the Soul of the Universe, and that ‘that’ (soul) which is ‘of the whole’, i.e. of the Universe, is exclusively intellectual, according to Plato. It is not vegetative, since it needs no nourishment; nor sensitive since it has no organs of sense; nor appetitive since appetite follows sensitivity. Indeed it could not in any sense be sensitive or appetitive, granted that the movement of the Universal Soul is circular; because neither sense nor appetite moves in a circle (for sense does not reflect upon itself) but. only the intellect (which does reflect upon itself, as when a man knows that he knows). So Plato concluded that the World-Soul was only intellectual, and said that intellect itself was a sort of spatial magnitude and a circle.

§ 110. Aristotle denies this, saying that Plato was wrong in representing the soul as a spatial magnitude circular in shape, and in dividing it into two circles.

§ 111. And he points out where Plato went astray. In this matter of the nature of the soul we have to base our judgement concerning any of its faculties upon the act or operation of that faculty, and our judgement concerning the act or operation upon the object of this act or operation; for faculties are known by their acts, and acts by their objects. Thus in the definition of a faculty is included its act, and in the definition of an act its object. Now it is clear that a thing gets its unity from whatever gives it being and specific nature. If then the intellect gets its being and specific nature from the intelligible which is its object (I speak of the intellect in act, which as such is nothing before the act of understanding occurs), it is clear that if it is one and continuous, as Plato held, it will be so in the same way as intelligible objects are one and continuous. For the intellect is one only in the same way as its operation (understanding) is one; and its operation is one only in the same way as its object is one; since acts are differentiated according to their objects. Since then the intellect’s object is intelligibles, and intelligibles compose a unity, not like a magnitude or a continuum, but like numbers which follow in a series, it is clear that the intellect is not, as Plato thought, a magnitude. It is either indivisible, as it is the nature of first principles to be, or, if it is continuous, it is so not as a magnitude but as number is; for as one number leads to another, so do we understand one object after another. And frequently several numbers terminate in one, as the premisses in a syllogism terminate in one conclusion.

§ 112. The second argument comes at ‘How would it understand’. For it might be answered that Plato’s reason for attributing magnitude to the intellect was not that there are many intelligibles, but that each intelligible by itself shows it to be a magnitude.

§ 113. But this will not do. For Plato maintained that the act of understanding was not a reception of intelligible forms into the mind, but a sort of contact (as of a circle, we have seen) due to the mind’s going out to meet intelligible forms. But I ask you, how precisely does the mind understand by contact, if it is a magnitude? it must touch its object either with the whole of itself or with a part. But if with the. whole of itself, then its parts are not needed and there is no necessity for supposing that the intellect is a magnitude or a circle. If, on the other hand, it touches with some of its parts, and thus understands in part, then either several of its parts are involved or only one. If only one, then again the other parts are superfluous and we need not suppose that the intellect has parts. But if it understands by touching with all its parts, these must be either points or quantities; and if points, then, since the number of points in any magnitude is infinite, the intellect would have to touch its object an infinity of times before it understood the latter at all; and thus it never would understand, since infinity cannot be traversed.

§ 114. Aristotle says ‘points’ not because he thought that a magnitude could be partitioned into points, but as disputing with Plato who regarded bodies as composed of planes, planes of lines, and lines of points; an opinion refuted by Aristotle in the Physics, Book VI, where it is shown that a point added to a point makes no difference.

§ 115. But if the mind understands by touching with quantitative parts, then, as each part is divisible into many, it must understand the same object many times over. Again, since any quantity is infinitely divisible into parts that are proportionately, not quantitatively, the same, it would follow that the mind understands the same thing an infinite number of times,—which raises difficulties. it would seem then that it touches its object once only, and that it cannot be called a magnitude, either with respect to many intelligibles or to only one.

§ 116. Notice that Aristotle is implying here that intellect is indivisible of its nature. What is intelligible in any thing is its essence or nature; which is present wholly in every part of it, as the specific nature is wholly present in each individual of the species; the whole nature of man in each individual man; and the individual as such is indivisible. Hence what is intelligible in anything is indivisible; and therefore so is the intellect.

§ 117. The third argument comes at ‘Again, how’. Granted that the mind is indivisible, we can easily see how it can understand both the indivisible and the divisible. It understands the indivisible in virtue of its own nature which is indivisible; and the divisible by abstracting from divisibility. But once allow, with Plato, that mind is divisible, it becomes impossible to understand how it can think of the indivisible. ‘Hence the difficulty of admitting Plato’s theory.

§ 118. The fourth argument begins at ‘It is necessary’. It runs thus. You say that intellect is circular and in movement. Now the movement of circles is a circling and that of the intellect is understanding; hence if intellect is a circle, understanding must be a circling. But this is false; for, since circular movement has no actual beginning or end, as is shown in the Physics, Book VIII, it would follow that understanding, the proper act of the intellect, never reached a term. But understanding has an actual beginning and end: hence it is not the same as circular movement, and therefore the intellect is not a circle.

§ 119. That understanding has an actual beginning and end can be proved in this way. All thinking is either practical or speculative. Clearly all practical thinking reaches a term or end; for it is all for the sake of something else, namely a work to be done, and in this work it terminates. And speculative thinking too has its proper end, namely ideas; for it always comes to rest in some idea: either, in a definition, when the mind simply apprehends something, or in demonstrations, when it combines and distinguishes things. But the first demonstrations begin from absolute first principles and terminate, in their turn, in the conclusions of syllogisms.

§ 120. If it be objected that one conclusion follows another, and thus there is no definite end, I answer that conclusions are nevertheless not circular. For, as is shown in the Posterior Analytics, Book I, demonstration cannot go in a circle; it always goes in a straight line; and an infinite movement or progression in a straight line is impossible.

§ 121. Definitions too have a beginning and an end, for you cannot go on to infinity in the enumeration of genera; the most general genus has to be taken as the first one. Similarly in enumerating species; you cannot particularise to infinity, but must stop at the most particular species. Hence the most general genus is the beginning, and the most particular species is the term or end, in definitions. Clearly, then, every act of the mind has an actual starting point and term.

§ 122. The fifth argument begins at ‘Further, if’. In a sense this argument depends on the previous one and is a part of it. It has been shown that if the intellect were a circle, as Plato thought, understanding would be a circling; and in the preceding argument Aristotle has shown that understanding is not a circling; which he now proves once more in the following way. The difference between a circular motion and any other motion lies in this, that the latter can never be repeated on the same quantity. This becomes clear if we think of the different kinds of movement in particular. Thus the movement of ‘alteration’ cannot be repeated in the same subject in the same respect; for the same thing is not in the same respect changed from white to black and black to white. So too in the movement of growth, the same thing cannot in the same respect both increase and diminish. So also in local movement; if this goes in a straight line it must have two actual terms; and if it is to be repeated, the term at the end of the movement must be used twice, once as end and once as beginning, and, since there must intervene a moment of rest at that term, it is not exactly the same movement. In circular motion alone can one and the same movement be many times repeated according to the same quantity; the reason being that in circular motion there are no actual terms; hence, no matter how often it is repeated, no interval of rest intervenes nor does the motion vary in any way.

§ 123. This being granted, Aristotle argues as follows. If you say that the intellect is a circle, then the act of thinking must be a circular motion. But this consequence is not admissible; therefore neither is the premiss.

§ 124. He then shows that the consequence is not admissible. Granted, he says, that the same circular movement is multiplied, that is, repeated, in the same respect. If thinking, then, is a circular movement, as you say, it will be repeated again and again as one and the same movement bearing upon one and the same object; and so the mind will think the same thing many times over. For the mind, in moving, touches and by this touching it thinks, as they say. If then its motion is circular it touches and thinks the same thing over and over again; which gives rise to difficulties.

§ 125. The sixth argument, at ‘Moreover, intelligence’ is as follows. if thinking is, as you say, a circular motion, it should be associated with movement, but in fact the contrary is true; thinking is associated rather with repose. This Aristotle himself teaches in Book VII of the Physics, where he says that if a man is to become wise he must first achieve an inward tranquillity; which is why the young and the restless are not, as a rule, wise. Wisdom and prudence are acquired, says Aristotle, by one who is content to sit down and be quiet.

§ 126. But lest it be said that, while this is true of simple apprehension, it is not true of syllogistic reasoning, he adds that reasoning also is more like a repose than a movement. Because, of course, before the syllogism is complete the mind and intellect are swaying from one conclusion to another and resting in neither; but when it is finished the mind holds on to one conclusion and rests in it.

§ 127. The seventh argument, at ‘Again, that, etc.’, runs as follows. Let us agree that thinking makes the soul happy. Now happiness cannot reside in anything violent or coercive, since it is the soul’s perfection and last end. As then movement is not of the soul’s essential nature, but is indeed alien to it, that operation in which the soul finds its happiness, namely, understanding, cannot be a movement, as Plato maintained. But that movement is not of the soul’s nature is implied by Plato’s own theory, for he said that the soul was first constituted by numbers, and then that it divide into two circles and was reflected into seven, from which followed movement. According to this view, then, movement is in the soul not naturally but accidentally.

§ 128. The eighth argument, at ‘It must be burdensome’, goes as follows. It seems to have been Plato’s view that it was not of the nature of the soul to be joined to the body; for he said that it was first constituted of the elements and then compacted with the body, so that it cannot leave the body at will. Well then; whenever one thing is united against its nature to another, and cannot leave it at will, the resulting state is painful; and whenever a thing deteriorates through its union with another thing the union is harmful and to be avoided. But ex hypothesi the union of soul and body is contrary to the soul’s nature; nor can the soul break away at will; and the result is bad for the Soul, as the Platonists are always saying. Apparently, then, union with the body is a painful and fearful thing for the soul; which hardly squares with Plato’s own theory that the soul is composed of elements and compacted with its body from the beginning.

§ 129. The ninth argument, at ‘It is not clear’, is as follows. Plato speaks of the Soul of the Universe and says it moves round in a circle. But this provides no explanation of the circular movement of the heavens; that is to say, it does not define the cause of it. For if the heavens move in a circle, this must be due either to intrinsic principles or to some extrinsic purpose. If intrinsic principles are the cause, the ‘nature’ in question will be either that of the soul or of the heavenly bodies. But it cannot be the soul’s nature, for circular movement is not of the essence of the soul, but is accidental to it; for, as we have said, the nature of the soul is to move in a straight line, which is then ‘bent into circles’. Nor can the cause be the nature of the heavenly bodies, for body as such is not the cause of the soul’s movements, but rather the soul of the body’s. But, if the cause is an extrinsic purpose, one cannot, on Plato’s principles, point to any definite end in answer to the question why the heavens move in a circle rather than in any other way; unless one brings in the will of God. God has indeed, for some reason, chosen to move the heavens rather than leave them motionless, and to move them in a circular way. But why he does this Plato cannot tell. However, as this matter belongs rather to ‘other contexts’, i.e. to another treatise (the De Coelo). We can leave it aside for the present.

§ 130. The tenth argument starts at ‘Another absurdity’. It is effective not only against Plato, but against many others also. It runs thus. It is dear that there must always be some proportion between mover and moved, agent and patient, form and matter. Not every form suits every body in the same way, nor does every agent act upon every patient. Nor, again, does every principle of movement move everything capable of receiving movement. There must be some correlation and proportion between them by which the one is naturally the mover, the other the moved in each case. Now obviously these philosophers admitted that the soul was in the body and moved it. Since then they spoke of the nature of the soul, it seems that they should also have had something to say about the nature of the body; about why the soul is joined to the body and how the body is related to and contrasts with the soul. Their study of the soul was inadequate so long as they discussed it alone and neglected to explain the nature of the body that receives it.

§ 131. Indeed, we may associate their thesis (Aristotle goes on to say) with the Pythagorean fable that any soul can enter any body; the soul of a fly for instance might perchance enter the body of an elephant. This cannot in fact happen; for the body of each particular thing, and especially of living things, has its own form and species and type of movement: hence there are great differences between the bodies of a worm, a dog, an elephant and a gnat. When they say that any soul can enter any body, it is as if one were to say that the art of weaving could enter flutes, or that the art of the coppersmith could enter a weaver’s loom. If it was in the power of these arts to enter bodies or instruments they would not do so indiscriminately, but the art of playing the flute would enter flutes, and not lyres, while the art of playing stringed instruments would enter stringed instruments and not flutes. In the same way, if there is a body for every soul, any soul does not enter any body; rather the soul shapes the body fit for itself; it does not enter a ready-made body. Plato and the others who speak only about the soul are too superficial; they fail to define which body answers to which soul, and the precise mode of existence of each in union with the other.

BOOK I, CHAPTER, IV

THEORY OF SOUL AS HARMONY

There is another opinion handed down about the soul, acceptable to many, and in no way inferior to the theories already discussed, yet chastised, as it were, and condemned, even in public discussions. For some call the soul a kind of harmony. §§ 132-3

And they say that harmony is a composition or tempering of opposites, and that the body is compounded of opposites. § 134

Yet a harmony is either a proportion in the components [of a compound] or the composition itself; and the soul cannot be either of these. § 135

Further [active] movement, which all attribute to the soul, does not pertain to harmony. § 136

It would be more appropriate to call health a harmony, and in general the powers of the body, rather than of the soul. This is evident if one tries to explain the passions and operations of the soul by some harmony: it is difficult indeed to correlate these! § 137

Further, we speak of harmony with two considerations in mind. Primarily as a correctly proportioned measurement, in what has motion and position, of component parts, so that nothing is missing that is becoming to them. secondly, the ratio of this composition. In neither way is this [predication of harmony to the soul] reasonable. The composition of the parts of the body is very easy to examine, for there are many and various such compositions. Of what and how can one suppose the mind to be a composition? Or sensation? Or appetite? It is no less absurd to account the soul the ratio of a composition. The synthesis of elements for bone is not the same as that for flesh. There would have to be many souls [in one body]; and indeed [a soul] for every body, if each is a mixture of elements, and the ratio of the mixture a harmony and a soul. §§ 138-40

One might at this point question Empedocles. He says that each of these exists in virtue of a proportion. Is this proportion then the soul; or is soul some other thing, thus inborn in the members? § 141

Or further: is concord the cause of any chance combination, or only of one based on some ratio? § 142

And whether this concord is the ratio of the composition or something else? These are the kinds of problem involved in this, hypothesis. § 143

But if the soul is other than the composition, why does it perish together with the essence of flesh and of other parts of the body? Moreover, granted that each of these parts has a soul, if the soul is not the ratio of the whole composition, what is it that is, corrupted when the soul departs? § 144

It is evident, then, from what has been said, that the soul cannot be a harmony, or move by revolving. It can, however, be moved and move itself, incidentally, in so far as what it dwells in moves and is moved by the soul. In no other way can it move in place. § 145

ST. THOMAS’S COMMENTARY

LECTIO NINE

§ 132. After rejecting Plato’s theory the Philosopher goes on to dispose of another opinion rather similar to Plato’s. For certain philosophers thought the soul was a harmony; agreeing so far with Plato’s view that the soul was composed of harmonic numbers; yet differing from him in that, while he spoke only of a numerical harmony, they extended the principle to include harmonies of compounds, mixtures and contrary qualities.

§ 133. First then he tells us, of a tradition handed down from the early philosophers concerning the soul, which seemed to contain some truth, not only about the soul, but about something common to all the principles of things. He says ‘something common’ because the early philosophers said nothing about formal causes treating only of material causes. Democritus and Empedocles were the two who seem to have come nearest to treating of the formal cause. The latter reduced everything to six principles, of which four—the elements—were material and two were formal, namely the part-active and part-passive principles, Concord and Strife. And the material elements were, they said, linked together by a certain proportion, whence they had a certain unity without which they could not exist together. And this proportion they called the form and harmony of things; whence it followed that, the soul was a harmony like other forms.

§ 134. Then, at ‘And they say that harmony,’ he states the ground of this opinion: harmony is the combination and mixing in due proportion of contraries in compounds and mixtures. The proportion itself is called harmony and is the form of the compound; and because the soul is a kind of form it was reckoned a harmony. Such was apparently the view of Dynarchus, Simiates and Empedocles.

§ 135. Next, at ‘Yet a harmony’, he begins to criticise it: first in a general way, and then, at ‘One might, etc.,’ with particular reference to Empedocles who formulated it.

The general theory is attacked with four arguments. The first is as follows. Harmony, strictly speaking, pertains to sounds, but is transferred by these philosophers to mean any due proportion, either in things composed of different parts or in mixtures of contrary elements. On this view, then, harmony is one of two things: either the compound or mixture itself, or the proportion existing in it. But the soul is clearly neither of these; therefore it is not a harmony. The reason why the soul cannot be, for these philosophers, either a compound or the proportion in a compound is that these are both accidental factors, whilst the soul, according to them, is a substance.

§ 136. The second argument begins at ‘Further, movement’. All philosophers agree that the soul moves something. But harmony does not move anything; rather it is a result and trace of movement, just as in music the movement of strings leaves its trace in harmonious sound. Similarly, the putting together and coadaptation of parts by some composing agent results in a certain proportional composition. If then the soul were a harmony resulting from some producer of harmony, we should have to posit another soul in the producer.

§ 137. The third argument comes at ‘It would be more appropriate’. In the Physics, Book IV, Aristotle had said that, if the definition of anything is to be adequate, it must answer to all that the given thing can do of itself or receive from other things; for the best definition states not only the substance and nature of a thing, but also its accidental qualities and capacities. If then the soul were a harmony, we ought to be able to work out its capacities and accidental qualities from our knowledge of this harmony. But this is extremely difficult; if, for example, we want to derive the operations of the soul from harmony, to what harmony does feeling or love, hating or understanding belong? It would be easier indeed to know the body through harmony. Thus we certainly can define good health as the duly proportioned and equally balanced commingling of the body’s humours; and likewise with other bodily qualities. Thus harmony belongs apparently to the body rather than to the soul.

§ 138. The fourth argument starts at ‘Further, we speak’. Harmony is sometimes found in things composed together and moving, when, that is, such things are so coapted and arranged that ‘nothing becoming to them is missing’, i.e. no defect occurs within the nature of the thing in question. The parts then are said to be well harmonised and the whole composition is called a harmony, e.g. of wood or stones or other natural bodies. In the same way when stringed. instruments or flutes are well-tuned, so that agreeable sounds result, they are said to be well harmonised. This is the proper meaning of the word. Sometimes, again, ‘harmony’ is found in mixtures of contraries; as, when contrary elements are so combined and mixed that no incompatibility remains, nor any excess of any one of them, e.g. of heat or cold or moisture or dryness; then they are said to be harmonised well and their ratio or proportion is called a harmony. So, if the soul is called a harmony it must be in one of these ways. But in fact it cannot rationally be so called in either of these ways. Those philosophers therefore spoke amiss.

§ 139. Clearly, the soul should not be called a harmony precisely in the sense in which compounds and compositions are harmonious. For in the body the interrelation of the various parts is quite evident; we can easily tell how the bones or the nerves are interrelated, what the arm is to the hand and the flesh to. the bone. On the other hand the principle according to which the parts of the soul are interrelated is obscure; nor does the correlation of parts in the body reveal to us how the parts of the soul, the understanding, and the senses, and desire, and so forth, are related to each other.

§ 140. Nor can the soul be called a harmony in the same way as the proportion in bodies compounded of a mixture of contrary qualities; and this for two reasons. One reason is that a different proportion is to be found in different parts of the living body; for the elements do not mix in the same ratio or proportion to form flesh as to form bone; and consequently there would be different souls for the different parts of the same living body, according to the proportional diversity and multiplication of its parts. The other reason is that all bodies are compounded of elements and contrary qualities; hence if the proportion of each compound is a harmony, and each harmony is a soul, there will be no body without a soul; which is an awkward thesis to maintain. It is not therefore of much use to call the soul a harmony.

§ 141. Next, at ‘One might at this point’, Aristotle attacks Empedocles by drawing three unforeseen consequences from his account of the matter. The first is this. If you maintain that every body has a certain ratio or proportion, which you call harmony and identify with the soul, I put the question to you whether the soul itself is this ratio or proportion, or something else. If you answer that it is the proportion itself, then, since in the same body there are different proportions for the different parts, two difficulties arise; there will be many souls in the same body; and there will be a soul for every compound. But if you answer that the soul is not the proportion itself, then, since harmony is proportion, the soul will not be a harmony.

§ 142.The second argument begins at ‘Or further’. Empedocles had asserted that the cause of union in things was Concord and the cause of disunion was Strife. Now union implies a certain proportion. I ask you, then, whether Concord is the cause of any and every union or only of such unions as are harmonious. If you answer ‘of every union’, then you must find sole cause other than Concord for the harmony and proportion proper to harmonious unions—unless you say that the latter occur by chance. But if you say that Concord is the cause of harmonious unions, then it is not the cause of all unions.

§ 143. The third argument, at ‘And whether this’, runs as follows. Empedocles says that Concord is what unites things. I ask: is Concord the same as the actual union in harmony, or is it not? If it is the same, then, since nothing causes itself, love cannot be the cause of the union as Empedocles asserted. But suppose it is not the same. Still, harmonious union as such is only a kind of agreement, which seems to be precisely what Concord is too. So they are the same after all; and the preceding argument applies as before.

§ 144. Proceeding, Aristotle shows how plausible is the theory in question. Its plausibility, he says, relies on the argument that if you grant one thing another must follow, and if you re move one thing another is removed. Thus when a body loses its harmony it loses its soul, and while its harmony remains the soul too remains. Yet the conclusion does not follow; for this kind of proportion is not, as those philosophers thought, the form itself, but only a disposition of the matter in view of the form. And if the harmony of a composite being is taken in this its proper sense, i.e. to mean a disposition, then the consequence is quite correct, that, so long as the matter’s disposition to the form remains, the form itself remains, and when the disposition goes, the form also goes. Not that the harmony is the form, but that it is a disposition of the matter in view of the form.

§ 145. Finally, where he says ‘It is evident, then’ Aristotle, concluding, summarises his rejection both of Plato’s view that the soul moves in a circle and of Empedocles that it is a harmony. The soul, as has been said, is moved indirectly, and it moves itself. That it is moved indirectly is clear, for it moves when its body moves; but the body itself receives movement from the soul. Only indirectly, and in no other way, does the soul move from place to place.

TEXT

408a34–408b31

BOOK I, CHAPTER, IV, CONTINUED

THEORY OF SOUL AS A SELF-MOVER RECONSIDERED

One might with more reason enquire about the soul as in movement by considering such facts as these: that it is, as we say, sad, pleased, confident, frightened; or again, that it is angry, feels and understands. All these seem to be movements; from which one might suppose that the soul moves. § 146

This, however, is not a necessary conclusion. Even if feeling pain or being glad or understanding are in the fullest sense movements, and each of these is a ‘being moved’ (e. a. being angry or fearful occurs by some movement of the heart), this being moved is from the soul. But as for understanding, it is either of such a nature or perhaps something other. §§ 147-50

Of these, however, some occur with a change of place in that which moves; others with an alteration,—of what sort or how is another question. To say that the soul is angry is like saying it builds or weaves. For it is perhaps better to say, not that the soul is compassionate, or learns, or understands, but a man by his soul. These modifications occur by movements not so much in the soul as, in some cases, proceeding to it, and in others, proceeding from it,as sensation proceeds from things, whilst remembering proceeds from the soul to the motions or rests which occur in the sensitive organs. §§ 151-62.

But intellect would seem to be a subsisting essence implanted in the soul, and not to corrupt. For it would corrupt [if it did], principally through the debility accompanying old age. But in fact what happens is similar to the case of the sensitive powers. If an old man could acquire the eye of a young man, I he would see as a young man; hence, senility is not an affliction of the soul, but of that which it inhabits, like drunkenness or disease. Understanding and thinking, then, decay with the decay of something else within. Understanding itself cannot be affected. But reasoning and loving and hating are not affections of the intellect, but of that which has it, precisely in so far as it has it. Wherefore, when this decays, the soul ceases to remember or love. For these proceeded, not from it, but from what was common, which has disintegrated. But perhaps intellect is something more godlike and unalterable.

Therefore, that the soul cannot be moved is manifest from these arguments. But if it cannot be moved, it is evident that it cannot be self-moving. §§ 163-7

ST. THOMAS’S COMMENTARY

LECTIO TEN

§ 146. After stating and criticising the arguments of those who thought that, because the soul moves the body, it must itself be in movement, the philosopher is next concerned to show that a stronger support for the assertion that the soul was in movement might be drawn from considering the activities proper to it. Dividing his treatment into two parts, he first states the hypothesis that the soul’s activities are evidence of its movement; and then settles the problem so far as his present purpose requires, this part beginning at ‘This, however’.

First, then, he says that whereas the philosophers, of whom he has been speaking, thought that the soul might be in movement from considering the fact that it moved the body, a more rational, i.e. a more plausible, argument might be drawn ‘by considering such facts as these’, i.e. as the activities of the soul itself. For from these one might build up a very plausible argument in favour of the soul’s being in movement. For we say that the soul ‘is sad, pleased, confident (i.e. daring) and frightened’; and we say that it gets angry and senses and understands. And since all these are activities of the soul, and also types of movement, it would seem that the soul moves. And this is a more plausible suggestion than the one already discussed. For the latter argued the soul’s movement from the body’s, according to the principle that every mover is itself moved; so that if soul moves body the soul itself is moved. But the theory now to be considered regards the movement of the soul from the standpoint of the soul’s own activities.

§ 147. Next, at ‘This, however,’ he clears up the difficulty. Here we should note that when Aristotle is searching for truth by a process of stating and answering objections, he will sometimes employ this method after having already demonstrated the truth in question; and then his objections and solutions are governed by the opinion he has already formed for himself. But sometimes he does all this before demonstrating the truth, and then he bases his objections and solutions on the views of others and not on his own opinion or on what he believes to be the truth. For example, in Book III of the Physics, where he argues against those who maintained the existence of an infinite, he employs a number of principles false in themselves but considered true by his opponents, e.g. that every body is both light and heavy. For he had not yet decided about the lightness and heaviness of bodies; this he did later on in the De Coelo, where, in consequence, he reopens the question of the infinite. And such is his method here. His criticism rests upon presupposing as true the views of his opponents.

§ 148. These latter, especially the Platonists, thought that sorrow, joy, anger, sensation and thought, and so forth, were movements in the soul, and that each of these activities, not excepting thought, had its own particular organ; so that in this respect there was no difference between sensitivity and intelligence; and every kind of soul, not the intellectual soul only, was immortal. All of which Aristotle concedes, presupposing that all such activities, even thinking, are organic, and that all souls are immortal. He only denies that such activities as sensation and joy are movements in the soul, asserting that they belong rather to the compound of body and soul. This alone he makes the point at issue.

§ 149. And here he does two things. First, he shows that the activities in question are not movements of the soul; secondly, he proves this with a special argument beginning at ‘But intellect’. His opponents, he says, maintain two points: (1) that joy and sorrow and so forth are movements; (2) that these movements are to be attributed to the soul; which therefore moves. But the conclusion does not necessarily follow; and in any case both propositions are false—the activities in question are not movements, nor are such things as anger, joy, sensation, to be attributed to the soul. But even granted, for the sake of argument, that they are movements, they should not be attributed to the soul; nor the soul , in consequence, be held to move in and with them.

§ 150. For it is obvious that; even if these activities are movements and are of the soul, they are not of the soul except with respect to certain definite parts of the body: thus sensation only takes place in certain parts of the body, such as the eye, the organ o sight; and anger in the heart; and so with the rest. it is clear that they are movements not of the soul alone, but of soul and body together. Yet they are from the soul; for example, when the soul thinks that anything is worthy of anger, the animal organ called the heart is disturbed and the blood gets heated around it. So also with fear; it makes a definite part of the body contract and change. And likewise with the rest. In these cases, then, the soul in itself does not move, but only moves in the movement of another thing, e.g. the heart. But in view of a point which Aristotle is going to prove later on, namely that understanding is an act of the soul alone, in which the body has no share, he observes here that perhaps understanding should be distinguished from all those activities which occur in the compound of soul and body. He says ‘perhaps’ because he is speaking tentatively. But in asserting that the other activities are of soul and body together he implies that they do arise from the soul.

§ 151. So, when he says ‘of these, etc.’ he means to show that these movements arise from the soul to the accompaniment of certain local changes; as in the case of anger, which occurs in the soul when parts of the body in and around the heart are moved: the blood heated by the heart is dispelled towards the extremities of the body. There may also be an ‘alteration’ or qualitative movement, as in fear, when the heart contracts and grows cold and one turns pale. What these passions are, and how they come about, is another question; but it is clear that as movements they are not in the soul alone, but in soul and body together.

§ 152. Hence just as any animal’s bodily activities spring not from its soul alone but from its body, or from the compound of soul and body, so too sense-perception and joy and so forth should not be attributed to the soul alone, but to body and soul together. To say that the soul gets angry and is thereby moved is like saying that the soul weaves or builds or plays the harp. The soul indeed is the cause of these activities; for the acquired ability to build or weave or play the harp is in the soul, and the exercise of the ability in each case springs from the soul. But, as it is better to say that the builder, not the art of building, builds, though the builder builds by his art, so perhaps it is better to say that it is not the soul that feels pity or learns or thinks, but the man who does these things with his soul. He says ‘perhaps etc.’ for the reason given above.

§ 153. But since the statement that the soul does not move, but man with his soul, might be taken to mean that movement exists in the soul as its subject, to forestall this Aristotle explains that when he says that man moves with his soul he means that movement is derived, as it were, from the soul, not that it is found in the soul itself

§ 154. For when I say ‘this moves with that’, my statement can be taken in two senses: either that the source of a given movement is itself moving, as when I say that a man moves with his feet, the feet themselves moving; or that something motionless in itself moves another thing; and it is in this latter sense that a man is said to move with his soul.

§ 155. Now this movement is two-fold. Sometimes the soul represents the term, to which the movement tends, as in sensation; for in the act of the soul’s apprehending exterior sense-objects, the sensitive faculty in the bodily organ is aroused and, moving, transmits ‘to it’, i.e. to the soul, images and notions of sensible things. But sometimes the soul behaves as the starting point of movement, as in remembering, when the latent, buried images and notions of things are brought to light, in order that sensible things may be understood through them. Whether the inward storing away of images should itself be called a movement or a resting is not immediately relevant.

§ 156. Movements of this sort, then, are not to be attributed to the soul, but to the soul and body together; if they spring from the soul, this does not imply movement in the soul.

§ 157. But observe that this solution of the problem is only provisional; it does not leave us with the truth perfectly defined. For movement is attributed to the soul’s activities in different ways by different people. In fact, three kinds of movement are discernible therein In some of these activities movement in the strict sense is found. In others it is found in a less exact sense of the term. And in others in a still looser sense.

§ 158. For movement proper occurs in the activities of the vegetative soul and in sensuous desire. In vegetative activity the material substance itself moves, in consequence of assimilating food. This movement is growth; wherein the vegetative soul plays the active part, the body a passive one. In sensuous desire also movement proper occurs, both through qualitative alterations and also through changes of place. No sooner does a man desire anything than he is affected by certain changes—becoming angry, as in the desire for revenge, or glad as in the pursuit of pleasure. And, accompanying this, the blood moves outwards from the heart to the extremities of the body; besides the fact that the whole man moves from one place to another in pursuit of what he desires.

§ 159. In a less strict sense, however, movement occurs in the acts of the sensitive soul. Here there is no movement of the material substance itself, but only a ‘spiritual’ movement of cognition: for example, the act of seeing is not a material modification; it is ‘spiritual’ reception into the eye of sensible forms. Yet it does involve some material change, because the faculty of sight is lodged in the body: and to this extent it involves movement, though it is not movement in the strict sense. Movement in the strict sense is not ascribed to the soul’s activities except when a modification of the material substance is the direct term of the activity.

§ 160. Least strictly of all, and indeed only by a metaphor, is movement to be ascribed to the act of the intellect, in which there is no movement of the material substance, as in the case of vegetative activities, nor even any alteration of the subject of ‘spiritual’ operations, as in the case of sense-awareness. There is only an activity which is called movement simply because the mind goes from potency into act. This differs from movement proper; for whereas the latter connotes an imperfection in the moving subject, this activity proceeds from the subject as already perfect and complete.

§ 161. Clearly then the acts of the vegetative and sensitive souls are not exclusively of the soul, but of soul and body together; while those of the intellect are only called movements metaphorically, and are exclusively of the soul, without the use of any particular bodily organ.

§ 162. Note too that, as desire and cognition are both found in the sensitive fart, the same division appears in the intellectual part also. Hence love, hatred, delight and so forth can be understood either as sensitive, and in this sense they are accompanied by a bodily movement; or as exclusively intellectual and volitional, without any accompanying sensuous desire; and understood in this sense they are not movements, for they involve no accompanying bodily change. In this latter sense they pertain even to immaterial substances, as will be shown more clearly later.

§ 163. Then, at ‘But intellect’, Aristotle sets out to prove what has been shown, namely that even if activities of this kind are movements (as the philosophers he is discussing maintained) still they are not movements of the soul alone, but involve the body also. So he takes one of their opinions (famous in his time), namely that not the intellect only, but every kind of soul without exception, is immortal. According to this view the intellect was a substance in the making, still incomplete, and was immortal. For it is a fact of experience that all the weakening and decay that affect the intellect or the senses come from the side of the bodily organ, not from the soul itself. Whence it would seem to follow that the intellect and every other sort of soul was incorruptible; if its activities grow feeble that does not imply its own decay, but the decay of the organs of the body.

§ 164. If the soul itself decayed it would decay especially in old age; that is when the organs of sense grow feeble. Yet in fact the soul itself is unaffected by old age; if an old man could be given a young man’s eye he would see just as well as a young man. The decline.,of old age, then, is not due to a decline in the soul or in the faculties of sense, but to the body; just as in sickness or drunkenness it is the body, not the soul, that is enfeebled. Hence ‘understanding’, i.e. simple apprehension, and thinking,’ i.e. the intellectual activity of combining and distinguishing ideas, grow weak, not through a weakness in the intellect, but through ‘the decay of something else within’, i.e. the intellect’s organ or instrument. Understanding ‘in itself cannot be affected’.

§ 165. Now in saying this Aristotle is not giving it as his opinion that the intellect has a special bodily organ, but, in the manner already explained, he is arguing on the supposition that the views of the philosophers whom he is criticising are sound; and it was their view, as we have seen, that each of the soul’s activities, and even intellect itself, had its special bodily organ. Assuming this, therefore, he gives as the reason for the decay of the understanding that it is one of those activities (like hating and loving) which are not of the soul alone, but of ‘that which has it’, i.e. of the compound of body and soul, or the bodily organ—precisely, he adds, in so far as this compound has ‘it’, i.e. understanding, and so forth. Consequently when ‘this’ (i.e. the bodily organ) ‘decays’ its activities, such as loving or understanding, decay likewise, and the soul itself neither remembers nor loves any more. The reason is that such processes did not only involve the soul, but that which was common’, i.e. the whole compound being; which has now decayed and passed away. Clearly, then, if all such movements and activities decay through the body’s decay, not the soul’s. they are not themselves exclusively of the soul, but of the soul and body together; and not the soul, but soul and body together, is what moves.

§ 166. But to remove any impression that he himself believes the intellect to be what the argument he is using supposes it to be, he adds these words, ‘Perhaps intellect is something more godlike and unalterable’, i.e. some sort of nobler power than any we are considering now, whose activity is exclusively of the soul. He says ‘perhaps’ because the question has not been decided yet; it will be cleared up in Book III. So much to show that he is arguing on a supposition.

§ 167. Finally, he concludes from all this that it is now clear that the soul itself cannot be the subject of movement. And if so, then the soul is obviously not a self-mover with movements of the kinds here discussed, as the philosophers he is criticising had maintained.

TEXT

408b32–409b18

BOOK I, CHAPTER IV, CONTINUED

SOUL AS A SELF-MOVING NUMBER

Much the most unreasonable thing said about the soul is that it is a number moving itself In this there are several impossibilities. First, what follows upon ‘being moved’, as they say; and then the special difficulties that follow their assertion that it is a number. How is one to conceive a unity, indivisible and undifferentiated in itself, as moving? Or by what? Or in what way? For if it is both moved and mover, there must be some difference in itself. §§ 168-9

Further, since they say that a line, being moved, makes a plane, and a point, being moved, a line, the movements of the units will be lines. Now a point is unit having position; so that the number of a soul must be in some place and have position. § 170

Further, if one subtracts from a number a number or a unit, another number is left. Plants, however, and many animals, live on after being divided, and seem to retain specifically the same soul. § 171

It would seem to be a matter of indifference whether one says ‘units’ or ‘small bodies’. For if the spheres of Democritus were to become points, and only quantity remained, there would remain in them a moving and a moved, as in extended matter, For the distinction spoken of is not due to largeness or smallness, but to quantity as such. Hence there must necessarily be something moving the units. But if it is the soul which moves the animal, so also in the case of number: then the soul is not a moving thing, which is also moved, but a mover only. § 172

Now this would have somehow to be a unit. If so, it must have some principle of differentiation from other units. But how can one isolated point differ from others, but in position? But if there are many different units and points in a body, they will be units in the same subject, and will occupy space as points. But, if there are two in the same place, what is there to prevent an infinity of them together? That of which the place is indivisible is itself such. But if the points in the body are the ‘numbers’ of the soul, or if the ‘number’ of body-points is that of the soul, why are there not souls in all bodies? For in all things there seem to be points, even to infinity. § 173

Furthermore, how is it possible for these points to be separated and released from the body? Since lines cannot be divided up into points? § 174

CHAPTER V

This amounts to saying (as we said before), either, under one aspect, the same as those who posit the soul. as a body of very refined elements, or, under another aspect, what Democritus said of the movement of the soul,—a thing intrinsically absurd. For if the soul is in all the body as sentient, there must be two bodies in the same place, if the soul is some sort of body. And for those who say it is a number, there are many points in one point, or else every body has a soul; unless the soul’s ‘number’ be other than that of the points in the body. The animal would then come to be moved by a number, precisely as Democritus said. What difference does it make whether one says small spheres or large units, or, in general, that units are in motion? In any case it must needs be that the animal moves when these are moving. §§ 175-6

These and many other consequences result for those who would combine number and movement in a single principle. It is impossible for such to be not only a definition of the soul, but even one of its accidents-as is clear if one attempts by this procedure to account for the soul’s activities and modifications, such as pleasure, pain and so forth. As we said before, on ihese principles it is not easy even to hazard a conjecture. § 177

ST. THOMAS’S COMMENTARY

LECTIO ELEVEN

§ 168. After refuting those who asserted that the soul was a thing that moved, the Philosopher goes on now to criticise the view of Xenocrates who said, in addition, that soul was a self-moving number; a far less rational opinion than the others already mentioned. For it involves many absurdities. First of course there are those arising from ‘being moved’, the irrationalities, namely into which all who say that the soul itself moves are led; and then, in addition, there are the special difficulties involved in the notion that soul is a number. Therefore in Xenocrates’ definition of soul the Philosopher criticises, not merely the terms employed, but the meaning itself. This critique has two parts. First he shows that the definition does not fit the soul itself or its substance; and then that ‘it does not fit its accidental qualities,—this at ‘These and many other consequences’. The former part subdivides into reasons for (a) rejecting the said definition and (b) for thinking that it involves all the difficulties implicit in the views of the other philosophers already criticised; this part beginning at ‘This amounts to saying’.

§ 169. He shows the unsuitability of the definition by six arguments; the first being as follows. You call the soul a self-moving number; but number is composed of units; the soul then, in your view, consists of units which move themselves. Now in any self-moving thing there are two parts (as is shown in Book VIII of the Physics), one moving, the other moved. Therefore you must mean that each unit or point is composed of two parts, one moving, the other moved. But this is impossible. Therefore the soul is not a self-moving number. To show the impossibility of a unit having a moving part and a moved part: what is wholly indivisible and undifferentiated cannot be thought of as moving itself in such a way that one part moves and another is moved. For the motive or moving factor and the mobile or moved factor cannot exist without differing. Since, then, the unit is indivisible and undifferentiated, it cannot have such parts as these. Therefore the soul is not a self-moving number.

§ 170. The second argument, at ‘Further, since’, runs thus. You say the soul is a number; and therefore composed of units, as has been said. Now the only difference between a unit and a point is that a point has position—it is a unit in position. But if the soul is a number, this number must exist somewhere in position. Therefore the soul is a unit in position, that is to say a point. But according to the Platonists a point in movement makes a line, a line in movement makes a surface, and a surface a body. If then the soul is a self-moving number each of its units is self-moving, and each of these is a self-moving point. But such a point can only make a line; therefore the same is true of the movement of the soul. Hence not life, but a line is the effect of the soul; which is not true. Therefore thesoul is not a self-moving number.

§ 171. The third argument, at ‘Further, if’, is the following. if, as you say, the soul is a number, it must have the nature and attributes of number. Now it is evident that whenever a unit is taken from or added to a number, the number is essentially changed. if you add 1 to 3 you alter the number in kind: 4 differs in kind from 3. Similarly if you take 1 from 3, leaving 2. Now it is agreed that living things are specified by their soul; since it is through the form that things are specified. if” then, the soul is a number, any addition to, or subtraction from, it must alter it in kind. But this is not true: for if plants and segmented animals are cut up the divisions go on living, the same in kind as before. Therefore the soul is not a self-moving number.

§ 172. The fourth argument, at ‘It would seem to be’ is as follows. You say the soul is a number; whence it follows, as we know, that it consists of units in position, i.e. points. But on this, supposition it is obvious that there is no difference between saying, with Democritus, that the soul consists of small indivisible bodies and saying that it is composed of units in position. For each unit in position is a quantity and indivisible.

Very well then; the soul, in your view, is a self-moving number and, consequently, consists of units and points moving themselves. Let us suppose then that the indivisible bodies of Democritus are points (there is no difference, as we have seen) and are quantities (as they must be, since only quantities, properly speaking, move). Now these points will move themselves if the soul is a self-moving number. But every self-mover, as has been said, is two-fold; hence each point itself is two-fold, having a moving part and a moved part; and this, no matter whether they be large parts or small, provided they have some quantity; for every self-moving continuum contains the two factors; a moving one and a moved one. So there must be a mover of the units. But in living things the mover is the soul; therefore the mover of the number would be the soul; whence it follows that the soul is not a moved but a mover, and thus, the definition of it as a self-moving number is incorrect. It should rather be defined as a number moving another number.

§ 173. The fifth argument begins at ‘Now this would have somehow to be a unit’. In Xenocrates’ opinion the soul is a unity. But if so, then it is a point; for it must, as a unity, differ from other unities and it cannot differ except through position. For what is it that differentiates ‘isolated points’, i.e. unities as here understood, excepting their position? Moreover, only through position are unities points. The soil, then, is not a mere unity, but a point. Yet it exists in the body and every body as such has its own points. Well then, are the soul-points identical with the body-points or not? If they are not, then every part of the body will contain also soul-points, and in every such part there will be two points at the same time in the same place. And if two, why not more than two, ad infinitum? Things whose place is indivisible are themselves indivisible; and require no increase of space if they increase in number; so, that if two can be in an indivisible place, there is no reason why an infinite number should not be there. On the other hand if body-points are identical with soul-points, then every body has a soul, since every body has points. But this is false; therefore the soul is not a self-moving number.

§ 174. The sixth argument, at ‘Furthermore, how’, continues the preceding one. It follows from Xenocrates’ theory that the soul is composed of points. Points are obviously inseparable and undetachable from bodies; for lines are not separable from surfaces, nor points from lines. But this is not true of the soul; hence it is not a point or a number. Clearly then, Xenocrates’ definition is intrinsically inappropriate.

§175. Then, at ‘This amounts to saying,’ he finds this definition objectionable in its consequences. These consequences involve all the objectionable consequences flowing from the theories of all who have philosophised about the soul. For some of these fell into the mistake of saying that the soul was a body made up of extremely fine parts, whence it would follow that two bodies would be together in the same place; for the soul is wherever sensation occurs, and this is everywhere in the body. And the same would follow, as has been said, if the soul were composed of points: two points, or even an infinite number of points, would exist together in the same place at the same time. This would follow if the soul-points differed from body-points. And if ‘the number be other’, i.e. if there is no difference between soul-points and body-points, then every body contains a soul, since it must contain points.

§ 176. Others, like Democritus erred in saying that the soul itself moved, and the body because of the soul. And from Democritus’ statement that the soul was made up of indivisible spheres whose movement caused the body to move it followed that indivisible bodies were the cause of bodily movements. The same difficulty follows from the definition which states that an animal is moved by a number and so by points. It makes no difference what size we give to the moving spheres or units; for ‘in any case’, i.e. with spheres or with units, the origin of the soul’s movement is the movement of bodily spheres and points.

§ 177. Next, at ‘These and etc.,’ he shows the weakness of the above definition with respect to accidental qualities. A complete definition, he says, must give knowledge of the accidents as well as of the substance of the thing defined. But if we combine number and movement in our definition of the soul, we shall find ourselves involved in many difficulties besides those that concern the soul’s substance. For these two things, number and movement, not only cannot belong to the substance of the soul, but are not even accidental qualities of it, nor are they means to a knowledge of these qualities. Hence the definition itself is unsuitable; it does not help us to know the accidental qualities of the thing defined. This will be evident to anyone who, relying on this definition, tries to attribute to the soul affections and activities such as reasoning, pleasure, pain and the like. If we started from number and movement, we should not only find it, hard to reach any knowledge of the soul’s accidental qualities and passions and activities, but we could not even begin to hazard any conjecture about them.

TEXT

409b18–411a7

BOOK I, CHAPTER V, CONTINUED

EMPEDOCLES’S THEORY OF COGNITION

SOUL NOT COMPOSED OF THE ELEMENTS

There are, then, three ways in which men have defined the soul: some declaring that it is the principal mover, being self-moving; some, that it is the most subtle of bodies, or the least corporeal of things (what contradictions and problems these views entail we have briefly reviewed); so what is left for us to consider is how it is said to be constituted from the elements. They say this is so because the soul perceives things that are and knows each one. But many irrational consequences follow upon this. For they suppose that like is known by like, as if they meant to identify things themselves with the soul. But those [elements] are not the only things; there are many others, perhaps infinite in number, derived from them.

Granted, then, that the soul knows and perceives the elements of which each of these is formed, yet it will not know or perceive wholes, such as what a divinity is, or a man, or flesh, or bone, or anything else compounded. For the elements of these are not interrelated at random, but by some ratio or principle of composition, as Empedocles said of bone,

The earth all gracious in its ample caverns

Took two parts out of eight of water and light,

But four from the god of fire, and then

White bone was made.

So it is no use supposing elements to be in the soul unless there are in it also principles and co-ordination. Let each know its like, it will not know bone or man unless these be in it. It is hardly necessary to say, however, that this is impossible; who would ever think of enquiring if there is a stone in the soul, or a man? Likewise, the good or the not-good; and similarly with other things. §§ 178-80

Further, ‘that which is’ can be predicated in several ways: in one way, substance, in another, quality, in another, quantity; and in any other way according to the categories that have been distinguished. Will the soul be made up of all these or no? But it does not seem that there are elements common to all these. is it from those of substance only? How then will it know anything of the other kinds? Or is one to say that there are elements and principles proper to each category of which the soul is composed? then there will be quality and quantity and substance in the soul. But it is impossible that of the elements of quantity be derived substance, and not quantity. For those who hold that the soul is composed of all things, these (and other such) difficulties arise. §§ 181-2

It is unreasonable to say that one thing cannot be acted on by its like, and yet that sensation and knowledge is ‘like by like’. For they posit sensation as being moved and affected, and knowing and understanding likewise. § 183

What has now been said witnesses to the many difficulties and doubts to be faced by one who, with Empedocles, says that each thing is known through its corporeal elements and [their relation] to its likeness. For whatever things in the body are obviously earthy (bones, sinews, hair) seem to perceive nothing; nor therefore even their likenesses; and yet they ought [on this hypothesis]. § 184

Again, each one of the principles will have more ignorance than understanding. For it will know a single principle and be ignorant of many others, indeed of all others. § 185

Further, for Empedocles, the Divinity must be the least knowing of all things, for he alone will not know one of the elements, namely Strife; but mortals, all; for every individual is composed of all. § 186

In general then, why is it that everything has not a soul? For all things are either elements or are made of one, or of several, or of all. They ought accordingly to know one, or several, or all. § 187

One might wonder what gives unity to them. For the elements are comparable to matter, and that which holds them together, whatever it is, is the most essential principle. That it should have a higher function or be more excellent than the soul is impossible; still more impossible that it be higher than intellect. For that this is the primordial and most exalted and godlike thing by nature is in full accord with reason. Yet these men say that the elements have priority among beings. § 188

Not one of those who maintain that the soul is constituted from elements because it perceives and knows realities, and that it is primary among moving forces, considers every kind of soul. For not all sentient beings move; for certain species of animals are observed to remain in one place, although it would seem that the soul moved the animal with this one motion only [i.e. locally]. Likewise with those who would make of elements the sensitive and intellectual powers; for plants seem to live, but are not endowed with local motion or perception; and many animals lack intelligence. Even setting this fact on one side, and admitting that intellect is a part of the soul, and the sensitive power likewise, they would not be speaking of every soul, nor of the whole of any soul, nor of one [entire soul]. The same objection tells against a notion expressed in the Orphic hymns, where it is said, ‘The soul enters from the universe, breathed in by the winds.’ This cannot occur in the case of plants and certain animals: unless, indeed, all use respiration; a fact overlooked by those who put forward this view. §§ 189-90

But if one must constitute the soul from the elements, there is no need to use them all; for one term of contraries suffices for the discernment of itself and its opposite; thus by the straight line we know both itself and the oblique; the criterion of both is the rule, but the curved is a criterion neither of itself nor of the straight.

ST. THOMAS COMMENTARY

LECTIO TWELVE

§ 178. Having in the preceding sections explained that the early philosophers pursued their enquiry into the soul by three ways, that of movement, of knowledge and of incorporeal being, and having pressed certain objections against those who took the way of movement, and against those who identified soul with something bodiless and entirely simple, the Philosopher now turns to criticise the upholders of the principle that the soul knows everything because everything is included in itself.

§ 179. With their theory that all knowledge takes place by means of assimilation these philosophers had caught, as it were, a far-off glimpse of the truth; but they expressed this by saying that the reason why the soul knew all things was that all things entered into its composition, and that the soul possessed the likeness of all things according to the mode of existence, i.e. a corporeal one, which things have in themselves outside it. Hence, if things consist of elements, the same is true, they said, of the soul; and that is the cause of sensation and knowledge. The chief upholder of this view was Empedocles, who posited more elements in the soul than anyone else; and therefore the Philosopher is more concerned here to refute him than anyone else. So he first attacks the opinion of Empedocles, and only then, at ‘And some say’ that of certain others.

§ 180. Against Empedocles he brings ten arguments. The first is as follows. Empedocles argues that the soul must be composed of all the objects of its knowledge because knowledge takes place by means of similitude. But this involves many difficulties and absurdities. For clearly the elements are not all that any given thing contains; it includes much else besides, such as the proportion in which its elements are combined and the formulable essence of each one in particular, and there may even be an infinity of accidents belonging to things made up of elements. Take, for example, bones. To understand bones we need to know, not only the elements of which they are composed, but also how these elements combine in them, and the functional pattern of bones; for the order of elements in compound things is not a random one, it involves a certain definite proportional arrangement. If bone, as Empedocles says, is composed of eight parts, each bone has eight parts into which the various elements enter in unequal measure: for earth, he says, contributes two parts, air and water one each, and fire four—to which predominance of fire is due the whiteness of bone, while from earth comes its dryness. Thus in compound things there are, besides the elements, certain proportions and patterns. Well then, either these proportions are in the soul together with the elements, or not. If they are in the soul, then bones and flesh and so forth, and therefore men and stones and bodies and things quite contrary to one another, are all in the soul; and this nobody dreams of conceding. But if only the elements are in the soul, then it does not in fact know the proportion in things nor compound things as such; and how can it know God (i.e. the Heavens as a whole) or man or stone or bone? It cannot possibly know these things; it knows only the elements which compose them, according to this view.

§ 181. The second argument, starting at ‘Further, that which is’, runs thus. You say the soul is made up of elementary principles. But these differ according to the different categories of things, such as substance, quality, quantity and the rest. Is then the soul made up of the elementary principles of substance alone, or does it include those of the other categories? If the first alternative is right, then the soul only knows substance; yet the supposition is that it knows everything. But if it includes the elements of all the categories, then, since whatever has the elementary principles of substance is a substance, and whatever has those of quantity is a quantity, and so on likewise with the rest, it follows that the soul is at once both a substance, and a quality, and a relation, and so on and so forth.

§ 182. It might be answered that the elementary principles of substance are also those of quantity, quality, etc., since everything is grounded in substance; hence the soul need only possess the principles of substance to know everything. But I say that things have both remote and proximate principles, and should be known by means of the latter. The principles of substance may be the remote, but they are not the proximate, principles of the other categories; hence they cannot give knowledge of anything except substance.

§ 183. The third argument, starting at ‘It is unreasonable’, is this. The reason why the soul is said to be composed of all the elements is that it knows all things and knowledge is by similarity. Against this is the admitted fact that sensation and knowledge are a sort of being acted upon; and it seems unreasonable to say that like is acted upon by like, and not rather by its contrary; and consequently, to say that sensation or knowledge are by similarity.

§ 184. The fourth argument, at ‘What has now’, is this. What has been said already is enough to show that Empedocles’s theory is highly questionable and his manner of expressing it slipshod. But there is a yet stronger objection. If the soul, as he says, knows by similarity, then the element air Will know air, and so on for the other elements. But we know that animals’ bodies have many earthy parts which lack sensation, such as hair, bones and nerves; yet they ought to have sensation according to this theory. Therefore knowledge is not by similarity nor the soul composed of the elements.

§ 185. The fifth argument’s at ‘Again etc.’, runs thus. Another objection to this view is that it implies that principles as such are more ignorant than percipient. For if knowledge is only by similarity, and if every principle is quite simple, having no likeness to anything but itself, it follows that each principle only knows itself and is ignorant of everything else.

§ 186. The sixth argument comes at ‘Further’. This theory also implies the doubtful consequence that God is the most ignorant of all living beings. For, as we have seen, Empedocles thought that everything on this earth could be reduced to the four elements together with Strife and Friendship, these last being the causes of coming-to-be and passing-away. But the sky he called God and said it was composed of the four elements and Friendship, but not of Strife; and was therefore incorruptible. If then knowledge is by similarity, God cannot know Strife, since it does not form part of him, and God is therefore less percipient, strictly speaking, than other living beings which know Strife because they include it.

§ 187. The seventh argument’ comes at ‘In general, why’. If the soul is made of all the elements, then all things have souls; for all things are made of either all or some elements. Now whatever is made up of elements or of compounds of elements is a body. Hence all bodies, indeed all beings, have souls; which is false.

§ 188. The eighth argument’ begins at ‘One might wonder’. The elements are many and contrary; but whenever contrary things come together in a composition there must be some other thing which includes and unifies them. Hence if the soul is made up of the elements there must be something in it which unifies them. But it is extremely doubtful what this can be; for it must be something in the soul nobler than the soul, which is an impossibility, at least as regards that, which it is reasonable to consider the supremely noble and divine thing, namely the mind. Besides, this other thing would have to be prior to the elements, whereas Empedocles and the rest have asserted that the elements were the first of all beings. Therefore the soul is not made up of elements.

§ 189. He begins the ninth argument at ‘Not one of those’, showing the weakness of Empedocles’s view and that of all the others who have enquired about the soul, whether by way of movement or by way of sense-perception. For (1) there is a gap in the arguments of all who defined the soul in terms of local movement. Many living beings, such as plants and things resembling plants, do not move locally at all but are fixed in one place. And (2) there is a like inadequacy in the definition of the soul in terms of intellect or sensation; for plenty of living things neither sense nor think. And if local motion, intellect and sensation are taken separately and regarded as distinct parts of the one soul, this will not apply to soul in general, since not all souls are intellectual; nor to the whole of any one soul, since only parts of it will be intellectual and sensitive; nor to any one single soul, since this description does not enumerate all the characteristics of any given soul; for in any soul there are other things besides understanding and sensation.

§ 190. And a certain philosopher named Orpheus having fallen into a rather similar error in what he said about the soul, he too is mentioned here. Orpheus was one of those three early thinkers who were, so to say, poet-theologians; for they wrote in verse on philosophy and about God. The other two were Museus and a certain Linus. Orpheus, a wonderful orator whose words had power to civilise wild and brutish folk, was the first man to induce his fellows to five together in society. For this reason it is said of him that he could make rocks dance to the sweet sounds of his harp, which really means that his eloquence could melt the hardest hearts. And after these three poet-philosophers came the seven sages, of whom Thales was one. Now this Orpheus thought that the whole air was alive, was indeed a sort of living soul, and that the so-called souls of living bodies were really nothing but the air these bodies breathed; and this idea he expressed in verse. But the Philosopher objects to the Orphic theory, saying that it is just as inadequate as the others he has criticised; for there are many animals that do not breathe at all, ‘a fact’, he says, ‘which was overlooked’ by those who held this opinion. The criticism touches the inadequacy of the theory.

§ 191. At ‘But if one’ comes the tenth argument; which convicts the Empedoclean theory of unnecessary complication. The soul’s capacity for knowledge is explained by its composition from elements. Now it is a matter of experience that knowledge of anything rests on few, rather than many, principles-, hence even if we grant that the soul is composed of elements we ought not to suppose that these are all the elements, but at the most two. And that knowledge rests on few rather than many principles is clear if we consider that in composite things, consisting of two principles, one of perfection, the other of imperfection, it is in the light of the former that we know the latter; and that in contraries, which can be reduced to a quality and its privation, it suffices to understand the term denoting quality and perfection in order to understand also the other term denoting privation and imperfection. Thus by, the idea of straight line we know and for in judgements about both straight and crooked lines; for ‘the rule’, i.e. the measure, is the means of knowing both; but the crooked line is the means of knowing neither itself nor the straight. Hence there was no need to regard the soul as made up of all the elements; enough to adduce two only, fire and earth, as its means of knowing both itself and contrary things. Through fire it could know both cold and hot objects, and through earth the dry and the moist.

TEXT

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BOOK I, CHAPTER V, CONTINUED

THE ELEMENTS HAVE NO SOUL

And some say that the soul is intermingled generally with the Universe. That is perhaps why Thales thought that the whole world was full of divinities. § 192

This, however, involves several difficulties. For why does the soul in fire and air not result in an animated being, whereas it does so in composite beings?—and that, even though it is thought to be more excellent in the former. (And one might well query why the soul in the air should be nobler and more enduring than that in animals.) On either count the theory is absurd and unreasonable. To say that air or fire is an animal is among the most wanton of absurdities; and if there is a soul in them, it is inconsistent not to call them animals. §§ 193-5

They seem to have held that there was a soul in these on the ground that the Universe is made up of homogeneous parts; so that if animals become animate by partaking of the containing element, they must say that the soul [of the Whole] is homogeneous with its parts. § 196

If then the air, divided off thus, be homogeneous, but the soul be composed of heterogeneous parts, something of it [the soul] will exist and something not. It is necessary then, either that it be of homogeneous parts, or that it be not in any and every part of the whole. § 197

It is evident then, from what has been said, that the cause of knowledge being in the soul is not that soul is made up of the elements; and that it is neither true nor apposite to say that it is in motion. § 198

I That the distinction here referred to between parts of ‘soul’ refers to mortal and immortal existence is St. Thomas’s interpretation of this passage (§ 197).

ST. THOMAS’S COMMENTARY

LECTIO THIRTEEN

§ 192. Having stated and rejected the theories and arguments of those who maintained that the soul was composed of elements, the Philosopher is now led, by the same train of thought, to discuss the notion, upheld by some, according to which a soul is intermingled with the elements. First, then, he states this opinion, and then, at ‘They seemed to have held’, the argument used to support it. And the opinion itself is first stated and then, at ‘This, however,’ attacked.

There are, he says, some who see a soul intermingled with everything, whether simple elements or things composed of these. This perhaps is what Thales meant when he said that everything was full of gods; perhaps he thought that the entire Universe was alive and its life was divine; that just as soul exists everywhere in each living thing so a god was everywhere in the Universe and everything therefore was ‘full of divinities’. And perhaps this was the notion that underlay idolatry.

§ 193, At ‘This, however,’ he points out, against this opinion, that it presents certain difficulties. For instance, if a soul exists in air and in fire (and of these two especially this was asserted) it is hard to see why it does not make ‘animated beings’ of them, i.e. why air and fire are not animals. Things composed of several elements are animals precisely because they contain a soul; and one would expect the soul to be all the more powerful where the element is pure and simple.

§ 194. Again , one might ask, he says, why the soul which they place in the elements should be considered higher and more immortal than the soul of things composed of elements. For the latter constitute knowing, sentient animals; not so the former.

§ 195. But, however the objections are put, the result is damaging to this theory. To say that fire or air is a living body is most improbable in itself; it is contradicted by experience; and is unsupported by any good reason. And to deny that things which have souls need be living bodies is most unreasonable; for it would follow that there was no difference between souls that exist in bodies and those that do not.

§ 196. Then, at ‘They seem to have held’, he states the reason used in support of this theory and refutes it; after which, at ‘It is... evident’ he draws a general conclusion from all the foregoing discussions. The reason, he says, why some philosophers seem to have thought that a soul existed in ‘these’, i.e. in all the elements, was that they thought that the whole and the parts in elements were of the same nature, since the elements are simple. Observing that that part of ‘the containing element’, i.e. the air, which came into contact with the bodies of animals through their breathing, was the cause and principle of animal life, they thought it necessary to conclude that the soul of the whole was ‘of the same specific nature as the parts’, that is to say, that all the containing air was alive.

§ 197. At ‘If then’ he refutes this argument. The assumption is that, because the portion of the air removed and inhaled by an animal is of a like nature to the air as a whole, the soul of the animal itself is, as it were, a portion of the soul of the whole air. But on their own principle this is clearly false; for, according to them, the soul of air ‘exists’, i.e. is immortal, as that which has never ceased from vivifying animate beings, whereas the soul of this or that particular animal ‘does not exist’, i.e. is not immortal. Therefore either of two awkward consequences flow from this theory. If all the parts of air, those outside and those breathed in, are homogeneous, then the same is true of the soul; but this has been disproved. But if the soul’s parts are heterogeneous while the air’s are homogeneous, then the soul is not in every part ‘of the whole’, i.e. of the whole air; which is against those who said that all the air had a soul.

§ 198. Then at ‘It is evident’ Aristotle concludes this part of the discussion of earlier opinions. Neither of these two predications made’ by the ancients was, he says, either true or well-expressed; namely that knowledge in the soul is a consequence of its being composed of elements, and that movement is in it for the same reason. So much should be clear to anyone who has followed the discussion up to the present.

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BOOK I, CHAPTER V, CONTINUED

THE UNITY OF THE SOUL

Since knowledge pertains to the soul, and sensation, and thinking, as well as desiring and deliberating—in a word, all appetition; and as in animate beings there also occur local motion, and growth, and preservation, and decay, all from the soul, is each of these in the whole soul, and do we understand and perceive and do and undergo every particular experience, with the whole soul? Or does each require a different part? And is life itself in any one of these? Or in several? Or in all? Or is it from some quite distinct cause? §§ 199-203

Some say the soul is divisible, understanding by one part and desiring by another. §§ 204-5

If then the soul is of its very nature divisible, what holds it together? Not the body, certainly: much rather the contrary seems to be true, that the soul holds the body together; for when it departs, the body expires and decomposes. If there is some other thing which makes it one, this other is rather the soul. One would then have to ask, concerning this other, whether it be one or of many parts. If it is one, why not call it the soul straightway? But if it is divisible, reason again demands, what it is that holds this together? And so on ad infinitum. § 206

A further query arises about the soul’s parts: what power has each in the body? if the whole soul holds together the whole body, it would be fitting if each of the parts controlled some part of the body. But this looks like an impossibility. It is difficult even to imagine what part the intellect would hold together, or how. § 207

It is also held that plants live after being divided, and certain divided animals also; as if they had a soul specifically one, but not numerically. For each of these parts is endowed with sensation and moves locally for a certain time. If they are not long-lived, that is no objection: they have not the organs. requisite for the preservation of their natures. Nevertheless, in each of the parts are to be found all the parts of the soul; and those separated parts are specifically the same as each other and as the whole; as each other, as if they were not separable; as the whole, as having an indivisible unity. § 208

It would seem that the principle in plants is some sort of soul. Plants have only this in common with animals, and while this is independent of the sensitive principle, nothing has sensation without having this. §§ 209-10

ST. THOMAS’S COMMENTARY

LECTIO FOURTEEN

§ 199. Having reviewed and criticised earlier opinions on the soul the Philosopher proceeds now to put certain questions of his own; which at ‘Some say’ he begins to answer. But first we have to realise that the activities, of the soul, such as sensation, understanding, desire, movement in space, and growth, can be considered in two distinct ways. We can consider the mode of these activities; and from this point of view we can distinguish, underlying these activities, three powers of the soul: the vegetative, the sensitive and the intellectual.

§ 200. And these powers differ. For whilst the vegetative or nutritive power acts through active and passive qualities of matter, such as heat and cold and the like, the sensitive power requires no such sensible qualities for its sentient activity, though it does depend on corporeal organs; while the intellectual power acts through neither sensible qualities nor a corporeal organ, for it functions in an entirely incorporeal way.

§ 201. But if we consider the kinds of activities within the soul’s range, then we distinguish five powers with five corresponding activities: the nutritive, sensitive, locomotive, appetitive and intellectual powers.

§ 202. Having then discussed and criticised earlier opinions on the soul in general, Aristotle begins now an enquiry into the parts and particular activities of the soul. And he proposes two problems. The first is whether activities like sensing, rational judgement, desiring, deliberating, and also appetition (which he related to special parts of the soul in a more general way than these, placing the irascible urge in both the sensitive and the rational parts), together with local motion and rest, growth and decline, whether all these pertain to the whole soul in such a way that each one occurs in every part of the soul, so that with each part we both understand and sense and move and desire and assimilate food; or whether the truth is not rather that each activity has its own special part, that is to Say, that with one part we understand, with another we sense, and so on

§ 203. The second problem is this. Granted that each activity has its special part of the soul, is this true of the activity of simply being alive? Is this activity proper to any one of these parts? Or to many? Or to all at once? Or does it perhaps belong to some other part?

§ 204. Then at ‘Some say’ he answers these questions in order. As to the first one, he states and then rejects a view of certain philosophers that the activities in question spring severally from the soul’s parts, ilot from the soul in general; that the soul is so divided into parts that it understands with one and desires with another, just as some people hold that the sensitive power is in the brain and the vital power in the heart, and so on.

§ 205. Now this is partly true and partly false. if you take it to mean that the soul has different parts potentially, it is quite true that its parts and powers are distinct and that one of them understands and another senses. The soul is a whole in the sense that it has a total capacity with partial capacities subordinate to the whole. But if you take it quantitatively, as though the soul were of a certain size with parts of certain sizes, then this opinion is false. And this was how the philosophers in question thought of the soul—even to the extent that they made out the soul’s different powers to be different souls.

§ 206. Next, at ‘If then the soul’, Aristotle attacks this last hypothesis, with three arguments. The, first is this. Different things cannot be unified except by something else that unites them. If the one body contained several souls, these would have to be joined together and contained by something else. But there is nothing else that can do this; therefore the hypothesis is groundless. That there is no other unifying principle is shown thus. Whatever contains and unifies the soul will be either the body or some other thing. Now it is not the body. Rather, the body is contained and unified by its soul and falls to pieces when the soul leaves it. Then it is something else; but this must be a soul if it pertains especially the soul to unify and control. Is then this unifying soul itself intrinsically one, or made of several parts? If of several parts, then what unites them? And so on ad infinitum. But if this unifying soul is intrinsically one, then ‘why not call it the soul straight away’, i.e. why not concede at the beginning that the soul is intrinsically one? The soul, then, is not, as they thought, quantitatively divisible.

§ 207. The second argument comes at ‘A further query’. If the different parts of the soul are in different parts of the body, then each soul-activity has its own corporeal part or organ. But the intellect has no special corporeal organ. Hence their conception of the soul’s parts is false.

§ 208. The third argument starts at ‘It is also held’. If each of the various activities of soul is proper to a special part of the body, then no one part is the organ of several distinct activities, nor are there several parts ‘in an animal’ body the same in kind. But experience proves that certain living things have parts with several activities each, and a soul that is identical in kind in the whole and in all the parts; e.g. in plants and in certain (segmented) animals ‘ which go on living after being cut up, the cut off parts retaining their feelings and movement for some time. It does not matter if these parts live for only a short time through lack of the organs of self-preservation. The point is that several soul-activities exist in several distinct corporeal parts at once, and the latter are specifically similar to each other and to the whole. Therefore the soul is not divided according to the different parts of the body.

The reason why such animals go on living after being divided is that the number and diversity of activities complete in themselves varies in direct proportion to the perfection of the soul in living things. The higher the soul, the wider is the range of its activities; and the wider its active range the more, and the more distinctly diversified, organs or bodily instruments are required by it. So the relatively greater nobility of the rational soul calls for a greater diversity of its bodily organs, whilst the far lower soul of a segmented animal or a plant has only a narrow field of activity and therefore needs a body that is more uniform and less articulated, and in any part of which, taken separately, it can maintain its being.

§ 209. Then, at ‘It would seem’, he answers the second question; concerning which we must realise that life belongs, properly speaking, to things that move and act of themselves and are not caused to do so by others. So ‘to live’ has two meanings. It can mean the being of a living thing, and in this sense Aristotle says that living is the being of living things. And also it can mean activity.

§ 210. Now the soul of plants, the vegetative soul, seems to be a sort of primary manifestation of life among things here on earth; for nothing lives without it and all living things share in it, though in other ways their modes of life differ. Animals and plants have only this in common. It can exist without sense or intelligence, but not sense or intelligence without it; no animal has sense or reason except it first have vegetative life. Thus it bears the same relation to life as touch to sensation. Not that living things only live by this principle, but it is the point where life first appears.

BOOK TWO

TEXT

412a1–412b9

BOOK II, CHAPTER I

THE DEFINITION OF THE SOUL

Hitherto we have spoken of what our predecessors handed down to us about the soul. But let us now re-open the enquiry from the beginning and endeavour to determine what the soul is and what is its most comprehensive definition. § 211

Now, we say that one of the kinds of things that are is substance. Of this, there is one element, matter, which of itself is no particular thing; another, the form or species according to which it is called ‘this particular thing’; and a third, that which is from both of these. Matter is, indeed, potency, and the form, act; and this latter has two modes of being, one, like knowledge possessed, the other, like the act of knowing. §§ 212-16

Bodies especially seem to be substances; and, among these, natural bodies, for these are the principle’s of the others. Of natural bodies, some possess vitality, others do not. We mean by ‘possessing vitality’, that a thing can nourish itself and grow and decay. §§ 217-19

Therefore every natural body sharing in life will be a substance, and this substance will be in some way composite. Since, however, it is a body of such and such a nature, i.e. having vitality, the soul will not itself be the body. For the body is not one of the factors existing in the subject; rather, it is as the subject and the matter. It is necessary, then, that the soul be a substance in the sense of the specifying principle of a physical body potentially alive. Now, substance [in this sense] is act; it will therefore be the act of a body of this sort. §§ 220-6

Now this can mean one of two things: one, as is the possession of knowledge; another, as is the act of knowing. It is plain that it is like knowledge possessed. For the soul remains in the body whether one is asleep or awake. Being awake is comparable to the act of knowing, sleep to possession without use. Now knowledge possessed is prior in the order of generation, in one and the same thing. The soul, therefore, is the primary act of a physical body capable of life. §§ 227-9

Such a body will be organic. Parts of plants, indeed, are organs, though very elementary—the leaf is the covering of the pericarp and the pericarp of the fruit: roots, too, are like mouths, for both draw in nourishment. §§ 230-2

If then there is anyone generalisation to be made for any and every soul, the soul will be the primary act of a physical bodily organism. § 233

Hence it is unnecessary to enquire whether the soul and body be one, any more than whether the wax and an impression made in it are one; or in general, the matter of anything whatever, and that of which it is the matter. For while one and being are predicated in many ways, that which is properly so is actuality, § 234

ST. THOMAS’S COMMENTARY

LECTIO ONE

§ 211. Having reviewed, in Book One, other men’s opinions on the soul, Aristotle now begins Book Two of his Treatise, in which he sets out what he himself holds on the matter. First, then, linking up with what has gone before, he states his general aim; I and secondly, at ‘Now we say that one’, he starts to carry it out. He begins by saying that despite all the previous accounts of the soul it is necessary to go into the whole matter again from the beginning. The subject is so difficult that it is wiser to assume that the truth about it has not yet been discovered. And in answer to the question raised in the Introduction to Book One, whether one should first define the soul, and afterwards its parts, he decides now to define the essence of the soul before coming to conclusions about its parts. As though explaining this decision, he adds that we shall thus have acquired the most comprehensive idea of soul. For the definition of the soul itself comprises what is most common or general, whereas that of each of its parts or potencies comprises only some special aspect of it. And as he explains at the beginning of the Physics, the right way to teach is to begin with what is most general and end with precisions in detail.

§ 212. Beginning then at ‘Now we say’, his treatment divides into two parts, in the first of which he-shows what soul in general is, and in the second, starting at ‘Of the soul’s powers’, what are its parts or powers. The first part subdivides into (a) a definition that concludes, and (b) one that introduces, a demonstrative argument;—this latter part comes at ‘Since it is from the less clear’. Note in passing that any definition, as he says in Book I of the Posterior Analytics, is either the conclusion of a demonstration, e.g. ‘Thunder is a continuous noise in the clouds’, or it is the demonstration’s starting point, e.g. ‘Thunder is the extinction of fire in the clouds’, or it is the demonstration itself, but thrown into a different order, e.g. ‘Thunder is a continuous noise etc., caused by the extinction of fire etc.’ in which the conclusion and the starting point both appear, though not in syllogistic order.

As to (a), it includes first a definition of the soul, and then, at ‘It has been stated then’, an explanation of the definition. And to clear the ground before the defining proper begins (at ‘Therefore every natural body’), he makes some preliminary distinctions.

§ 213. It should be noted here that, according to the teaching of Book VII of the Metaphysics, there is this difference between defining substance and defining accidents that in the former case nothing extrinsic is included: every substance is defined in terms merely of its material and formal principles; but in the latter case something extrinsic to the thing defined is referred to, i.e. the subject of the accidents in question—as when one defines snubness as ‘curvature of the nose’. The reason is that a definition must express what a thing is, and while substance is something complete in its being and kind, accidents have being only in relation to a substance. In the same way no form as such is complete in kind; completeness in this sense belongs only to the substance composed of form and matter; so that the latter’s definition is complete without reference to anything else, whilst that of the form has to include d, reference to its proper subject which is matter. Hence, if the soul is a form its definition will not be complete without reference to its subject or matter.

§ 214. So, in the first part of this section, he makes certain distinctions, first in view of the work of defining the soul’s essence, and then, at ‘Bodies especially seem to be substances,’ in view of defining its subject. As regards the former point he alludes to three distinctions, of which the first is that of being into the ten categories; this he hints at when he says that substance is reckoned to be ‘one of the kinds of things that are’.

§ 215. The second distinction alluded to is that of substance into matter, form and the compound of both. Matter is that which is not as such a ‘particular thing’ but is in mere potency to become a ‘particular thing’. Form is that by which a ‘particular thing’ actually exists. And the compound is ‘the particular thing’ itself; for that is said to be a ‘particular thing’ (i.e. something you can point to) which is complete in being and in kind; and among material things only the compound is such. For although immaterial substances are not compounds of matter and form, still they are particular things, having actual existence in themselves, and being complete in their own nature. Not so the rational soul; for though it has the existence in itself which belongs to a ‘particular thing’, it is not a complete nature by itself; it is rather a part of a specific nature. Hence it is not in all respects a ‘particular thing’.

Matter, then, differs from form in this, that it is potential being; form is the ‘entelechy’ or actuality that renders matter actual; and the compound is the resulting actual being.

§ 216. Thirdly, he distinguishes two senses of the term ‘act’. In one sense knowledge is an act, in the other thinking is an act; and the difference can be understood by relating these acts to their

potencies. Before one acquires the grammatical habit and becomes a grammarian, whether self-taught or led by another, one is only potentially so; and this potency is actualised by the habit. But once the habit is acquired one is still in potency to the use of it, so long as one is not actually thinking about grammar; and this thinking is a further actualisation. In this sense, then, knowledge is one act and thinking another.

§ 217. Then at ‘Bodies especially’ he alludes to three distinctions which are presupposed by his enquiry into the meaning of the definition of the soul, so far as the subject endowed with soul is concerned. The first is the distinction between corporeal and incorporeal substances. Now the former are the most evident to us: for, whatever the latter may be in themselves, they do not impinge on our senses, but are only discoverable by an exercise of the reason. Hence he says that ‘bodies especially seem to be substances’.

§ 218. The next distinction, is between physical or natural bodies and artificial bodies. Man and wood and stone are natural bodies, but a house or a saw is artificial. And of these the natural bodies seem to be the more properly called substances, since artificial bodies are made out of them. Art works upon materials furnished by nature, giving these, moreover, a merely accidental form, such as a new shape and so forth; so that it is only in virtue of their matter, not their form, that artificial bodies are substances at all; they are substances because natural bodies are such. Natural bodies therefore are the more properly called substances, being such through their form as well as through their matter.

§ 219. Thirdly, he distinguishes between living and non-living natural bodies; and the living are those which of themselves take nutriment and grow and decay. Note here that this is said by way of example rather than definition. For, besides growth and decay, living things may exhibit sensation and intellectual knowledge and other vital activities. Immaterial substances, as is proved in the Metaphysics, Book XI, have the life of intellect and volition, though they cannot grow and do not take food. But because, in the sphere of things that are born and die, the plant-soul (the principle of nutrition and growth) marks the point where life begins, this soul is here taken as the type of all living things. However, life is essentially that by which anything has power to move itself, taking movement in its wide sense so as to include the ‘movement’ or activity of the intellect. For we call those things inanimate which are moved only from outside.

§ 220. After this, at ‘Therefore every natural body” he begins to define the soul, presupposing the distinctions already made. And his enquiry here has three parts: (a) he enquires into the elements of the definition taken separately; (b) at, ‘If, then, there is any one generalisation’, he states his definition; and (c) at ‘Hence it is unnecessary’, he uses it to refute an objection. As to (a) he first deals with the elements that refer to the soul’s essence, and then to those that refer to its subject, at ‘Such a body will be organic’, and in the part that concerns the essence he considers first the statement that the soul is an ‘act’, and then, at ‘Now this can mean one of two things’. that it is a ‘primary act’.

Aristotle’s first conclusion, then, in line with what has been said already, is that if physical bodies are substances in the fullest sense, all living bodies are substances too, for they are physical bodies. And as each living body is an actual being, it must be a compound substance. But just because to say ‘living body’ is to imply two things, the body itself and that modification of body by which it is alive, it cannot be said that the element in the composition referred to by the term body is itself the principle of life or the ‘soul’. By ‘soul’ we understand that by which a living thing is alive; it is understood, therefore, as existing in a subject, taking ‘subject’ in a broad sense to include not only those actual beings which are subjects of their accidental modifications, but also bare matter or potential being. On the other hand the body that receives life is more like a subject and a matter than a modification existing in a subject.

§ 221. Since, then, there are three sorts of substance: the compound; matter; and form; and since the soul is neither the compound-the living body itself; nor its matter—the body as the subject that receives life; we have no choice but to say that the soul is a substance in the manner of a form that determines or characterises a particular sort of body, i.e. a physical body potentially alive.

§ 222. Note that he does not say simply ‘alive’, but ‘potentially alive’. For by a body actually alive is understood a living compound; and no compound as such can enter into the definition of a form. On the other hand the matter of a living body stands to the body’s life as a potency to its act; and the soul is precisely the actuality whereby the body has life. It is as though we were to say that shape is an actuality; it is not exactly the actuality of an actually shaped body—i.e. the compound of body and shape—but rather of the body as able to receive a shape, of the body as in potency tq an actual shape.

§.223. But lest it be thought that soul is an actuality in the manner of any merely accidental form, he adds that it is a substantial actuality or form. And since every form has the matter proper to it, the soul must actualise just this special sort of body.

§ 224. The difference between accidental form and substantial form is that whereas the former does not make a thing simply be, but only makes it be in this or that mode—e.g. as quantified, or white— the substantial form gives it simple being. Hence the accidental form presupposes an already existing subject; but the substantial form presupposes only potentiality to existence, i.e. bare matter. That is why there cannot be more than one substantial form in any one thing; the first makes the thing an actual being; and if others are added, they confer only accidental modifications, since they presuppose the subject already in act of being.

§ 225. We can therefore reject the view of Avicebron (in the Book called Fons Vitae) that according to the way in which any given thing can be divided into genera and species so it can be divided into substantial forms. Thus an individual man would have one form that made him a substance, another that gave him a body, another that gave him life, and so on. But what our premisses compel us to say is that it is one and the same substantial form that makes a man a particular thing or substance, and a bodily thing, and a living thing, and so on. For the higher form can give to its matter all that a lower form gives, and more; the soul gives not only substance and body (as a stone’s form does) but life also. We must not think, therefore, of the soul and body as though the body had its own form making it a body, to which a soul is superadded, making it a living body; but rather that the body gets both its being and its life from the soul. This is not to deny, however, that bodily being as such is, in its imperfection, material with respect to life.

§ 226. Therefore, when life departs the body is not left specifically the same; the eyes and flesh of a dead man, as is shown in the Metaphysics, Book VII, are only improperly called eyes and flesh. When the soul leaves the body another substantial form takes its place; for a passing-away always involves a concomitant coming-to-be.

§ 227. Then, at ‘Now this can mean’, he examines the second term in the definition. He observes that there are two kinds of actuality, as we explained above, the kind that is like knowledge and the kind like thinking. And clearly the soul is of the former kind; for it is due to the soul that an animal is able to be both awake and asleep; and while waking is similar to thinking (for it is a use of the exterior senses just as thinking is a use of knowledge already possessed), sleep is more like the knowledge which lies dormant in the mind so long as it is not actually being used; for in sleep an animal’s faculties are quiescent.

§ 228. Now, of these two actualities, knowledge comes first in the order of coming-to-be in the same person; for it stands to thinking as potency to act. But in the order of nature or essence act is prior to potency (see the Metaphysics, Book IX) as the end and complete perfection of potency. And even in the temporal order of coming-to-be, act, in a quite general sense, is prior; for the potential is actualised only by something already in act. But in this or that particular thing considered in itself potentiality may come first; the thing may be actualised by degrees. Hence his remark that ‘knowledge... is prior (i.e. to thinking) in the order of generation in one and the same thing’.

§ 229. So he concludes that soul is the primary act of a physical body potentially alive, where act means the same sort of actuality as knowledge. He says primary act, not only to distinguish soul from its subsequent activities, but also to distinguish it from the forms of the elements; for these retain their own proper activities, unless impeded.

§ 230. Next, at ‘Such a body’ he examines that part of the definition which has to do with the soul’s subject, observing that the ‘physical body’ referred to is any organic body, i.e. any body equipped with the various organs required by a living body in consequence of the life-principle’s various vital activities. For from this principle (the soul) which is the richest of embodied forms, spring many different activities, so that it requires, in the matter informed by it, a full equipment of different organs. Not so the less perfect forms of inanimate things.

§ 231. Now plants, the least perfect of animate things, exhibit less organic diversity than animals. That is why Aristotle chooses plants to illustrate his assertion that every animate body is organic, saying that even plants have organically diversified parts. But these parts are very simple, i.e. like to one another; they lack the differentiation that we find in animals. Thus the foot of an animal is made up of different parts, flesh, nerves, bones and so forth, but the organs of plants are composed of less diverse sets of parts.

§ 232. The organic character of the parts of plants is displayed in their diverse functions. Thus a leaf functions as a covering for the pericarp, or fruit-bearing part, i.e. for the part in which the fruit is born. The pericarp, again, protects the fruit itself. So too the roots have a function in a plant similar to that of the mouth in an animal; they draw in nourishment.

§ 23 3. Next, at ‘if, then,’ he gathers all these observations into one definition, saying that if any definition covers all types of ‘soul’ it will be this: the soul is the primary actuality of a physical bodily organism. He does not need to add ‘having life potentially’; for this is implied in ‘organism’.

§ 234. Then at ‘Hence it is’ he applies this definition to solve a difficulty. There had been much uncertainty about the way the soul and body are conjoined. Some had supposed a sort of medium connecting the two together by a sort of bond. But the difficulty can be set aside now that it has been shown that the soul is the form of the body. As he says, there is no more reason to ask whether soul and body together make one thing than to ask the same about wax and the impression sealed on it, or about any other matter and its form. For, as is shown in the Metaphysics, Book VIII, form is directly related to matter as the actuality of matter; once matter actually is it is informed. Moreover, although, as he goes on to say, being and unity are variously predicated (in one way of potential, and in another way of actual, being), that is primarily and properly a being and a unity which has actuality. just as potential being is only a being under a certain aspect, so it is only a unity under a certain aspect; for unity follows being. Therefore, just as the body gets its being from the soul, as from its form, so too it makes a unity with this soul to which it is immediately related. If, on the other hand, we regard the soul in its function as the mover of the body, then there is no reason why it should not move by means of a medium, moving one part of the body by means of another.

TEXT

412b10–413a10

BOOK II, CHAPTER I, CONTINUED

THE DEFINITION EXPLAINED

SOUL AND BODY

It has been stated, then, what the soul in general is. It is ‘substance’ as definable form; and this means what is the essence of such a kind of body. If some utensil, for example an axe, were a natural body, then ‘being an-axe’ [axeishness] would be its substance, and this would be its soul. Apart from this, it would no longer be an axe, save equivocally. As it is, it is really an axe. And the soul is not the essence or ‘what-it-is’ of such a body as this, but of a natural body, such as has in itself the principle of motion and rest. §§235-8

Now what has been said should be considered with respect to parts. For if the eye were an animal, sight would be its soul. For this is the substance, in the sense of the definable form, of the eye. The eye is the matter of sight, and apart from this it is an eye no longer save equivocally, as with a painted or stone eye. What, therefore, holds of a part, we ought to apply to the whole living body: for the relation of a part [of the soul] to part [of the body] corresponds to that of sensitivity as a whole to the whole sensitive body, considered as such. §239

Not that which has cast off its soul is ‘capable of life’, but that which possesses it. But seed and fruit are only in potency such a body. As cutting or seeing is act, so is consciousness. The soul is like sight and the capacity of a tool; the body, like the thing in potency. But as an eye is a pupil together with the power of sight, so is there a living thing where there are both body and soul. §§ 240-1

Therefore it is evident enough that the soul is inseparable from the body—or certain parts of it, if it naturally has parts; for it is of certain bodily parts themselves that it is the act. But with respect to certain of its parts there is nothing to prevent its being separated, because these are acts of nothing bodily. Furthermore, it is not clear that the soul is not the ‘act’ of the body in the way that a sailor is of his ship. Let these remarks serve to describe and define the soul, in outline. §§ 242-4

ST. THOMAS’S COMMENTARY

LECTIO TWO

§ 235. The Philosopher now begins to explain the definition of the soul given in Lectio 1; after which, at ‘Therefore it is evident’, he draws a conclusion from it.The explanation has two parts, in the first of which he is concerned directly with the soul itself, while in the second, where he says ‘Not that which has cast off’ he explains that part of the definition which refers to the subject which has a soul. With regard to the soul itself, he begins by illustrating the definition by a comparison with artificial things; and then goes on, at ‘Now what has.’ to explain it by considering the parts of the soul separately.

In artificial things, made by human skiff, the forms imposed on the material are accidental forms; and since these are easier for us to perceive than is substantial form, as being more accessible to the senses, it is obviously reasonable to approach the soul, which is a substantial form, through a comparison with accidental forms. And again, the soul’s parts or potencies are more readily perceptible to us than its essence; for all our enquiry into the soul has to start from the objective terms of its activities and then proceed from these activities to their potencies, and thence to an understanding of the soul in its essence; that is why a study of the soul’s parts can throw light on the definition of it.

§ 236. First, then, he observes that the definition given above is ‘general’, i.e. it applies to any soul. It posits the soul as a substance, which is a form; and this means that it presents to us the idea of the essence of something. For there is this difference between a form that is substance and one that is not, that the latter sort are not strictly of the essence or ‘whatness’ of a thing: whiteness is not of the essence of a white body; whereas substantial form is essential and quidditative. To call the soul a substantial form, therefore, is to imply that it is of the essence and ‘whatness’ of the body it animates. Hence he says ‘this’, i.e. this quidditative substance, ‘is the essence of this body’, i.e. of the body that is what it is precisely through having this particular form. For this form is essential to the thing, and is denoted by the definition of what the thing is.

§ 237. And because substantial forms, including the forms of natural bodies, are not evident to us, Aristotle makes his meaning clear with an example taken from the forms (accidental) of artificial. things. ‘If’, he says, ‘some utensil (i.e. an artificial instrument) for example an axe, were a physical (i.e. a natural) body,’it would possess a form in the manner already explained. So he continues: ‘Then being-an-axe would be its substance,’ i.e. would be the substantial form of the axe, which is that to which we refer our idea of axe as such. This idea of axe as such he identifies with the essence of the axe, with what causes it to be an axe; and this essential form he identifies with the substance of the axe. He says ‘substance’ because the forms of natural bodies are substantial forms. Furthermore, if the axe were not merely a natural, but also an animate, body, its form would be a soul; and if it lost this soul it would no longer be an axe, except in name; just as when the soul leaves the body there is no longer an eye or flesh, except in name. Of course the axe, not being in fact a natural body, has no axe-form which is of the essence of the body that it is; so that if it lost the form of axe, the axe would still exist substantially, because the substance of artificial things is their matter which remains when the artificial form and, with this artificial form, the actuality of the artificial body as such, is removed.

§ 238. Then he explains why he has distinguished between the axe as it actually is and as it would be were it a physical (that is, a natural) living body: for the soul is not the essence and idea, i.e. the form, of an artificial body like an axe, but ‘of such a physical body’, i.e. of a body that is alive. To make this clearer he adds ‘as has in itself the principle of movement and rest’—which is characteristic of natural things. For Nature is this sort of principle, as he says in the Physics, Book II.

§ 239. Then at ‘Now what has been said’ he applies what has been concluded about the soul as a whole, and the animate body as a whole, to the parts of each. if, he says, the eye were a whole animal, its soul would be sight; for sight is the essential form of the eye; which in itself is the material condition of sight; in the same way as an organic body is the material condition of a soul. Once sight is lost, the eye, is no longer an eye, except in the sense that a stone or painted eye may be called an eye equivocally (this term is used when the same name is given to essentially different things). Remove, then, what makes an eye really an eye, and there is left only the name. And the same argument applies to the animate body as a whole: what makes it an animate body is its form, the soul. This removed, you have a living body only equivocally. For as one part of the sensitive soul is to one part of the sensitive body, so the faculty of sense as a whole is to the whole sensitive body as such.

§ 240. Next, at ‘Not that which has cast off’, he explains what was meant by defining the soul as the ‘act of a potentially animate body’. Now ‘potentially’ may be said about a thing in either of two senses: (a) as lacking the power to act; (b) as possessed of this power but not acting by it. And the body, whose act is the soul, is potentially animate in the second sense only. So, when he calls the body a thing potentially alive he does not mean that it has lost the soul it had and now lacks a life-principle altogether; he is speaking of what still has such a principle. On the other hand, seeds and the fruits that contain them are only potentially living bodies with souls; for a seed as yet lacks a soul. It is ‘potential’ therefore like that which has lost its soul.

§ 241. And to show just how the body is potential to the actuality that comes from its soul he adds that being awake is the actuality of the sensitive soul in the same way as cutting is the actuality of a knife and seeing is that of an eye; for each of these acts is the activity and use of a principle already there. But the soul is the first and underlying actuality; like the faculty of sight itself or the capacity of any tool; for each of these is the operative principle itself. So the body, complete with its soul, is potentially animate in the sense that, though it has its first actuality, it may lack the second. And as the eye is a thing composed of a pupil as its matter and the faculty of sight as its form, so an animal is a thing composed of soul as its form and body as its matter.

§ 242. Then, at ‘Therefore it is evident’, he deduces a truth from the foregoing. Having shown that the soul is the whole body’s actuality, its ‘parts’ being the actualities of the body’s parts, and granted that an actuality or form cannot be separated from that which is actual and has form, we can certainly conclude that no soul can be separated from its body,—at least certain parts of the soul ‘cannot be separated, if the soul can be said to have parts. For obviously some ‘parts’ of the soul are nothing but actualities of parts of the body; as we have seen in the case of sight, that it is the eye’s actuality. On the other hand, certain parts of the soul may well be separable from the body, since they are not the actuality of any corporeal part, as will be proved when we come to treat of the intellect.

§ 243. As to Plato’s opinion that the soul is the act of the body not as its form but as its mover, he adds that it is not yet clear whether the soul is the act of the body as a sailor of a ship, i.e. as its mover only.

§ 244. Finally, recapitulating, he says that the foregoing is an ‘outline’ description of the soul, meaning that it is extrinsic, as it were, and superficial and incomplete. It will be completed when he comes to define the innermost nature of the soul and the nature of each of its parts.

TEXT

413a11–413b13

BOOK II, CHAPTER II

THE DEFINITION JUSTIFIED

MODES OF LIFE

Since it is from the less clear, though more obvious, facts that what is certain and more evident to thought emerges, let us attempt to approach the matter afresh. § 245

For it is not enough that a defining principle should merely show a fact, as do most formulae, but also there should be contained and made plain the causes involved. Usually the constituent terms are like conclusions: for instance, what is a square that is equal to an oblong? An equilateral orthogon. Such a term is of the nature of a conclusion. But to say that a square is the discovery of a mean line states the reason why. §§ 246-52

Going back, then, to the beginning of our enquiry, let us say that the animate is distinguished from the inanimate by being alive.

To live, however, is predicated in several ways; and even if one only of these is present, we say there is life; as, for example, intellection, sensation, or movement and rest in place; as well as the movement and rest involved in nourishment, and growth and decay. §§ 253-5

Hence all plants seem to live. They appear to have in themselves a power and principle of this kind, by which they increase or decay in various directions—that is to say, they do not grow up but not down, but alike either way; and in all their parts they are continually nourished, and they live so long as they can take nourishment. §§ 256-7

It is possible for this power to exist apart from the others; but for the others to exist apart from it is impossible, at least in mortal beings. This is evident in plants; for there is in them no other soul-power. To live by this principle, then, is common to all living things. § 258

But an animal is such primarily by sensation. For we also call animals things that do not move or change their place, provided they have sensation, and do not merely live. There seem to be many of this sort: by nature they stay in one place, but they have one of the senses. § 259

Touch is in all, primarily. As the vegetative powers can be separated from touch and all sensation as a whole, so can touch from the other senses. (We give the name ‘vegetative’ to that part of the soul in which plants participate). All animals are seen to possess the sense of touch. § 260

For what cause each of these facts is so we shall say later on. At present only this need be said: that soul is the principle of the qualities we have discussed, and is characterised by the vegetative, sensitive, intellective and motive powers. § 261

ST. THOMAS’S COMMENTARY

LECTIO THREE

§ 245. Having defined the soul the Philosopher now sets out to prove his definition. First he says what he intends to do, and then, at ‘Going back, then,’ proceeds to do it. As to the former point, he first determines the method of demonstration that he intends to use; after which, at ‘For it is not enough’ he explains how certain types of definition can be proved. With regard to the method to be used we should note that, since we can only come to know the unknown if we start from what we know, and since the purpose of demonstration is precisely to cause knowledge, it follows that every demonstration must begin from something more knowable to us than the thing to be made known by it. Now in certain subjects, such as mathematics, which abstract from matter, what is the more knowable is such both in itself and relatively to us; hence in these subjects, demonstration can start from what is absolutely and of its nature more knowable, and therefore can deduce effects from their causes; whence the name given it of a priori demonstration. But in the quite different sphere of the natural sciences, what is more knowable is not the same thing in itself and relatively to us; for sensible effects are generally more evident than their causes. Hence in these sciences we generally have to begin from what is, indeed, absolutely speaking less knowable, but is more evident relatively to us (see the Physics, Book 1).

§ 246. And this is the kind of demonstration which will be used here. So he says that what is of its nature more certain, and is more evident to thought, becomes certain to us by means of things less certain in nature but more certain to us; and that this shows us the method to use in enquiring once more into the soul and showing the grounds of the definition given above.

§ 247. Then, at ‘For it is not enough’, he tells us why the question must be taken up again. Certain definitions can, he says, be demonstrated, and in these cases it is not enough for the defining formula to express, as most ‘formulae’, i.e. definitions, do, the mere fact; it should also give the cause of the fact; and this being given, one can then proceed to deduce the definition which states the mere fact. At present many definitions are given in the form of conclusions; and he gives an example from geometry.

§ 248. To understand which we must note that there are two kinds of four-sided figure: those whose angles are all right angles, and these are called rectangles; and the kind with no right angles, and these are called rhomboids. Of the rectangles, again, there is one with four equal sides—the square or tetragon; and another which, without having all four sides equal, has two pairs of equal and opposite sides—the oblong. Thus:

square oblong rhomboid

§ 249. Note further, that in any rectangular surface the two straight lines enclosing the right angle are said to contain the whole figure; because, the other two sides being equal to these two, each equal to its opposite, it follows that one of the enclosing lines measures the length of the whole figure, and the other its breadth: so that the whole figure is given in the contact of the two lines. If we imagine one of these lines moving along the other we see the whole figure form itself

§ 250. Note also that if, between the two unequal sides that contain the oblong, one takes the proportional mean and squares it, one gets a quadrilateral equal to the oblong. This would take too long to prove geometrically, so let a numerical argument do for the present. Let our oblong then have its longer side 9 feet and its shorter side 4 feet. Then the proportional mean line will be 6 feet; for as 6 is to 9, so 4 is to 6. Now the square of this line must equal the oblong; which is obvious numerically: 4 x 9 = 36, 6 x 6 = 36.

§ 2,51. Now it is thus, he says,’ that the question, What is a square (i.e. the quadrilateral equal to an oblong)? is answered; it is said ‘to be an orthogon’, i.e. a right-angled plane figure, which is ‘equilateral’, i.e. having all its sides equal, and so on. ‘Such a term’, i.e. a definition of this sort, is really ‘of the nature of a conclusion’, namely of a presupposed demonstration; whereas if one were to say that a square is ‘the discovery of a mean line’, i.e. of the proportional mean between the two unequal sides of the oblong, meaning that a square is what is constructed from this line, then at last the definition would disclose the ‘reason why’ of the thing defined.

§ 252. Note, however, that this example is only relevant to the definition of the soul in so far as this definition is simply to be demonstrated; it must not be taken to imply that our demonstration can proceed a priori from causes to effects.

§ 253. Next, at ‘Going back then’, he begins to prove the definition of the soul given above; and this in the way indicated, i.e. from effects to causes. This is how he sets about it: the first principle of fife in things is the actuality and form of living bodies; but soul is the first principle of life in living things; therefore it is actuality and form of living bodies. Now this argument is clearly a posteriori; for in reality the soul is the source of vital activities because it is the form of a living body, not e converso. So he has to do two things here; first, to show that soul is the source or principle of vitality, and secondly, to show that the first principle of vitality is the form of living bodies (this comes at ‘Since that whereby etc.’). With regard to the first point he does three things: (a) he distinguishes modes of life, (b) he shows that the soul is the principle of living activities—at ‘Hence all plants’; and (c) he explains how these parts of the soul are interrelated, by means of which it originates vital activities. This is at ‘We now ask whether each of these’.

§ 254. He starts then by saying that to carry put our intention of proving the definition of the soul, we must assume as a kind of principle that things with souls differ from those without souls in being alive. Life is the test; and as life shows itself in several ways, if a thing has life in only one of these ways it is still said to be alive and to possess a soul.

§ 255. Life, he says, shows itself in four modes: (1) as intellectual; (2) as sensitive; (3) as the cause of motion or rest in space; (4) as cause of the motions of taking nourishment, decay and growth. He distinguishes only these four modes, although he has already distinguished five main types of vital activity, and this because he is thinking here and now of the degrees of animate being. There are four such degrees, distinguished in the same way as the four modes in which life is manifested: for some living things, i.e. plants, only take nourishment and grow and decay; some have also sensation, but are always fixed to one place—such are the inferior animals like shell-fish; some again, i.e. the complete animals like oxen and horses, have, along with sensation, the power to move from place to place; and finally some, i.e. men, have, in addition, mind. The appetitive power, which makes a fifth type of vitality, does not, however, imply a distinct degree of living being; for it always accompanies sensation.

§ 256. Next, at ‘Hence all plants’, he shows that a soul is involved in all these modes of life. He does this with regard (1) to plants, and (2) to animals, at ‘But an animal is such, primarily’. Then (3), he summarises, at ‘For what cause”, what has been said and remains to be said. As to (1) he does two things. First he shows that the life-principle in plants is a soul. We have remarked, he says, that whatever evinces one of the four modes of life mentioned above can be said to live. Therefore plants are alive; for they all possess some intrinsic power or principle of growth and decay.

§ 257. Now this principle is not mere nature. Nature does not move in opposite directions, but growth and decay are in opposite directions; for all plants grow not only upwards or downwards, but in both directions. Hence a soul, not nature, is clearly at work in them. Nor do plants live only when actually growing or decaying, but, as things that take nourishment, they live so long as they can assimilate the food that induces growth.

§ 258. Next, at ‘It is possible’, he shows that this principle of feeding and growing can exist apart from other life-principles, but these cannot exist apart from it, at least in things subject to death. He adds this last clause because of immortal beings like immaterial substances or heavenly bodies; because, if these have a soul, it is intellectual; it is not a capacity to take nourishment. And the separability of this life principle from others is clearly evident in plants which have, in fact, no other one but this. it follows that what first of all causes life in mortal things is this principle of growth and nourishment, the so-called vegetative soul.

§ 259. Then, at ‘But an animal is such primarily’ he shows that a soul is the source of living in animals. And here he does two things. First he observes that what primarily distinguishes animals is sensation, though there are animals which have local movement as well; for we call those things animals (not just living beings) which have sensation, even if they are fixed to one place. For there are many such animals whose nature restricts them to one place, but which have the power of sense, e.g. shell-fish, which cannot move from place to place.

§ 260. Then at ‘Touch is’ he shows that touch is the primary sense in animals. For just as the vegetative soul, he says, is separable from all the senses including touch, so touch is separable from all the other senses. For many inferior animals have only the sense of touch; but there are no animals without this sense. Now that degree of soul in which even plants participate we call the vegetative. Hence we can distinguish three degrees of living beings: first, plants; secondly, the inferior animals fixed to one place and with no sense but touch; and, thirdly, the higher, complete animals which have the other senses and also the power to move from place to place. And a fourth degree consists, evidently, of beings which have all this and mind as well.

§ 261. Finally, at ‘For what cause’ summarising what has been said and remains to be said, he remarks that the cause of both these phenomena, namely the separability of the vegetative principle from sensation and of touch from the other senses, will be -given later on. He does this at the end of the whole Treatise. For the present it suffices to say that ‘soul’ is the one principle underlying the four distinct modes in which life is manifested, namely the vegetative mode which belongs to plants and to all living things; the sensitive mode in all animals; the intellectual mode in all men; and fourthly, the mode that is a power to move from place to place, which exists in all the higher animals, both those with senses only and those with intellect as well.

TEXT

413b13–44a28

BOOK II, CHAPTER II, CONTINUED

DIFFERENT KINDS OF SOUL

We now ask whether each of these [powers] is a soul, or a part of a soul: and if a part, whether it is separable only in thought or has also a distinct place. § 262

Concerning some of these powers it is not difficult to see [the answers to our questions]; others, however, give rise to doubts. For, as in the case of plants some, on being divided, seem to go on living in separation from one another, as if there were in each plant one soul in act, but several in potency; so we find it happens in the case of other differentiations of soul, for instance in divided animals each division has sensation and local motion; and if sensation, phantasm and appetition; for where there is sensation there is pleasure, and pain, and where these are there must necessarily be appetition. §§ 263-7

But as regards intellect and the speculative faculty, nothing has so far been demonstrated; but it would seem to be another kind of soul, and alone capable of being separated, as the eternal from the perishable. It is evident, however, from the foregoing, that the other parts of the soul are not separable, as some have said. § 268

By definition, however, they are obviously distinct. For if feeling is other than opining, the sense-faculty will differ from the capacity to form opinions. Likewise with each of the other powers mentioned. § 269

Further, all these powers are in some animals; in others, some only; in yet others, only one. This makes the varieties of animal. Why this should be so will be considered later. The same obtains with regard to the senses: certain species of animal have all; certain others, some; yet others have only the one most necessary, touch. § 270

Since ‘that whereby we live and perceive’ can mean two things,—like ‘that by which we know’. for we name one thing knowledge, and another, the soul, though we are said to know by both of these; and likewise as ‘that by which we are healthy’; for health is one thing, while a part of the body (or the whole of it) is another; and in these cases knowledge, or health, is the form and specific essence or ratio, and, as it were, the act of such as can receive knowledge in the one case and health in the other (for the action of an agent seems to exist in the recipient or disposed material)—and soul being that by which we primarily live and perceive and move and understand it follows that the soul will be a sort of species or ratio; not, as it were, a matter or substratum. Substance is predicated in three ways, as we have said: in one way as the form; in another as the matter; and in another as what is from both. Of these, matter is the potency, form the act; hence if what is from both is the animate being, the body is not the act of the soul, but the soul of the body. §§ 271-5.

And on this account they were right who thought that the soul is neither apart from the body nor the same as the body; for it is not, indeed, the body; yet is something of the body. And therefore it is in a body, and a body of a definite kind; and not as some earlier thinkers made out, who related it to a body without defining at all the nature and quality of that body; despite the fact that it is apparent that not any subject whatever can receive any form at random. And that such is the case is confirmed by reason: the act of any one thing is of that which is in potency to it, and it occurs naturally and fittingly in matter appropriate to it. That the soul, then, is an actuality and formal principle of a thing in potency to exist accordingly, is evident from these considerations. §§ 276-8

ST. THOMAS’S COMMENTARY

LECTIO FOUR

§ 262. After showing that ‘soul’ is the one principle common to the several types of vitality, the Philosopher now enquires into the various principles of the latter, asking how they are related both to the soul and to each other. And he does two things here. First, he put two questions (a) If the soul, the life-principle, is realised actually as a vegetative, sensitive, locomotive or intellectual principle, is each of these principles to be identified with the soul proper, or is each no more than apart of the soul? Now obviously, where the thing’s vitality consists entirely in growing and taking nourishment (as in plants) the vegetative principle is simply the soul or life-principle itself. But where the thing also has sensation, this vegetative principle is only a part of the soul. And the same reasoning applies to other cases. (b) If each of these principles is a part of the life-principle, as in the human soul which contains all of them, are they parts in the sense that they are merely diverse powers of the one soul, existing in one thing though they can be thought of apart from one another, or are they distinct beings having each its distinct locality, so that the sense-power is in one part of the body, appetition. in another, locomotion in another, and so on; as some indeed have thought.

§ 263. Secondly, when he says ‘Concerning some of these’, he answers the above questions: first the second one; then, at ‘Further, all these powers’, the first. The second question is answered in two parts: (a) with respect to the local separability of the parts of the soul, and (b) at ‘By definition’ concerning their separability in the mind. As to (a) he says that some parts of the soul raise no difficulties, but that others do.

§ 264. And he illustrates this by a comparison with plant-life. Certain parts, he says, of plants can be cut off and yet seem to go on living; for the cuttings, grafted or replanted, unite with a new stem or with the soil. In these cases the life-principle appears to be actually single but potentially many. The same sort of thing is observable in the forms of inanimate physical bodies; as each such body is actually one and potentially many, so in the lower animate bodies whose parts are still undifferentiated, the soul exists as one whole actually, but as many potentially. For inanimate bodies can be divided into parts which each retain the same specific nature (e.g. air, water, minerals) and this nature was also the nature of the whole body; and it is somewhat the same with plants, the lowest order of animate beings; they require very little differentiation in their parts, and the life-principle of the whole survives, as such, in some of the separated parts.

§ 265. So also with those animals which remain alive after being cut up. Each division still has a sensitive soul: it will shrink back if you prick it. And obviously it can move about. So the same part retains, evidently, the principle of sensation and local movement. And if sensation, then it must also have imagination which is simply a certain motion derived from actual sensation, as we shall see later. Again, it must also have appetition, since sensation necessarily involves satisfaction or dissatisfaction, i.e. pleasure or pain, because it involves a contact with the congenial or the uncongenial. And pleasure and pain involve desire and appetition. So the divided parts of such animals are able to desire.

§ 266. Now if each such divided part contains the vegetative, sensitive, appetitive and locomotive principles all together, it is clear that these principles are not to be located in any special parts of the animal’s body. Yet certain powers are obviously so located: seeing is only in the eye, hearing in the ear, smelling in the nostrils, taste on the tongue and palate. But the fundamental and most necessary sense of touch is found over the whole body.

§ 267. A doubt may occur about imagination; for some assign to it a special organ of the body. But note that imagination (as will be shown later) in the lower animals is indefinite; it is definite only in the higher animals. Hence if we assign a special organ to imagination, this is because the special completeness and definiteness of its activities call for a special organ of the body, just as seeing requires an eye. But as to some powers of the soul it is not difficult to decide whether they are located in distinct parts of the body.

§ 268. Then, at ‘But as regards intellect’, he points to one part of the soul over which doubts may arise. About the intellect, or whatever we call the percipient or speculative faculty, we are still, he says, uncertain. No proof has yet been given of its location in any special or particular organ of the body. Yet even at first sight it would seem to be of a different nature from the other parts of the soul, and to exist ‘in a different way; and that it alone is separarable from the rest of the soul (and may even exist apart from any organ of the body) as what is immortal from what is mortal. That the other parts of the soul are not locally separated is now clear.

§ 269. Then at ‘By definition” he shows that they are mentally separable from one another. For we distinguish potencies by their relation to acts; if the acts are specifically distinct, then so are the potencies. Hence he says here that the sensitive and opining, i.e. intellectual, principles are diverse; meaning that,, as sensing is other than forming opinions, the faculties implied have distinct definitions. And the same is true of the other principles already mentioned.

§ 270. Then, at ‘Further, all these powers’, he answers the first of the two questions proposed above, observing that animals differ in this, that in some are found all the four vital principles mentioned above, in others only some of them, and in some only one. And where one only of these principles is found it is the soul itself; but where several are found together each is a part of the soul and the soul itself is named after the principal part, whether sensitive or intellectual as the case may be (the reason why animals differ in this way will be shown later). And as with the powers of the soul, so with the particular senses; for some animals, (the higher) have all the senses; some (e.g. moles) have some, but not all; while some (die lowest animals) have only the most necessary one, touch.

This passage might also be understood as referring to the statement, made a few lines earlier, that the parts of the soul which coexist ‘in any one animal are not distinct beings nor in different places. For from this one might argue that they are not separable as between one animal and another; which error this passage removes.

§ 271. Next, at ‘Since etc.’, he concludes, from the fact, that the soul is the first principle of life, to the definition of it already given; first proving this definition, and then, at ‘And on this account’, drawing some further conclusions. The proof runs thus. Granted that there are two principles of our being and activity, one (the form) will be prior to the other (the matter). Now both body and soul are principles of life in us, but the soul comes first in this respect. The soul then is the form of the living body; which agrees with the definition already given: the soul is the primary actuality of a physical body capable of life. Clearly, the middle term of this argument is the definition of the soul as the primary principle of life.

§ 272. The argument itself he sets out in four parts. (1) Explaining the major, he observes that we can speak of the principle of life and sensation from two points of view, formally or materially, just as we speak of the act of knowing as proceeding either from knowledge itself or from the soul; or as we speak of becoming healthy either with respect to health itself, or with respect to some part of the body, or to the whole of it. In both these cases, one of the principles is formal and the other material. For knowledge and health are forms or actualities of certain subjects: knowledge is a form of the part of the soul that knows, health of the body capable of health. Thus he says ‘capable of knowing’ and ‘capable of health’ in order to indicate the, particular subject’s aptitude to its particular form. For the actuality of an active principle, such as the form transmitted to matter by an agent, always appears to exist in what receives it and is adapted to it, i.e. in the subject, whose nature it. is to receive from some one particular active principle, and which is adapted to attain the final term of the receiving-process, namely the form in question.

§ 273. (2) At ‘and soul being that by which’, he states the minor, saying that the soul is the primary principle of our life and feeling and movement and understanding—these being the four chief manifestations of vitality already mentioned (for by ‘life’ here is meant the vegetative principle which, as has been said, is common to all living things). Now though it is in the body that we enjoy health, health itself is that by which we are called healthy primarily. Only in so far as the body has health are we said to be healthy. So too our souls are not said to know except in so far as they have knowledge; thus knowledge itself is that by which, primarily, the soul is said to be in the state of knowing. And the same is true of our body and its life; we are not said to live by the body except in so far as the body has a soul. Therefore he calls the ‘soul’ here the first principle of life and feeling, etc.

§ 274. (3) He concludes at ‘it follows that the soul’, linking this phrase with the previous one, that the soul is a sort of nature or specific form; not the material for, or mere subject of, anything.

§ 275. (4) Then at ‘Substance is predicated’, I he shows how this conclusion follows from the premisses. For it might have seemed to follow that the body no less than the soul was a form, since we call the body also a principle of life. So, to clinch the argument, he adds that if, as we have said, the term ‘substance’ can refer to three things, to matter, to form, and to the complex of both (the matter being the potential element; the form the actuality; and the complex the thing that is alive in this way) the body is clearly not the soul’s actuality, but rather the soul is the body’s; for the body is potential with respect to the soul. And if the foregoing argument has led us to the alternative that the specifying principle is either the soul or the body, we can now conclude that it is the soul; for it is now dear that the body is not the form of the soul.

§ 276. Then at ‘And on this account’, he deduces from the foregoing: (a) that they were right who thought that the soul required the body and yet was essentially distinct from it. It is not the body, for it is not matter; but it is essentially involved with the body, because it is its actuality; whence too it follows, as he says here, that it exists in that body whose actuality it is.

§ 277. (b) Being then in the body, and in a special kind of body, namely physical and organic, it is not, however, in it as the old natural philosophers fancied when they spoke of it. For they did not specify the kind of body that it has. Yet it does in fact have only one kind of body. And this we should expect a priori, it being natural to any act to be realised in some definite and appropriate material. So also, then, with the soul.

§ 278. Summarising, he concludes that the soul is a certain actuality and formal principle of that which exists accordingly, namely as potentially animate.

TEXT

414a28–414b31

BOOK II, CHAPTER III

THE SOUL’S POWERS IN GENERAL

Of the soul s powers already spoken of all are present in some, certain only are present in others, and one only in yet others. By the powers of the soul we mean the vegetative, the sensitive, the appetitive, the locomotive and the intellectual. §§ 279-87

In plants there is only the vegetative; in other living things, this and the sensitive; but if the sensitive is present, so must the appetitive be. For appetition means desire, and anger and will. Now all animals have the sense of touch; and where sensation is found there is pleasure and pain, the pleasant and the repugnant. What has these has appetite, this being desire for a pleasurable object. §§ 288-9

Further; all have a sense of nutriment, inasmuch as touch is lis sense. For all living beings are nourished by things dry and wet or hot and cold; and the sense of touch is of these. But they are nourished by the other sense-objects only indirectly. Sound, colour and smell contribute nothing to nutrition; and as for savour, it is found in objects of touch. Hunger and thirst being appetites, hunger for the hot and dry and thirst for the cold and liquid, savour is as it were the delectable in these. We must settle these questions later; for the present let us only say that animals endowed with touch have appetition also. The case of imagination is not clear and must be examined later. Some animals, again, have local motion; some intellect and mind—such as men and whatever other beings there are of a like nature, or of one even more excellent. §§ 290-4

It is therefore clear that the idea of soul must be one in the same way as that of figure: for as there is no figure other than the triangle and those that derive from it, so there is no soul apart from the aforesaid. There will be, however, in the case of figures a general idea applicable to all figures, yet proper to none. Likewise with these souls just mentioned. Hence it is absurd to seek a common definition in this matter (or in any other) which will be that of no existing thing, and on the other hand, to seek to define in terms of the individual species without taking into account such a common definition. There is indeed an analogy between what holds of figures and what holds of the soul. For in that which is consequent there is always potential that which is primary, both in figures and in animate beings. As the triangle is contained in the square, so is the vegetative in the sensitive. §§ 295-8

ST. THOMAS’S COMMENTARY

LECTIO FIVE

§ 279. After defining the soul in general Aristotle comes to treat of its ‘parts’. Now the soul has no parts except in the sense that its potentialities are parts of it; in that one subject, being in potency to many activities, its power with respect to each in particular can be called a part of it. To treat of its parts then is to treat of its various potencies. This he does here in two main sections: the first treats of the soul’s powers in general and their distinction from one another; the second, at ‘Hence we must speak first’, takes them one by one. The former subdivides into (a) a division of the powers of the soul; and (b) at ‘So we must enquire” a discussion of what has to be proved about them, and how and in what order. The division itself of the powers (at ‘it is therefore clear’) necessitates showing how the soul as a whole is related to its parts; but before we come to this, the powers enumerated have to be related to each other, which he does at ‘In plants there is etc.’ First of all, then, he observes that, of the powers already enumerated, all are in some beings (men); some are in some beings (the other animals); and one only is in some others (plants). And having previously called them, not ‘powers’, but ‘parts’ of the soul, he clearly implies that the two terms mean the same. Now of these parts or powers there are five main types: the vegetative, sensitive, appetitive, locomotive and intellectual.

§ 280. Regarding this five-fold division two things must be made clear: (1) why the usual threefold division of potencies into vegetative, sensitive and intellectual is set aside; and (2) why he has already made a fourfold division.

§ 281. As to (1) we should note that all potencies are defined by their proper acts, and operative potencies by activities. The soul, being a form, has operative potencies; hence by differences between its activities we have to differentiate between its potencies. Now, as the activity of anything is consequent upon and corresponds to its being, we have to study vital activities precisely in the living beings which display them.

§ 282. The being of things whose actuality is ‘soul’, i.e. of the animate beings that exist on this earth and are the subject of the present discussion, this being includes two factors: one, material, in which it resembles the being of all other material things; and the other, immaterial, by which it has something in common with the world of the higher substances.

§ 283. Now there is this difference between these two divisions of being, that in so far as a thing is material, it is restricted by its matter to being this particular thing and nothing else, e.g. a stone; whilst in so far as it is unmaterial, a thing is free from the restriction of matter and has a certain width and infinity, so that it is not merely this particular subject but, in a certain sense, it is other things as well. That is why everything pre-exists, somehow, in the higher immaterial substances, as in universal causes.

§ 284. But in the lower terrestrial natures there are two degrees of immateriality. There is the perfect immateriality of intelligible being; for in the intellect things exist not only without matter, but even without their individuating material conditions, and also apart from any material organ. Then there is the half-way state of sensible being. For as things exist in sensation they are free indeed from matter, but are not without their individuating material conditions, nor apart from a bodily organ. For sensation is of objects in the particular, but intellection of objects universally. It is with reference to these two modes of existence that the philosopher will say, in Book III, that the soul is somehow all things.

§ 285. The activities, therefore, appropriate to living things in their material being are those we attribute to the vegetative soul. They fulfil the same purpose as the actions of inanimate beings, i.e. to attain and maintain existence; but they do this in a higher or nobler way. Inanimate bodies are brought into being and maintained by an exterior moving principle, whereas animate beings are generated by an intrinsic principle, i.e. seed, and are kept in existence by an intrinsic nutritive principle. It seems characteristic of living things that their activities should thus proceed from within themselves. But the purely immaterial activities of living things we identify with the intellectual part of the soul; while those in between belong to its sensitive part. Hence it is usual to distinguish three kinds of soul: vegetative, sensitive, intellectual.

§ 286. But since everything exists as formed in a certain way, the being of the sensible must have a sensible form, and the being of the intelligible an intelligible form. Now every form has by nature a certain trend or tendency whence proceed its activities or operations. Thus the form of fire tends naturally upwards (giving to fire its lightness) whence follows fire’s activity which is the movement upwards. Now the trend that proceeds from a sensible or intellectual form is called sensitive or intellectual desire; as that of any form in nature is called a natural desire. And from this desire follows the activity of local movement. Here then is the explanation we required of the five-fold division of the powers of soul.

§ 287. And as to the second point, note that when Aristotle wished to show that soul was the life-principle in things that five, he divided these into grades; which are not the same as those different kinds of vital activity whence we get our division of the powers of the soul. For, since all things that sense also desire, desire or appetition does not constitute a distinct grade of animate being; so we are left with only four such grades.

§ 288. Then, at ‘In plants there is only’, he shows the interconnection of the powers of the soul, thus explaining what he said previously, that all these powers are in some things, some of them in tome, and only one in some others. Here we have to consider that the completeness of the Universe requires that there should be no gaps in its order, that in Nature there should everywhere be a gradual development from the less to the more perfect. Hence, in the Metaphysics, BookVIII, Aristotle likens the nature of things to numbers; which increase by tiny degrees, one by one. Thus among living things there are some, i.e. plants, which have only the vegetative capacity,—which, indeed, they must have because no living being could maintain an existence in matter without the vegetative activities. Next are the animals, with sensitivity as well as vegetative life; and sensitivity implies a third power, appetition, which itself divides into three: into desire, in the stricter sense, which springs from the concupiscible appetite; anger, corresponding to the irascible appetite—both of these being in the sensitive part and following sense-knowledge; and finally will, which is the intellectual appetite and follows intellectual apprehension.

§ 289. That appetition exists in all animals he demonstrates in two ways. (1) All animals have at least one sense, touch; but where there is any sensation there is pleasure and pain, joy and sorrow. Now while joy and sorrow seem to spring from inward apprehension, pain and pleasure come from external sensations, especially from touch. But joy and sorrow necessarily imply some sweet or disagreeable object, i.e. something pleasant or painful. For everything touched is either congenial to the one touching, and then it gives pleasure; or uncongenial, and then it gives pain. But whatever can feel pleasure and pain can desire the pleasant. Since then all animals, without exception, have a sense of touch, all can desire.

§ 290. (2) This second argument begins at ‘Further, all have’ and runs thus. All animals have the sense that is aware of food; and this is touch; which is as necessary therefore to every animal as eating the food that agrees with it. The fact that it is touch that perceives food is clear if we consider that, as living bodies are made up of warm, moist, cold and dry elements it is of these that their food must consist; and these elements are just what touch is aware of. But other sense-objects’, he says, do not, save indirectly, nourish living bodies; they do so only so far as they are involved in the objects of touch. Sound, colour, smell have nothing to do with food as such; they occur in food only in so far as things that sound or are coloured or odorous, are also hot, or cold, moist or dry. Savour, however, is reckoned a tangible quality—so that tasting is a sort of touch. Clearly, then, all animals have a sense-awareness of food.

§ 291. But whatever has this awareness can feel the two desires of nourishment, hunger and thirst. Hunger is desire for the hot and the dry elements, i.e. food; thirst for the cold and the moist, i.e. drink. Savour is a certain delectability in food and drink indicating a proper balance of the hot and cold, the moist and dry elements. It is more of a pleasure added to eating than a necessity. Desire, then, always accompanies touch.

§ 292.What imagination has to do with desire and sensitivity will be shown later.

§ 293. Now besides these three powers, the vegetative, the sensitive and the appetitive, some animals also have the capacity to move from one place to another. Some, too, i.e. human beings and any other kind of beings, if such exist, resembling or even perhaps excelling mankind, have, in addition to these four capacities, the power of understanding or intellect. The beings ‘more excellent’ are the immaterial substances and the heavenly bodies, the latter, however, only if they are alive. Among living corruptible beings the human race alone is endowed with intellect.

§ 294. For as intellect has no bodily organ, intelligent beings cannot be differentiated according to a physical diversity in the constitution of their bodily organs, as are the different species of animals (whose different constitutions cause them to sense in different ways).

§ 295. Then at ‘It is therefore clear’ he shows how his definition of soul is related to the ‘parts’ that we have enumerated. To understand him here we must remember what Plato said about universal ideas, that they had a separate existence of their own. He did not say, however, that objects which follow successively from each other, such as numbers and geometrical figures, had a universal idea, i.e. he did not posit a universal idea of Number apart from particular numbers—as, for him, there was a universal idea of Man in addition to all existing men; and this because the classes of number are, of their nature, derived successively from each other, so that the first of these, duality, is the cause of all the rest. There is no need to posit a general idea of Number as the cause of the numerical species. The same argument applies to geometrical figures. They follow each other in the same way as numbers: from the triangle comes the tetragon, and from the latter the pentagon.

§ 296. Aristotle, then, says that the idea of Soul is one in the same way as that of geometrical figure is one. just as there is no figure existing apart from the triangle and the rest, as their common idea, so it is with the soul. There exists’ no soul apart from the parts which have been enumerated.

§ 297. But while, there is (even for the Platonists), no figure existing apart from all figures, nevertheless one common definition can be found which answers to all figures, without being proper to any particular one. And the same is true of living beings. It would be ludicrous therefore to seek a common definition, whether of animals or anything else, which did not fit any particular living thing actually existing. On the other hand it will not do to look for a definition that will fit only one sort of soul, ignoring what all have in common. We need a common definition which must, however, be applicable to souls in particular.

§ 298. He goes on now to show the resemblance between the two definitions, namely of soul and of geometrical figure. In both cases what comes first is potentially in what follows. In figures the three-sided figure exists potentially in the square; for the square is divisible into two triangles. Likewise the sensitive life-principle contains the vegetative, both as potential, as it were, with respect to sensitivity, and also as a certain life-principle in itself. The same holds good with the other figures and the other divisions of soul.

TEXT

414b32–415a22

BOOK II, CHAPTER III, CONTINUED

THE SOUL’S POWERS CONTINUED

THEIR INTERRELATION

HOW TO DEFINE EACH

So We must enquire in each particular case what the soul is of each: of plant, of man, of beast § 299

It must be considered why they stand in this order: for there is no sensitive soul without the vegetative, yet in plants the vegetative exists apart from the sensitive. Again, there can be no sense apart from that of touch, but touch exists without the others; for many animals have no sight or hearing or sense of smell. Again, among sentient beings, some. have local motion, others not. Last and least extensive of all [the species] that reasons and understands (as man and any other such). For mortal beings which possess reason have also all the other [powers], but reason is not found in all that have any one of the latter; some indeed have not even imagination, others live by this alone. The speculative intellect is another issue.

Clearly then, whatever is the most precise definition with respect to each of the above will be that also of the soul. §§ 300-2

CHAPTER IV

It is necessary lbr the student of these [parts of the soul] to discover what is the nature of each, and only then to investigate habits and other matters. § 303

But if one is to say what each of them is (namely the intellectual power or the sensitive or the vegetative) one must first say what it is to understand or perceive by sense; for actions and operations are prior to faculties in the order of thought. And if this is so, one ought first to consider the appropriate objects; which are prior even to the operations, and correspond to them;,and thus to determine, in the first place, what these objects are—for instance, food and the sense-object and the intelligible. §§ 304-8

ST. THOMAS’S COMMENTARY

LECTIO SIX

§ 299. After enumerating the powers of the soul and showing how the general definition given above is related to the particular divisions. of soul, the Philosopher now explains what remains to be cleared up and in what order. There are, he says, still two points to be made clear, one of which links up with the argument just given. For we have seen that, just as we must not be satisfied with a completely general definition of soul, such as will not express any of its particular realisations, so too we cannot rest content even with a definition which does answer in some way to these latter; we must pursue our enquiry until we shall have defined precisely what is proper to each of these divisions of soul in particular. Whence it follows that we have to ask about each particular type of living being—plant or man or animal—what is its own particular life-principle; thus applying and particularising our common notion of soul.

§ 300. Then at ‘It must be considered’, he states the next point to be decided. He has already said that the parts of the soul follow each other in a series like the kinds of geometrical figure; and it remains to consider the reason for this. This reason will be given at the end of the Treatise; here he only shows how the parts of soul follow one from the other successively. The sensitive part, he says, cannot exist without the vegetative, but the latter can, in plants, exist without the sensitive. And this is not surprising; for, as we have seen, the purpose of the vegetative activities is to attain and retain existence itself, which is the ground of all the rest, as it were. And the senses display a like sequence; there. are no senses at an unless there is touch; but touch itself can exist without the others. Many animals neither see, nor hear, nor smell, but only touch. And this will appear quite reasonable if we consider that by touch an animal is aware of the elements of which its substance consists (what it consists of and is nourished by), with which elements the other senses are only indirectly concerned. Hence the latter are not necessary for all animals, and in fact are found only in the higher animals.

§ 301. Again, there is the connection between sensitive and motive powers. Motive power cannot exist without sensitive, but the converse is not true. Some sentient beings move from place to place, but not all. We are speaking of the progressive movement of animals from one place to another; which is not found in all ,animals; though such as lack it show certain local movements of expansion and contraction—for instance, shellfish.

The ultimate division of soul—and the least extensive since it is not subdivided into different species—is that which has the power of reason and understanding; because where reason exists in mortal beings, there also are found all the other aforesaid powers. He says ‘mortal’ to exclude immaterial substances and the heavenly bodies (if these are alive) which, as neither being born nor dying, do not need the vegetative power; and as being able to understand by a direct intuition of the intelligible object, do not require sense-knowledge as a preliminary condition of understanding; whereas in corruptible natures all the sub-intellectual powers are presupposed as instruments preparing the way for intellect, which is the final perfection of Nature. But these sub-intellectual powers do not necessarily imply reason in the subjects that possess them. And in view of the affinity between intellect and imagination (as he said above, intellect either is, or is accompanied by, imagination), he adds that some animals lack not only intellect but also imagination.

§ 302. Now this might seem to contradict a previous remark of his, that if a part cut from an animal retains sensation and desire, it retains also images—if the latter imply imagination, as seems likely. We must therefore say that (as will be shown in Book III)3 the lower animals have indeed a sort of imagination but indeterminately: i.e. the activity of imagining does not, in them, outlast actual sense-apprehension, as it does in the higher animals which retain images of things sensed after these have been removed. Thus, as he says here, imagination varies in different animals. Some animals, lacking reason, live only by imagination, being led by it as we are led by reason. And though certain other animals lack both imagination and speculative intelligence, these two powers are not the same, as we shall see.

Clearly, then, the definition of the soul which has been given applies very precisely to each part of the soul.

§ 303. Then, at ‘It is necessary’, he shows the order to be followed in examining the parts of soul. From one point of view, he explains, the first thing to do is to define the nature of each of these parts; and then consider ‘habits’, i.e. whatever other parts of soul derive from them, and anything else pertaining to them and to whatever they animate, such as the organs of the body and things of that kind. This procedure is necessary to avoid confusion.

§ 304. Then, at ‘But if etc.’, he observes that, from another point of view, our definition of any part of the soul—intellect or sensitivity or vegetativity—must begin from the act of the part in question, e.g. understanding or actual sensation; because in idea acts and operations precede potentialities. Potentiality is nothing but a capacity to act or be acted upon; it essentially involves a relation to actuality and can only be defined in such terms. And if this is the case with acts and potencies, acts in their turn connote something prior to themselves, i.e. their objects.

§ 305. For the type of every act or operation is determined by an object. Every operation of the soul is the act of a potentiality—either active or passive. Now the objects of passive potentialities stand to these as the causal agents which bring each potentiality into its proper activity; and it is thus that visible objects, and indeed all sensible things, are related to sight and to the other senses. But the objects of the active capacities are related to these as the final terms attained by their activities; for in this case the object is what each of these activities effectively realises. It is obvious that whenever an activity effectively realises anything besides the activity itself, the thing thus realised is the final term of the activity (cf. the Ethics, Book I); for example a house is the final term of building. Hence all the objects of the soul’s activities are either causal agents or final terms; and in both respects they specify those activities.

For, obviously, specifically diverse causal agents do specifically diverse things—as heat heats and cold chills. And so also with the final term of activity: becoming well or becoming ill differ as ‘doings’, because health differs from illness. Thus in the work of seeking definitions we have to consider the objects of the soul’s operations before these operations themselves.

§ 306. We ought, therefore, to reach conclusions about objects before activities for the same reason as leads us to define activities before potencies. The ‘objects’ in question are such things as food and sensible being and intelligible being, with respect to the vegetative, sensitive and intellectual faculties respectively.

§ 307. But note that the activities and powers of soul are not distinguished with respect to distinct objects except precisely in so far as these are objects. For instance, visible being differs from audible being precisely as object. But if there is no difference as object, then it does not matter what other differences there may be; they win not essentially affect the kind of activity or potentiality. Thus by the same faculty we see a coloured man and a coloured stone; the difference is merely incidental to the object of the faculty.

§ 308. Note too that our intellectual potency is, as such, only potentially intelligible; in order to be understood it must be actualised through an idea drawn from sensible images. A thing is knowable only in the degree that it is actual; hence our intellectual potency attains to self-knowledge only through possessing an intelligible object in a concept (as will be explained in Book III), and not by directly intuiting its own essence. This is why the process of self-knowledge has to start from the exterior things whence the mind draws the intelligible concepts in which it perceives itself; so we proceed from objects to acts, from acts to faculties, and from faculties to essence. But if the soul could know its essence in itself and directly it would be better to follow the reverse procedure; for in that case the closer anything was to the soul’s essence, the more directly could it be known by the soul.

TEXT

415a23–415b28

BOOK II, CHAPTER, IV, CONTINUED

THE VEGETATIVE PRINCIPLE

HOW SOUL CAUSES BODY

We must first speak of nutrition and generation. For the vegetative soul is present in others, and is primary, and is that most general power of the soul by which life is present in anything: its operations being reproduction and the use of nutriment. §§ 309-10

For the most natural of the operations of such living beings as are mature, and not defective nor spontaneously generated, is to produce others like themselves: an animal an animal, and a plant a plant. To this extent do they participate, as far as they are able, in the imperishable and the divine. For this all things seek after, doing all that they do by nature for the sake of this. Now ‘that for the sake of which’ anything takes place, is twofold, one, the end ‘for which’, the other the end ‘in which’. Since then they cannot share by a continuous being, in the divine and everlasting (since nothing corruptible remains for ever numerically one and the same) each shares in this as far as it is able, one, however, more, and another less. And thus it endures, not the same, but as if the same; one indeed, but in species, not numerically. §§311-17

The soul is the cause and principle of the living body. Now these words can be used in many ways. The soul, however, is a cause in three established senses: for it is that whence comes movement; that ‘for the sake of which’; and as the essence of living bodies. § 318

That it is as the essence is evident. For in all things, the essence is the cause of existence. In things that live, to live is to be; and the cause and principle of this is the soul. § 319

Further: of that which is in potency, the act is the [immanent] idea. § 320

It is manifest that the soul is also a cause ‘for the sake of which’. For Nature operates for a purpose, in the same way as, as mind; and this is its end. Such is the soul in living thin according to Nature. For all natural bodies are instruments of the soul: whether of animals or of plants, they”exist as for the sake of the soul. ‘For the sake of’ is a phrase used in two ways, as ‘that for which’, and ‘that in which’. §§ 321-2

But also the soul is the principle whence comes local motion. Yet this power is not present in all living things. Change and growth are, however, due to a soul, while sensation seems to be a kind of alteration, and nothing senses unless it has a soul. The same holds good of growth and decay; for nothing undergoes growth or decay physically, unless it is nourished; and nothing is nourished which does not share in life. § 323

ST. THOMAS’S COMMENTARY

LECTIO SEVEN

§ 309. Having distinguished the capacities of ‘soul’ from one another, and explained how and in what order he means to discuss them, the Philosopher now treats of them in the order indicated. This he does in two stages. First, he examines one by one the divisions into which he has analysed soul, coming to certain conclusions about all of them. After that, in the penultimate chapter of this book, where he says, ‘All living things have the vegetative soul’, he explains the interrelation of these ‘parts’ of soul.

The former section divides into four treatises:

(1) On the vegetative principle.

(2) Starting at ‘These questions being settled’ [II, 10: §350] on the sensitive principle.

(3) At ‘As to the part of the soul by which it knows’ [III, 7: §671], on the intellect.

(4) At ‘We must now consider’ [III, 14: §795], on the principle of local movement.

To the appetitive principle is assigned no special treatise, because it does not of itself constitute any special grade of animate being. It is treated, along with motion, in Book III.

Treatise (1) divides into two parts: the first part contains certain preliminaries to the study of the vegetative principle; the second, beginning at ‘Since the vegetative and generative’ [II, 9: §333], contains Aristotle’s conclusions on this matter. The former section again divides into (a) a statement of his aim, and (b) at ‘For the most natural’ [§311] an exposition of certain things which an understanding of the vegetative principle presupposes.

§ 3 10. (a) First of all, then, he remarks that if, as we saw in the last chapter, objects and acts have to be defined before potencies, and the fundamental potency before those which follow from it, we ought in consequence to begin by discussing nourishment, the object with which the vegetative principle deals, and generation, which is this principle’s activity. Now this principle should be discussed first; because, whenever it coexists in one subject with the other parts. of ‘soul’, it is as it were their foundation; for through its activities the physical reality, underlying both sensitivity and intelligence, is maintained. Besides, this part of ‘soul’ is common to all living things, and while it can exist apart from the others, they cannot exist without it; and it is always best to start with the more general datum. Its activities, then, being reproduction and taking nourishment, it is with these that we begin.

§ 3 11. (b) Next, when he says ‘For the most natural’ he settles a few preliminary questions; and this in two stages. First, he shows that to generate one’s kind is an act of the vegetative principle. This he had not yet shown, having spoken so far only of growth and decay in this connection. Next, at ‘The soul is cause’, he proves that a soul is the principle of all vegetative activities (for indeed these activities might have seemed to come from mere nature, and not from a life-principle, since it is of their essence that they make use of the active and passive physical and corporeal qualities; and still more, because life in plants is hard to discern and latent).

§ 312. The first point is proved thus. All activities found to be natural to all living things spring, as we have seen, from the vegetative principle as the fundamental condition of there being any life at all; and reproduction being one such activity, it must spring from the vegetative principle. Indeed, he relates reproduction to this principle because it is, as he says, the activity most natural to all living things; and this because in a certain way the process of generation is common to all beings, even to inanimate things. Of course the latter are generated differently; still, they are generated. But with them the generating principle is something quite exterior to the thing that comes into being, whereas animate things proceed from an, interior principle inasmuch as they spring from the seed with its potentiality for new life.

§ 313. There are, however, three exceptions to the general rule that living things reproduce their kind. First, the immature; for children do not beget. Secondly, those defective in some essential requirement, such as the impotent and eunuchs. Thirdly, the case of spontaneous generation from putrefying matter. In this last case the life resulting is of a type so inferior that the general environment suffices to cause it, i.e. the influence of the heavenly bodies and the right material conditions. But these causes alone are not sufficient to generate the higher animals: this requires also the activity of particular causes of the same species as the animals generated.

§ 314. Hence he says that any living thing can reproduce its kind provided that it is ‘mature’ (excluding children) and not ‘defective’ (excluding eunuchs and such like) and that the effect generated is not ‘spontaneously generated’ (excluding things produced by putrefaction, which are said to come to be ‘spontaneously’ because they spring up without seed, which is something like the way things are done, as we say, spontaneously, i.e. not under exterior compulsion). And what he means by living things producing their like is that animals produce animals and plants plants; and more precisely that each species produces its like, men producing men and olive-trees olive-trees. And the reason why living things produce their like is that they may continuously participate, so far as they can, in what is divine and immortal, i.e. that they may become as like to the divine as possible.

§ 315. For just as there are degrees of perfection in one and the same being, inasmuch as it develops from potentiality into act, so there are more and less perfect beings; and therefore the more perfect a given thing is in itself, the more does it resemble the more perfect beings. Hence just as, while a thing is moving from potency to actuality, and as long as it is still in potency, it has a natural relation and inclination towards actuality, and when it attains incomplete actuality it still desires a more complete actuality, so, in the same way, everything in a lower form of existence is inclined to the maximum possible assimilation to the higher form. Hence Aristotle adds that ‘all things seek this’, i.e. an assimilation to what is divine and imperishable, and this is that ‘for the sake of which they do all that they do by nature’.

§ 316. Now ‘that for the sake of which’ something is done can mean two things: (a) the end aimed at directly by an activity, as health is the direct aim of doctoring; and (b) as the end aimed at indirectly; and this again may be taken in two ways. For we might take the ‘end’ to include also that subject in which the activity’s direct aim is realised, and in this sense the end of doctoring would be not health merely, but a healthy body. Alternately, we could mean by ‘end’ not only what is principally intended, but also the means to be employed; we might say, e.g. that the end of doctoring was to keep the body warm, because warmth preserves that harmony of elements in the body which is health. So then, when it is said here that perpetuity of being is the reason for the activity in question, we are referring either to some imperishable nature which material things strive, by reproducing their kind, to resemble, or to the reproductive process itself, which is the means to this end.

§ 317. Because, then, the lower forms of life are unable to share in the perpetual, divine being by way of continuity of their individual identity—since it is absolutely and intrinsically necessary (not merely a necessity imposed from without) that all corruptible things should individually pass away since they are intrinsically material—it follows that they can only share in it so far as their nature allows; the more lasting natures more, the less lasting less; but all sharing in it continuously by way of reproduction; each remaining one and the same, not indeed literally, but ‘as if the same’ in the sense that one and the same species remains. Hence he adds that it does not remain one thing numerically, i.e. in the strict sense of the terms, but only specifically; and this because each individual reproduces its like according to species.

§ 318. Then, at ‘The soul is the cause’, he shows the connection between the activities attributed to the vegetative principle and the soul. And he does two things here: first, he establishes a truth; secondly, at ‘Empedocles’, he points out an error. The proof of the truth, again, has two stages. First, he states his aim, asserting that the soul is principle and cause of the living body; and since these terms are ambiguous, going on to distinguish three senses in which this proposition is to be taken. Soul, he says, is cause of the living body, (a) as the source of its movements, (b) as ‘that for the sake of which’, or end, and (c) as its ‘essence’ or form.

§ 319. in the second place, at ‘That it is’, he proves his proposition; and first with regard to soul being the cause of the living body as its form. Here he uses two arguments: first, the cause of anything as its ‘essence’, i.e. form, is the same as the cause of its being, for everything has actual existence through its form. Now it is the soul that gives being to living things; for their being is precisely their life, which they have from the soul. Hence the soul causes the body as its form.

§ 320. Then the second argument, at ‘Further’: the actuality of anything is the immanent idea and form of the thing as in potency. Now the soul, as we have seen, is the living body’s actuality. Therefore it is the form and immanent idea of the living body.

§ 321. Next, at ‘It is manifest’, he shows that the soul is a final cause of living bodies. For Nature, like mind, acts for a purpose, as was shown in Book II of the Physics. But the mind, in its constructions, always orders and arranges materials in view of some form. So also, then, does Nature. If then the soul is the living body’s form, it must also be its final cause.

§ 322. Moreover the soul is the end not only of living bodies, but also of all sublunary natural bodies. For it is evident that all such bodies are, as it were, instruments of ‘soul’—not only of animals’ souls but of the plant soul as well. Thus men turn to their own, purposes both animals and inanimate things; animals make use of plants and inanimate things; and plants of the inanimate things which support and feed them. If then the action of things is an index to their nature it seems that all inanimate bodies are naturally instruments of animate things and exist for their sake. And, incidentally, the lower animate things exist for the higher. After this he distinguishes ‘for the sake of’ into the two aspects which have already been explained.

§ 323. Thirdly, at ‘But also the soul’, he shows that the soul is the source of movement in the body. The form of every natural body, he explains, is the principle of the characteristic movement of that particular kind of body—e.g. the form of fire is cause of fire’s movement. Now certain movements are characteristic of living bodies; such, for instance, as that by which animals move themselves about from place to place, though this, to be sure, is not found in all living things. Similarly sensation involves a certain alteration of the body not found except in beings that have soul. So too with growth and decay; these movements imply the use of food and therefore also a soul. The soul, then, is the principle of all these movements.

TEXT

415b28–416a18

BOOK II, CHAPTER IV, CONTINUED

THE VEGETATIVE PRINCIPLE CONTINUED

TWO ERRORS REFUTED

Empedocles is mistaken here, adding that growth occurs in plants by their sending a root downwards, because earth is by nature below, and also upwards because of fire. § 324

Nor did he understand aright ‘up’ and ‘down’; for these are not for all things the same as for the Universe; but roots of plants correspond to the head, in animals, if it is permissible to identify organs by their functions. For we reckon those organs to be the same which perform the same operations. §§ 325-7

Besides, what holds fire and earth together if they tend in contrary directions? They must come apart if there is nothing to prevent this. But if there is such a thing, it must be the soul; and be also the cause of growth and nourishment. § 328

Now it seems to some that the nature of fire is the sole cause of growth and nutrition; for it certainly seems to be the only one of the bodies and elements that is self-nourishing and self-increasing. Whence the notion that it is this that is operative in plants and animals. §§ 329-30

It is indeed a concomitant cause, but the cause absolutely is not fire, but rather the soul. For the increase of fire is infinite so long as there is anything combustible. But there are limitations to all things that subsist naturally, and some definite principle governs their dimensions and growth. And this belongs to the soul, not to fire, and to a specific principle rather than to matter. §§ 331-2

ST. THOMAS’S COMMENTARY

LECTIO EIGHT

§ 324. The Philosopher has just shown that the activities we call vegetative have their origin in the soul. He now proceeds to refute two errors on this subject, which he deals with respectively in two sections; the second of which begins at ‘Now it seems to some that the nature of fire’. In the first section he begins by stating the error, and then, at ‘Nor did he understand’ attacks it. Regarding the error itself, we should note that just as Empedocles refused to explain other cases of purposeful arrangement in Nature by any natural finality—for example he said that animals had the sort of feet they have, not in order to help them to walk, but simply because the matter of that part of their bodies happened to be arranged in that sort of way; so also the growth of living things he ascribed merely to the motion of light and heavy bodies. Observing that living things increase their size in different directions, e.g. up and down—as is evident in plants, which thrust their roots down and their branches up—he said that the downward growth of plants was due to the earth in their composition, which is heavy and therefore necessarily tends downwards; whilst their upward growth was due to fire which, being light, must tend upwards.

§ 325. Aristotle, then, at ‘Nor did he’, brings two arguments against this opinion of Empedocles. First, he says that Empedocles misunderstood ‘up and down’. To see what he means here we should note that ‘up and down’, and the other differences of position (before and behind, right and left) are differentiated in some objects naturally, whilst in others they are merely relative to ourselves. In things which have definite parts as the natural principle of their various movements, these positions are based on Nature itself Thus the Cosmos as a whole has a mid-point to which heavy things naturally tend, and a circumference to which light things naturally rise; which makes a natural cosmic difference between up and down, according to the natural resting places of the light and the heavy. Again, in living things and mortal beings up and down follow growth and decay: the upper is that part which takes in food, and the lower the opposite part which ejects superfluities.

§ 326. Again, in some animals before and behind are determined in relation to their senses, and the right and the left by their movements in space. But things, no part of which is a special source or term of movement, have no natural differences of position in themselves; these are fixed simply by the thing’s position relative to us. So is it with inanimate objects: the same pillar is said to be on the right or the left according as it is to the right or left of a man. Now in certain living things the natural upper and lower parts are fixed in the same way as in the Cosmos as a whole. It is so in man whose head is turned towards the top of the Cosmos and his feet to its bottom. But the reverse is found in plants, whose roots correspond to the head in man, since they function (as the part which takes in food) in the same way as the head in man. For we reckon that instruments are similar or dissimilar if their functions are so; hence the likeness between a plant’s roots and the head of an animal, although they point downwards. Up and down, then, mean opposite things in plants and in the Cosmos as a whole. But brute animals are different; their heads are turned neither up nor down in relation to the Cosmos as a whole. This is what he means when he says that up and down are not for all things (i.e. living things) what they are for the Cosmos.

§ 327. But Empedocles took up and down to be the same for all living things and for the Cosmos. And. indeed, if the movement of growth, by which we fix the upper and lower in living beings, followed the movements of the heavy and the light, by which the same relations are fixed for the Cosmos as a whole, then up and down would mean the same in all living beings and in the Cosmos. This is what led Empedocles to say that the roots of plants grew downwards.

§ 328. The second argument against Empedocles begins at ‘Besides, what holds’. To understand it, we should note that each element in a mixture is present not equally but virtually, and, therefore lacking the movement proper to itself. The whole mixture moves with the movement of the element that predominates. If each, as, Empedocles seems to have thought, retained its own movement, then, since the elements have natural movements in contrary directions, it follows that they would become quite separate from one another, unless some containing force held them together. Now it is just this container of the element which seems to be the chief cause of growth. For though, to be sure, the increase of the body in its various parts is due to diverse motions of the elements, yet,’ given the contrariety of elemental motion, growth is inconceivable unless the elements remain conjoined; otherwise there would be division, not growth. But in living things the soul is what holds the elements together; it is also, therefore, the’ source of their growth.

§ 329. Next, at ‘Now it seems to some’, he states another theory; which, at ‘It is indeed’ he then disproves. Unlike the theory. of Empedocles, which put the causes of growth and nutrition in both earth and fire, this theory ascribes them only to fire.

§ 330. The reason given is that the cause of anything’s modifications or motion would appear to be whatever had such modifications or motions essentially—e.g. fire, being essentially hot, is the cause of heat in things that contain other elements as well; and in the same way earth is the cause of heaviness. Now of the elements fire alone seems to ‘feed’ itself and to ‘grow’ ; if we take these terms in a superficial sense. Therefore fire alone would seem to cause growth and nutrition in plants and animals. But whether fire really feeds itself and grows will be made clear later.

§ 331. Then he attacks the above opinion. But note its grain of truth. All food has to be cooked, and this is done by fire, so that fire does play a part in nutrition, and consequently in growth also; not indeed as the principal agent (which is the soul) but as a secondary, instrumental agent. To say then that fire is a sort of concurrent or instrumental cause of growth and nutrition is true. But it cannot be the principal cause or agent, as he goes on to show.

§ 332. The principal agent in any action is that which imposes the term or natural limit upon what is done; thus in artificial things like boxes or houses the limit or term is fixed, not by the instruments used in the work, but by the art itself. The instruments, as such, are quite indifferent as to whether they are used to produce a thing of this shape and quantity or of that. A saw, as such, can be used to cut wood for a door or a bench or a house, and in any quantity you please; and if it cuts wood in this or that particular shape and quantity, this is due to the man who uses it. Now in Nature each thing obviously has certain limits to its size and its increase; each thing grows to a certain fixed pattern. For as each species of thing requires its own accidental modifications, so it needs its own measure of quantity, though some margin must be left to material differences and other individual factors. Men are nor all equal in size. But there is a limit both to their largeness and their littleness; and whatever determines this limit is the true principal cause of growth. But this cannot be fire, because the growth of fire has no naturally fixed limits; it would spread to infinity if an infinite amount of fuel were supplied to it. Clearly, then, fire is not the chief cause of growth and nutrition, but rather the soul. And this is reasonable enough, for the quantitative limits of material things are fixed by form—the specific principle—rather than matter. Now the soul of a living being is to the elements it contains as form is to matter; the soul, then, rather than fire, sets the term and natural limit to size and growth.

TEXT

416a19–416b31

BOOK II, CHAPTER IV, CONTINUED

THE VEGETATIVE PRINCIPLE CONTINUED

NUTRITION

Since the vegetative and generative faculties of the soul are a single power, it is first necessary to fix the nature of nutrition. For it is by this operation that [this power] is distinguished from the others. § 333

It would appear that food is a contrary to that which is fed: yet not every contrariety [involves feeding]; but only such contraries as find their increase as well as their origin in each other. For there are many things which originate from opposites: but not all derive their increase thus; (for instance, health coming from sickness). Nor, it seems, do all that do so nourish one another in the same way. For water is a food to fire, but fire does not feed water. And with uncompounded bodies this seems especially to be the case; that which feeds is one thing and that which is fed another. §§ 334-5

But a difficulty arises here. For some say that anything is nourished by what is similar to it; just as it is increased thus. But to others, as we have said, it seems, on the contrary, that a thing is nourished by its opposite,—as though it were impossible that like [should be altered] by, like; whilst food is altered and digested. Change in all things is either [to] an opposite or to a mean state. Moreover nutriment is acted upon by that which is nourished: not the latter by the nourishment; any more than a craftsman by his material; but this is acted on by him—the craftsman changing only from repose to activity.

It makes all the difference indeed whether food is. considered as what it is at first or as what it becomes finally. But if as both, in the one sense as undigested, in the other as digested, then certainly both the [above] theories of food can be upheld: for as it is undigested, one of two contraries is nourished by the other: but in so far as it is digested, one of two similars is nourished by the other. Whence it is clear that both parties speak in one way rightly, and in another way wrongly. § 339

Since only what is alive is nourished, what is nourished is the animate body as such. Wherefore nutriment means something related to what is animate, and this not incidentally only. §§ 340-2

To be nutritive and to be active are two distinct things. In so far as the living being is quantitative, food is active; but in so far as it is substantial, food is nutritive. It preserves the substance, and this just so long as it is fed. § 343

And it is productive of generation, not of the one nourished, but of such a one as the one nourished—for this latter is already a substance; and nothing generates itself, it only maintains itself in being. § 344

Wherefore, this soul-principle is a power able to preserve what possesses it as a thing of such a kind; and food is preparatory to the operation; hence the being cannot continue, deprived of food. § 345

Since there are three factors: what is nourished; that by which it is nourished; and that which nourishes; what nourishes is the primary soul, that which is nourished is the body containing it, and that by which it is nourished is food. § 346

Since all things are rightly named from their end and the end [of this soul] is to have generated another being like itself, then the primary soul is generative of what is like itself. § 347

‘That by which’ in nourishment is twofold, as ‘that by which’ in steering is the hand or the rudder: the one moving and moved, the other moving only. Now of necessity all food must be such that it can be digested, and what effects digestion is heat. Hence every animate being has heat.

In outline, then, we have stated what nutriment is: the subject must be further examined later in a special discussion. §§ 348-9

ST. THOMAS’S COMMENTARY

LECTIO NINE

§ 333. After showing that the activities called vegetative originate in the soul, the Philosopher proceeds to examine these activities. And first he examines their subject-matter, which is food. Next he shows how the activities and their subject-matter correspond—this at ‘Since only what is alive’. Thirdly, at ‘Wherefore this soul-principle’, he defines the faculties brought into play in these activities. As regards the first point he does three things: (a) he states the plan of the present argument; (b) at ‘It would appear that food’, he says what at first sight appears true about nutrition; to which (c) at ‘But a difficulty’ he brings an objection.

In the first place, then, (a) he observes that, as the vegetative and reproductive powers are included in the same general vegetative power (‘vegetative’ as a special power being really the nutritive power), we should discuss food first of all in relation to this power as a whole. For it is taking food that characterises this part of the soul as distinct from the intellectual or sensitive parts. For the other vegetative activities all presuppose taking food.

§ 334. Then (b) he states in three points what appears at first sight with regard to nourishment. First, food would always seem to be the contrary of the subject fed; and this because it has to become the latter, and becoming is from one thing to its contrary. Secondly, however, it seems to be clear that not any contraries will do; they must be such as can change into one another. Food is changed into the being of the one fed; hence all contraries which alternate in a subject without the one ever actually changing into the other have nothing to do with food. Thus sickness is not the food of health, nor white of black. But how substances come to contain contraries is another question.

§ 3 3 5. (c) Again, since increase of bulk seems to follow nutrition, the contraries involved must be such as affect each other in this way. Water may be generated by fire and e converso, but we do not say that water is fed by fire. Yet we can say that fire is fed by water, inasmuch as watery vapour nourishes fire. When water comes from fire there is no new coming-to-be of water; but fire can make use of and grow by means of watery vapours. Among the elements, therefore, only fire seems to be fed and only water seems to be food, taking water to include all vapours and liquids.

§ 336. Then at ‘But a difficulty” Aristotle brings an objection against what he has just said. The difficulty concerns the statement that food is a ‘contrary’. For some maintain that food should resemble the subject fed. Food causes growth, and a thing grows by what it resembles; otherwise the growth would be a mere addition of something extrinsic. Therefore like, it seems, is fed by like.

§ 337. To others, however, it seems that food must, as we have said, be contrary to what is fed. And they are moved by two reasons. (a) Food, being cooked, is transformed into the subject fed. But all transformation is either into a contrary or into an intermediate, as white into either black or grey. And the intermediate is a sort of contrary: grey compared with white, is black; and compared with black, is white; for it combines both. Therefore food is contrary to the subject into which it is transformed.

§ 338. (b) Again, every agent is contrary to that on which it acts; like is not passive to like. But food is passive to what is fed: it is transformed and digested. What is fed is not passive to its food, any more than an artist to his material (for it is the material that is altered, not the artist, except indirectly, in so far as he moves from potency to act). It would seem, then, that food is contrary to what is fed. Now the first of these two reasons is drawn from the contrariety between the two terns of a change; and the second from the contrariety between agent and patient. That which is fed, and itself acts upon the food, is the term into which the food is transformed.

§ 339. Then at ‘It makes all the difference’, he solves the problem, saying that the answer depends on whether by ‘food’ we mean what remains at the end of the process of heating and digesting, or what is received at first before this process begins. If food can be taken in both these senses—namely as the finished and as the raw product—then the two answers are both admissible. If it is taken in the latter sense, then subjects are fed by their contrary, which itself is acted upon and transformed; but if in the former sense, then like is fed by like; for the active agent assimilates what it acts upon, which is ultimately made like the agent and, as such, can increase the agent’s bulk. Thus both the above opinions were in one way true and another way false.

340. Next, at ‘Since only’, he shows how food is related to the activities of the vegetative principle: to taking nourishment; to growth (at ‘To be nutritive’) ; and to reproduction (at ‘And it is productive’).

First, then, he observes that nothing is fed except what has life and soul; hence the besouled body is what is fed. Now food is potential with respect to the subject fed; for it is changed into this subject. It follows that, inasmuch as food is the material of feeding, it is essentially, not accidentally, related to the besouled body as in potency to this body.

§ 341. Nothing then is, properly speaking, fed excepting what has a soul. Fire might seem to resemble in some way things that are fed, but it is not fed, strictly speaking. For that is properly said to be fed which absorbs something else in order to maintain its own being; and though this appears to happen with fire, it does not really happen. Once a fire has started, if you add fresh fuel, a new fire starts in the new fuel; but not in such a way that the new fuel maintains the fire already started before it was added. By starting a fire in fresh wood you do not maintain the flame in the other wood already burning. For the one flame made up of many flames is not one in the simple sense of the term; it is only one by the aggregation of many units, like a heap of stones. And it is this sort of unity that gives to burning a certain likeness to taking food.

§ 342. Living bodies, on the other hand, are really fed; food maintains life precisely where it already existed. This also is why only living bodies, properly speaking, grow; for each and every part in them is fed and increases; whereas inanimate things increase only by addition of part to part; what existed already does not increase, it is merely made into a new whole together with some other thing added to it.

But if fire has a special likeness to living and growing things, this is because the formal principle in fire is stronger than in the other elements, and its active power greater. It seems, therefore, to feed and grow because it so obviously seizes and subdues to itself other things.

§ 343. Then, at ‘To be nutritive’, he relates taking food to growth, observing that whilst the objective terms of feeding as feeding and of growing as growing are one and the same thing, they differ in idea. Food, we have seen, is in potency to the living body; which itself is both a quantum and a definite particular thing or substance. As a quantum it receives its food (which itself is a quantum) as a cause of growth; but as a particular sort of substance it receives food precisely as food. For it is of the nature of food to maintain the substance of what is fed; which is required by the continuous using up of natural warmth and moisture. Hence the substance of the thing fed lasts just so long as it is fed.

§ 344. Then at ‘And it is productive’ he relates nutrition to generation, as the latter’s cause. For seed, the generative principle, is the residue of food. And food is an agent in generating, not the subject fed, but other subjects of the same kind; for the subject fed already exists and cannot be generated afresh. Nothing generates itself; only what does not yet exist is generated. This is not to say, however, that things cannot maintain themselves.

§ 345. Next, at ‘Wherefore, this soul-principle’ he concludes with a definition of the powers of the vegetative soul: first, of the nutritive power, and then, at ‘Since all things’, of the whole vegetative principle. As to the nutritive power, he observes that it is simply that faculty by which a living being is able to maintain itself as such; while food is the condition of this faculty’s activity, that by means of which it maintains its subject. Hence loss of being follows lack of food.

§ 346. And, having remarked ‘that the source of nutritive activity is a capacity in the soul relating essentially to food, he goes on, at ‘Since there are three’, to show how that power and the food itself differ as sources of nutrition. Nutrition, he says, involves three factors: what is fed; that, wherewith it is fed; and the primary agent in feeding: this primary agent is the primary, i.e. vegetative, soul. What is fed is its body; and that wherewith it is fed is food. Thus a capacity in the soul is the cause of taking food as the principal agent; but food as the instrumental agent.

§ 347. Next, at ‘Since all things’, he defines that primary or vegetative soul (the entire soul of plants, but only part of any animal’s soul). To understand his definition, we must realise that the three vegetative activities fall into a certain order. First is taking food, by which things are maintained in being; the second and more perfect activity is growth, by which a thing increases in both quantity and capacity; while the third and most perfect and ultimate vegetative activity is reproduction, by which a being, already pretty complete in itself, gives existence and perfection to another being. For each thing is at its best, as is said in the Meteorologica, Book IV, when it can reproduce its likeness in another. If then all things are rightly defined and named in terms of their end, and the end of all the activities of the vegetative soul is to generate its likeness in another, it follows that we can suitably define this ‘primary soul’ as that which is reproductive of another, like to itself in kind.

§ 348. And in view of his previous remark that this primary soul’s instrument was food, to prevent anyone thinking that it had no other instrument, he shows, at ‘That by which’ that the subject fed has another instrument wherewith it is fed; just as in steering a ship there are two instruments. For the pilot steers with both hand and rudder. Now the hand is a conjoined instrument which has the soul for its form. Whilst, then, the rudder is an instrument which moves the boat and itself is moved by the hand, the hand itself is not moved by an exterior motive force, but by an interior one; for it is a part of the man and the man moves himself. Similarly, the instrument of nutrition is twofold. There is the separated instrument not yet informed by the soul; and this is food. But there must also be a conjoined instrument; for the food must be digested; and this requires heat. As then a pilot moves the rudder with his hand, and the boat with the rudder, so the soul moves the food with heat and, by means of the food, nourishes itself. The heat is the soul’s conjoined instrument; a natural warmth inseparably rooted in the soul and necessary to all living things as the condition of their digesting their food. And it. is because this primary soul is, unlike the intellect, the actuality of a. part of the body that it has a conjoined instrument.

§ 349. Summarising, Aristotle says that he has defined ‘in outline’, that is in general, what food is; later he will treat of it with more precision and finality. For he wrote a special book on food, as also on the generation and movement of animals.

TEXT

416b32–417a21

BOOK II, CHAPTER V

SENSITIVITY POTENCY AND ACT IN SENSATION

These questions being settled, let us speak of sensation in general. As has been said, sensation occurs in a being moved and acted upon; for it appears to be a kind of alteration. Some say, ‘like is acted on by like’. How far this is possible or impossible has been stated in our general discussion of activity and passivity. §§ 350-1

It may be asked why there is no sensation of the senses themselves; and why they do not produce sensation without something extraneous, seeing that they contain within themselves fire and earth and the other elements that give rise to sensation, either of themselves or through their accidental qualities. It becomes evident that the sensitive power is not an actuality, but is only potential; which explains why it does not sense [without an exterior object] as the combustible does not bum of itself without something to make it burn. Otherwise it would burn itself, and not need a fire already alight. § 352-4

But as we speak of sensing in two ways, (for we say that one who sees and hears in potency sees and hears, even when he happens to be asleep; and also that one does so actually) so we may speak of ‘sense’ in two ways,—as in potency and as in act. Likewise, to perceive is both potential and actual. § 355

To start with then, let us speak as if being acted upon and moved were the same as action and moving. For movement is a kind of activity, though imperfect, as has been stated elsewhere. § 356

All things are moved and affected by an agent, or something in act. Hence it is, that a thing is affected both by its similar and also by its dissimilar, as we have said. What is being affected is dissimilar: what has been affected is similar. § 357

ST. THOMAS’S COMMENTARY

LECTIO TEN

§ 350. After treating of the vegetative part of soul the Philosopher now begins to examine the sensitive part. This treatment divides into two sections, the first of which deals with what is most apparent in sensitivity, i.e. the exterior senses, while the second, beginning at ‘That there is no other sense’, treats of what is latent therein. In the former section Aristotle first explains how sense-faculties are related to sensible objects, and then, at ‘In treating of each sense’ he defines both faculty and object. Regarding the former point, he first repeats some earlier observations and then, at ‘It may be asked’, proceeds to the present problem.

First of all, then, he remarks that this is the place to start discussing the sensitive soul, beginning with a general view of the subject and going on later to a more detailed treatment. And he repeats two things already said: that to sense is to be moved or acted upon in some way, for the act of sensation involves a certain alteration of the subject; and secondly, that it was the view of some enquirers that the passivity of sensation was an instance of like being acted upon by like.

§ 351. For some early thinkers held that like is known and sensed by like: as Empedocles said, earth knows earth, fire knows fire, and so on. Now the general problem of the action of like upon like is discussed in the De Generatione, where Aristotle’s conclusion is that, although at the start of any action the agent and patient are contrary, when the action is finished they are similar. For the agent, in acting, assimilates the patient.

§ 352. Then, at ‘It may be asked’, he proceeds to the present problem. He shows that in themselves the senses are in potency; then, at ‘But since we speak of sensing in two ways’, that they are sometimes in act; and thirdly, at ‘Distinctions however’, he shows how they move from potency into act.

To understand the first of these three points, note that all who, like Empedocles, said that like was known by like, thought that the senses were actually the sense-objects themselves,—that the sensitive soul was able to know all sense-objects because it consisted somehow of those objects; that is, of the elements of which the latter are composed.

§ 353. Two things follow from this hypothesis. (1) If the senses actually are, or are made up of, the sense-objects, then, if the latter can be sensed, the senses themselves can be sensed. (2) Since the presence of its object suffices, to enable the sense-faculty to sense, then, if this object actually exists in the faculty as part of its composition, it follows that sensation can take place in the absence of external objects. But both these consequences are false. He introduces them here as specimens of the problems which the early philosophers could not solve. So he says, ‘It may be asked why there is no sensation of the senses’, i.e. why the senses themselves are not sensed; for it seems they would be sensed if they, the faculties, were really like their objects.

§ 354. It is also hard to see ‘why they do not produce sensation’, i.e. why actual sensation does not occur, ‘without something extraneous’, i.e. without exterior sense-objects; since, in the opinion of the ancients, fire, earth and the other elements belong to the inner nature of the sense-faculty and are perceptible by sense, either in themselves, i.e. in their essence (as these philosophers thought, not distinguishing between the senses and the intellect which alone perceives essence), or in the accidental qualities proper to them, namely heat and cold and so forth, which are essentially sense-perceptible. Now since these difficulties are insurmountable if the sense-faculty consists of its objects in their actuality (as the early philosophers thought), Aristotle concludes that the sensitive soul is clearly not actually, but only potentially, the sense-object. That is why sensation will not occur without an exterior sense-object, just as combustible material does not burn of itself, but needs to be set on fire by an exterior agent; whereas if it were actually fire it would burn simply by itself.

§ 355. Then, at ‘But as we speak of sensing’, he shows, by the two ways in which we speak of anyone sensing, that sensation is intermittently actual. For we sometimes say that a man sees or hears when he only does these things potentially, as when he is asleep; but sometimes we mean that what he is actually doing is seeing or hearing. Clearly, then, sensation and sensing may be referred to either in act or in potency.

§ 356. Next, at ‘To start with then,’ he explains the above. For to speak of sensation as ‘in act’ might seem contradictory to his previous statement that it was a certain passive being acted upon or moved; for to be in act seems to pertain to an active agent. So he explains that in calling sensation an ‘act’ he is referring precisely to the state of being acted upon or moved; inasmuch as this is a certain state of being actual. For movement has a certain actuality; which is the actuality (as he says in the Physics, Book III) of the imperfect or potential, that is to say, of changeable being. In the same way, being moved and sensation itself are a sort of action, as implying an actuality of being. The phrase ‘To start with’, however, means that he will add something later to show how the senses become actual in fact.

§ 357. Thirdly, at ‘All things are moved and affected’, he shows how it follows from the above that the old theory that like senses like cannot be true. Everything potential, he says, is acted upon and moved by some active agent already existing; which in its actualising function makes the potential thing like itself In some sense, then, a thing is acted upon by both its like and its unlike (as we have already remarked). At first, and while the transforming process is going on, there is dissimilarity; but at the end, when the thing is transformed and changed, there is similarity. And so it is as between the sense-faculty and its object. And the early philosophers went wrong because they missed this distinction.

TEXT

417a 22–417b17

BOOK II, CHAPTER V, CONTINUED

SENSITIVITY

POTENCY AND ACT CONTINUED

Distinctions however must be made concerning potency and act; for at present we are speaking of these in one sense only. § 358

For there is such a thing as ‘a knower’, in one sense, as when we say that man is ‘a knower’ because man is of the class of beings able to have knowledge. But also as when we speak of a, man as ‘knowing’ because he possesses the science of grammar. These two are not capable in the same way; but the former’s power is, as it were, generic and comparable to matter; whereas the latter has the power to consider at will, so long as no extraneous obstacle intervenes. Yet again, only he who is actually attending to (say) the letter A, is in the strictest sense knowing. §§ 359-61

Therefore the first two are knowing in potency. But one has undergone a change through being taught, and is often altered from the contrary state, whereas the other is moved to action from simply having sense or grammar without acting [accordingly]; but in a different way from formerly when he had not yet acquired any habit [of knowing]. §§ 362-4

Nor is ‘being acted on’ a simple term. It is one thing to be somehow destroyed by a contrary; quite another when what is in potency is maintained by what is in act, and is of a similar nature, being related to the latter as potency to act. §§ 365-6

For when a man possessed of knowledge becomes actually thinking, there is certainly either no ‘alteration’—there being a new perfection in him, and an increase of actuality;—or it is some novel kind of alteration. Hence it is as misleading a statement to say that a man is ‘altered’ when he thinks, as to say this of the builder when he builds. The process from being in potency to understand and think to actually doing so should not be called instruction, but has by rights some other name. §§ 367-8

The change from being in potency, in one who learns and receives instruction from another (who actually has learning and teaches) either should not be called a ‘being acted upon’ (as we have said), or there are two modes of alteration, one a change to a condition of privation, the other to possession and maturity. §§ 369-72

ST. THOMAS’S COMMENTARY

LECTIO ELEVEN

§ 358. Having explained how the sensitive faculties are both in act and in potency, the Philosopher now goes on to say how they are brought from potency into act. This he does in two parts: first distinguishing between act and potency, and between the diverse ways in which a thing may pass from one state to the other, taking his example from the intellect; and secondly, at ‘The first change in the sensitive being’, he applies all this to the case of sensation.

As regards the first of these parts he does three things: (a) he states his intention; (b) he distinguishes, at ‘For there is such a thing as’, between act and potency in the intellect; and (c) he explains, at ‘Therefore the first two’ how what is potential, in both the two senses of the term which have been distinguished, becomes actual.

First of all, then, he says he is about to discuss potency and act, in order to show the diverse ways in which things can be said to be actual or potential—because so far the two terms have been used ‘in one sense only’, i.e. without distinctions.

§ 359. Then at ‘For there is such a thing as’, he distinguishes act and potency in the intellect. We speak, he says, in one sense of potency when we say that man is a knower, referring to his natural capacity for knowledge. Man, we say, is one of that class of beings that know or have knowledge, meaning that his nature can know and form habits of knowing. In another sense, however, we say of someone that he knows, meaning that he knows certain definite things; thus we say of one who has the habit of some science—e.g. Grammar—that he is now one who knows.

§ 360. Now, obviously, in both cases the man’s capacities are implied by calling him a knower; but not in the same way in both cases. In the first case man is said to be ‘able’ through belonging to a certain genus or ‘matter’, i.e. his nature has a certain capacity that puts him in this genus, and he is in potency to knowledge as matter to its form. But the second man, with his acquired habit of knowing, is called ‘able’ because when he wishes he can reflect on his knowledge—unless, of course, he is accidentally prevented, e.g. by exterior preoccupations or by some bodily indisposition.

§ 361. A third case would be that of a man who ‘was actually thinking about something here and now. He it is who most properly and perfectly is a knower in any field; e.g. knowing the letter A, which belongs to the above-mentioned science of Grammar. Of the three, then, the third is simply in act; the first is simply in potency; while the second is in act as compared with the first and in potency as compared with the third. Clearly, then, potentiality is taken in two senses (the first and second man); and actuality also in two senses (the second and third man).

§ 362. Then where he says ‘Therefore the first two’, he explains (1) how both these types of potency are actualised, and (2), at ‘Nor is being acted on’, he discusses whether this actualisation is the result of a being acted upon.

First, then, he remarks that while in the two first cases there is potential knowledge, and while potency as such is able to be actualised, there is a difference, in respect of actualisation, between a primary and a secondary potency. One in primary potency to knowledge is brought into act through being, as it were, changed or altered by teaching received from another (the teacher) who already knows actually. And often, he says, this change is from a contrary habit; alluding to those who come to actual knowledge from a state of ignorance.

§ 363. Ignorance has two meanings. it can be purely negative: when the ignorant person neither knows the truth nor is involved in the opposite error; and in this case he is simply brought into actual knowledge, not changed by being rid of a contrary habit. On the other hand, ignorance may imply the bad condition of being involved in error contrary to the truth; and to acquire knowledge, then, one must be changed by being delivered from that contrary habit.

§ 364. But one in potency in the secondary sense—i.e. as already possessing the habit—passes from the state of having, indeed, sensations or knowledge but not exercising them, into the state of actually knowing something here and now. And this kind of actualisation differs from the other.

§ 365. Then at ‘Nor is being acted on’ he discusses the question whether both kinds of actualisation can be called being acted upon. First, he explains the different meanings of ‘being acted on’. Then at ‘For when a man possessed of etc.’, he applies these distinctions to the present problem. First, then, he remarks that being acted upon has several meanings, like potency and act. In one sense it implies some kind of destruction caused by a contrary quality. For in the strict sense the state of being passive to action seems to connote, on the side of the patient, a loss of something proper to it through its being overcome by the agent; and this loss is a sort of destruction, either absolutely, as when the patient loses its substantial form, or relatively, as in the loss of an accidental form. And the loss implies a contrariety in the agent, the imposition upon the patient’s matter, or being, of a contrary form from outside. In the first and strict sense, then, ‘being acted on’ means a destruction caused by a contrary agent.

§ 366. In another and looser sense the term connotes any reception of something from outside. And as a receiver is to what it receives as a potency to its actuality; and as actuality is the perfection of what is potential; so being acted upon in this sense implies rather that a certain preservation and perfection of a thing in potency is received from a thing in act. For only the actual can perfect the potential; and actuality is not, as such, contrary to potency; indeed the two are really similar, for potency is nothing but, a certain relationship to act. And without this likeness there would be no necessary correspondence between this act and this potency. Hence potency in this sense is not actualised from contrary to contrary, but rather from like to like, in the sense that the potency resembles its act.

§ 367. Next at ‘When a man possessed of’, Aristotle discusses whether the actualising of already acquired knowledge involves a being acted upon. And he takes first the transit from secondary potentiality into fullest actuality; and then at ‘The change from being in potency’, that from primary potentiality into the acquired habit of knowledge. Now, as to the former point, he asserts that this movement into actual thinking is not truly a passive being altered; for, as we have seen, no movement into act, as movement into act, is such. The term applies, strictly, only to the alteration of a subject from one to the other of two mutually exclusive qualities. But this is not what happens when a man begins to exercise his mind on knowledge he already possesses; rather, he is developing a quality already possessed; as Aristotle says here, it is ‘a new perfection in him and an increase of actuality’; for perfection increases with actuality. And if one insists on using the terms ‘actuality’ and ‘being acted upon’, they must be taken in a wider and less strict sense. And to illustrate the point he adds that it is just as inept to speak of a thinker being ‘altered’ when he actually thinks as to say of a builder that he is altered by building.

§ 368. A further conclusion: if it be granted that to pass from habitual to actual knowing is not a reception of new knowledge, but rather a drawing out and perfection of knowledge possessed already, it remains true that to be taught is to acquire new knowledge. Therefore, when a man is brought simply to the act of knowing or understanding, this ought not, strictly speaking, to be called ‘instruction’; it might be given some other name, though perhaps no other has in fact been found for it.

§ 369. Then at ‘The change from being in potency’, he discusses whether the transit from potency to act of one who acquires completely fresh knowledge is an ‘alteration’, in the sense of a ‘being acted upon’. He says that when a learner, previously knowing only potentially, is instructed by a master already knowing actually, one should either call this simply not a case of alteration and being acted upon, or else distinguish two kinds of alteration. The one kind is ‘a change to a condition of privation’, i.e. into qualities opposed to those which the thing already has, and incompatible with these, and therefore until now excluded by them. The other kind is ‘by a change to a possession and maturity’, i.e. through receiving habits and forms which perfect the thing’s nature and involve no loss of what it already has. And the learner is altered in this second sense, not in the first.

§ 370. Now this seems to contradict what was said above, that learners often changed from a contrary habit, and thus, it would seem, acquired qualities opposed to their former ones. But really, when one is brought from error to the knowledge of truth there is indeed a certain likeness to the change from one quality to its opposite, but it is only a likeness. For where there is true alteration both the opposed qualities—the terms of the process—are necessarily and essentially involved, e.g. becoming white involves not only white, but also black, or some intermediary colour which in relation to white is a sort of blackness. But where knowledge is acquired it is quite accidental that the learner was previously in error. He could learn without first being in error. Hence it is not in the true sense an alteration.,

§ 371. Another difficulty occurs where he says that the learner as such is taught by a master who already knows. For it does not always happen thus; a man may acquire knowledge by finding out for himself. To this we reply that whenever a potential knower becomes an actual knower, he must indeed be actualised by what is already in act. But this may be effected either by a purely extrinsic cause, as when air is lit up by an already actual fight, or by an intrinsic cause as well, as when a man is healed both by nature and by a doctor. In this latter case both causes of healing are actual health; for obviously health exists both in the mind of a doctor and in some healthy part of the man’s nature (i.e. the heart) in virtue of which the rest of the man recovers health. Doctors make use of such natural means to health as warmth or cold or other variable dispositions, so that we can say that the whole of their skill consists in helping nature to drive out sickness. If nature were strong enough she could do this by herself without a doctor’s aid.

§ 372. And the case is the same when a man acquires knowledge. For here again there are two principles involved: an intrinsic one, which a man uses when he finds things out for himself; and an extrinsic one, as when he learns from others. But in both cases a potency is actualised by something already in act. The fight of the agent intellect gives a man immediate actual knowledge of the first principles which we know by nature, and in virtue of this actual knowing he is led to actual knowledge of conclusions previously known by him only potentially. In like manner too a teacher can help him towards knowledge, leading him step by step from principles he already knows to conclusions hitherto unknown to him. Nor would this external aid be necessary if the human mind were always strong enough to deduce conclusions from the principles it possesses by nature; and indeed the power so to deduce is present in men, but in varying degrees.

TEXT

417b18–418a25

BOOK II, CHAPTER V, CONTINUED

SENSITIVITY

ACTUALISATIONS OF SENSE AND INTELLECT COMPARED

The first change in the sensitive being is caused by the parent. When it is born it is already endowed as with knowledge. Actual sensation corresponds to the act of thinking. §§ 373-4

 They differ, however. For the actuation of sense-operations is from without; namely from the visible, the audible, and so on for the other senses. The cause [of the difference] is that sensation, even in act, is of particulars: whereas scientific knowledge is of universals. For the latter are, in a way, within the soul itself; hence the act of the intellect is interior and at will; whereas sensation is not from within the soul, and requires that a sense-object be presented. The same holds good of the sciences which concern sense-objects, and for the same reason, i.e. that sense objects are singulars and are external. But there will be time later to deal with these more conclusively. §§ 375-80

For the present it is sufficiently established that ‘in potency’ is not univocally predicated; but it means one thing when, for example, we say that a child is able to be a soldier, and quite another thing when we say this of an adult. The same holds of the sensitive power. Since, however, this distinction has no name, and yet it is settled that the [two stages] differ, and in what way, it is necessary to use the expressions ‘to be acted upon’ and ‘to be altered’ as if they were precise terms. The sensitive power is potentially that which the sense-object is actually, as we have said. It is acted upon in so far as it is not like: it becomes like, in being acted upon; and is then such as is the other. §§ 381-2

ST. THOMAS’S COMMENTARY

LECTIO TWELVE

§ 373. After distinguishing between potency and act, and elucidating in terms of intellectual activity the transit from one state to the other, the Philosopher now applies what he has said to the case of sensation. First, he shows how there is a transit from potency to act in sensing. Secondly, at ‘They differ, however’ he explains the difference between the two cases. Thirdly, at ‘For the present it is sufficiently established’, he recapitulates what has been said about sensation.

Regarding the first point, we must take into account that, as in intellectual cognition, so too in sensation, potency and act are each two-fold. For what so far possesses no sense-faculty but is due by nature to have one, is in potency to sensation; and what has the sense-faculty, but does not yet sense, is in potency to actual sensation in the same way as we have seen in the case of acquired intellectual knowledge. Now, as a subject moves from primary potency into primary actuality when it acquires knowledge through teaching, so too a subject’s primary potency to the possession of a sense-faculty is actualised by his birth. But whereas a sense-faculty is natural to every animal,—so that in the act of being generated it acquires a sense-faculty along with its own specific nature—the case is not the same with intellectual knowledge; this is not naturally inborn in man; it has to be acquired through application and discipline.

§ 374. This is what he means by saying that ‘the first change in the sensitive being’ is caused by the parent. This ‘first change’, he explains, is from sheer potency to the primary actuality; and it is due to the parent; because there is a power in the semen to actualise the sensitive soul with all its capacities. Once an animal has been generated it has its senses in the same way as a man who has been taught possesses knowledge. And when it actually senses it corresponds to the man who actually exercises his knowledge by thinking.

§ 375. Then at ‘They differ, however’, he sets himself to discriminate between actual sensation and thinking; and he finds the first reason for distinguishing these activities in the difference between their objects, i.e. the sense-objects and intelligible objects which are attained by actual sensation and actual thinking respectively. The sense-objects which actuate sensitive activities—the visible, the audible, etc.—exist outside the soul; the reason being that actual sensation attains to the individual things which exist externally; whereas rational knowledge is of universals which exist somehow within the soul. Whence it is clear that the man who already has scientific knowledge about certain things does not need to seek such things outside himself, he already possesses them inwardly, and is able, unless prevented by some incidental cause, to reflect on them whenever he pleases. But a man cannot sense whatever he pleases; not possessing sense-objects inwardly, he is forced to receive them from outside.

§ 376. And as with sense-activities, so with the sciences of sense-objects; for the latter are individual things existing outside the soul. Therefore a man cannot speculate scientifically on any sense-objects, but only on such as he perceives in sensation. But there will be time to treat conclusively of this matter later on, in Book III, where we discuss the intellect and its relation to the senses.

§ 377. Concerning what is said here, we have to ask ourselves (a) why sensation is of individual things, whereas science is of universals; and (b) how exactly universals exist in the soul.

As to (a) we should note that while the sense-faculty is always the function of a bodily organ, intellect is an immaterial power—it is not the actuality of any bodily organ. Now everything received is received in the mode of the recipient. If then all knowledge implies that the thing known is somehow present in the knower (present by its similitude), the knower’s actuality as such being the actuality of the thing known, it follows that the sense-faculty receives a similitude of the thing sensed in a bodily and material way, whilst the intellect receives a similitude of the thing

understood in an incorporeal and immaterial way. Now in material and corporeal beings the common nature derives its individuation from matter existing within specified dimensions, whereas the universal comes into being by abstraction from such matter and all the individuating material conditions. Clearly, then, a thing’s similitude as received in sensation represents the thing as an individual; as received, however, by the intellect it represents the thing in terms of a universal nature. That is why individuals are known by the senses, and universals (of which are the sciences) by the intellect.

§ 378. As to (b), note that the term ‘universal’ can be taken in two senses. It can refer to the nature itself, common to several things , in so far as this common nature is regarded in relation to those several things; or it can refer to the nature taken simply in itself Similarly, in a ‘white thing’ we can consider either the thing that happens to be white or the thing precisely as white. Now a nature—say, human nature,—which can bethought of universally, has two modes of existence: one, material, in the matter supplied by nature; the other, immaterial, in the intellect. As in the material mode of existence it cannot be represented in a universal notion, for in that mode it is individuated by its matter; this notion only applies to it, therefore, as abstracted from individuating matter. But it cannot, as so abstracted, have a real existence, as the Platonists thought; man in reality only exists (as is proved in the Metaphysics, Book VII) in this flesh and these bones. Therefore it is only in the intellect that human nature has any being apart from the principles which individuate it.

§ 379. Nevertheless, there is no deception when the mind apprehends a common nature apart from its individuating principles; for in this apprehension the mind does not judge that the nature exists apart; it merely apprehends this nature without apprehending the individuating principles; and in this there is no falsehood. The alternative would indeed be false—as though I were so to discriminate whiteness from a white man as to understand him not to be white. This would be false; but not if I discriminate the two in such wise as to think of the man without giving a thought to his whiteness. For the truth of our conceptions does not require that, merely apprehending anything, we apprehend everything in it. Hence the mind abstracts, without any falsehood, a genus from a species when it understands the generic nature without considering the differences; or it may abstract the species from individuals when it understands the specific nature, without considering the individuating principles.

§ 380. It is dear, then, that universality can be predicated of a common nature only in so far as it exists in the mind: for a unity to be predicable of many things it must first be conceived apart from the principles by which it is divided into many things. Universals as such exist only in the soul; but the natures themselves, which are conceivable universally, exist in things. That is why the common names that denote these natures are predicated of individuals; but not the names that denote abstract ideas. Socrates is a ‘man’, not a ‘species’—although ‘man’ is a ‘species’.

§ 381. Finally, at ‘For the present etc.’, he recapitulates his remarks on sensation and observes that only now has it become clear that what we call potency has more than one meaning. It is in one sense that we say that a boy can be a soldier, i.e. by a remote potentiality. But in another sense we say that a grown man can be a soldier, i.e. by proximate potentiality. And the same distinction applies to sense-perception; as we have seen there are two ways of being in potency to sense anything. Though we have found no terms to express this difference, we have seen, nevertheless, that the two kinds of potency differ, and how they differ.

§ 382. And in spite of the fact that a thing which passes from the second stage of potency into act, through actualising its sense-faculty, ought not, strictly speaking, to be said to be ‘altered’ or ‘acted upon’, we cannot help using these terms; and this because the sense-faculty is potentially such as the sense-object is actually. It follows that, whilst at the start of the process of being acted upon the faculty is not like its object, at the term of the process it has this likeness. It was because they failed to make this distinction that the earlier philosophers thought that sense-faculties were composed of the same elements as their objects.

TEXT

418a6–418a26

BOOK II, CHAPTER VI

SENSE OBJECTS IN GENERAL

In treating of each sense we must first discuss sense-objects. We speak of a sense-object in three ways: two [kinds of sense-objects] are perceptible essentially; one incidentally. Of the two former, one is proper to each sense, the other common to all. § 383

Now, I call that the proper object of each sense which does not fall within the ambit of another sense, and about which there can be no mistake,—as sight is of colour, and hearing of sound, and taste of savour; while touch has several different objects. Each particular sense can discern these proper objects without deception; thus sight errs not as to colour, nor hearing as to sound; I though it might err about what is coloured, or where it is, or about what is giving forth a sound. This, then, is what is meant by the proper objects of particular senses. §§ 384-5

 Now the sense-objects in common are movement, rest, number, shape, dimension. Qualities of this kind are proper to no one sense, but are common to all; thus a movement is perceptible both by touch and by sight. These, then, are the essential objects of sensation. § 386

To be a sense-object ‘incidentally’ is said, for example, of a white object that is the son of Diares. This is perceived incidentally because whiteness happens to belong to what is perceived: but the sense, is unaffected by that object as such. Of objects essentially sense-perceptible, the proper are properly such; and to these the essence of each sense is naturally adapted. §§ 387-98

ST. THOMAS’S COMMENTARY

LECTIO THIRTEEN

§ 383. Having explained in general terms how sense-faculties are related to their objects, the Philosopher now begins his examination of objects and faculties separately. This enquiry divides into two parts, of which one is concerned with the sense-objects, and the other, starting at ‘It must be taken as a general rule’, with the faculties. The first part again divides into (a) a discrimination of the proper or special sense-objects from the rest, and (b) at ‘That of which there is sight’, an examination of the special objects of each sense. As to (a) he first makes a division of the sense-objects, and then, at ‘Now I call that the proper object,’ explains this division piecemeal.

Beginning then, he observes that before we decide what the senses themselves are we must discuss the objects of each sense; for objects are prior to faculties. Now the term sense-object is used in three ways, in one way incidentally, and in two ways essentially or absolutely; and of the latter we use one in referring to the special objects proper to each sense, and the other in referring to objects that-are common to more than one sense in all sentient beings.

§ 384. Then at ‘Now I call that’, he explains the members of the division, and first what he means by a special sense-object. He says that he means by this term what is perceived by one sense and by no other, and in respect of which the perceiving sense cannot err; thus it is proper to sight to know colour, to hearing to know sound, to taste to know flavour or savour. Touch, however, has several objects proper to itself— heat and moisture, cold and dryness, the heavy and the light, etc. Each sense judges the objects proper to itself and is not mistaken about these, e.g. sight with regard to such and such a colour or hearing with regard to sound.

§ 385. But the senses can be deceived both about objects only incidentally sensible and about objects common to several senses., Thus sight would prove fallible were one to attempt to judge by sight what a coloured thing was or where it was; and hearing likewise if one tried to determine by hearing alone what was causing a sound. Such then are the special objects of each sense.

§ 386. Next, at ‘Now the sense-objects’, he says, touching the second member of the division, that the common sense-objects are five: movement, rest, number, shape and size. These are not proper to any one sense but are common to all; which we must not take to mean that all these are common to all the senses, but that some of them, i.e. number, movement and rest, are common to all. But touch and sight perceive all five.

It is clear now what are the sense-objects that are such in themselves or absolutely.

§ 387. Then, at ‘To be a sense-object incidentally’, he takes the third member of the division. We might, he says, call Diarus or Socrates incidentally a sense-object because each happens to be white: that is sensed incidentally which happens to belong to what is sensed absolutely. It is accidental to the white thing, which is sensed absolutely, that it should be Diarus; hence Diarus is a sense-object incidentally. He does not, as such, act upon the sense at all.

While it is true, however, that both common and special sense-objects are all absolutely or of themselves perceptible by sense, yet, strictly speaking, only the special sense-objects are directly perceived, for the very essence and definition of each sense consists in its being naturally fitted to be affected by some such special object proper to itself The nature of each faculty consists in its relation to its proper object.

§ 388. A difficulty arises here about the distinction between common and incidental sense-objects. For if the latter are only perceived in so far as the special objects are perceived, the same is true of the common sense-objects: the eye would never perceive size or shape if it did not perceive colour. It would seem then that the common objects themselves are incidental objects.

§ 389. Now there are some who base the distinction between common and incidental sense-objects upon two reasons. They say that (a) the common objects are proper to the ‘common sense’, as the special objects are to the particular senses; and (b) that the proper objects are inseparable from the common objects, but not from the incidental objects.

§ 390. But both answers are inept. The first is based on the fallacy that these common sense-objects are the special object of the ‘common sense’. As we shall see later, the common sense is the faculty whereat the modifications affecting all the particular senses terminate; hence it cannot have as its special object anything, that is not an object of a particular sense. In fact, it is concerned with those modifications of the particular senses by their objects which these senses themselves cannot perceive; it is aware of these modifications themselves, and of the differences between the objects of each particular sense. It is by the common sense that we are aware of our own life, and that we can distinguish between the objects of different senses, e.g. the white and the sweet.

§ 391. Moreover, even granted that the common sense-objects were proper to the common sense, this would not prevent their being the incidental objects of the particular senses. For we are still studying the sense-objects in relation to the particular senses; the common sense has not yet been elucidated. As we shall see later, the special object of an interior faculty may happen to be only incidentally sensible. Nor is this strange; for even as regards the exterior senses, what is in itself and essentially perceptible by one of these exterior senses is incidentally perceptible by another; as sweetness is incidentally visible.

§ 392. The second reason is also inept. Whether or no the subject of a sensible quality pertains essentially to that quality makes no difference to the question whether the quality itself is an incidental sense-object. No one, for instance, would maintain that fire, which is the essential and proper subject of heat, was directly and in itself an object of touch.

§ 393. So we must look for another answer. We have seen that sensation is a being acted upon and altered in some way. Whatever, then, affects the faculty in, and so makes a difference to, its own proper reaction and modification has an intrinsic relation to that faculty and can be called a sense-object in itself or absolutely. But whatever makes no difference to the immediate modification of the faculty we call an incidental sense-object. Hence, the Philosopher says explicitly that the senses are not affected at all by the incidental object as such.

§ 394. Now an object may affect the faculty’s immediate reaction in two ways. One way is with respect to the kind of agent causing this reaction; and in this way the immediate objects of sensation differentiate sense-experience, inasmuch as one such object is colour, another is sound, another white, another black, and so on. For the various kinds of stimulants of sensation are, in their actuality as such, precisely the special sense-objects themselves; and to them the sense-faculty (as a whole) is by nature adapted; so that precisely by their differences is sensation itself differentiated.

On the other hand there are objects which differentiate sensation with respect, not to the kind of agent, but to the mode of its activity. For as sense-qualities affect the senses corporeally and locally, they do so in different ways, if they are qualities of large or small bodies or are diversely situated, i.e. near, or far, or together, or apart. And it is thus that the common sensibles differentiate sensation. Obviously, size and position vary for all the five senses. And not being related to sensation as variations in the immediate factors which bring the sense into act, they do not properly differentiate the sense-faculties; they remain common to several faculties at once.

§ 395. Having seen how we should speak of the absolute or essential sense-objects, both common and-special, it remains to be seen how anything is a sense-object ‘incidentally’. Now for an object to be a sense-object incidentally it must first be connected accidentally with an essential sense-object; as a man, for instance, may happen to be white, or a white thing happen to be sweet. Secondly, it must be perceived by the one who is sensing; if it were connected with the sense-object without itself being perceived, it could not be said to be sensed incidentally. But this implies that with respect to some cognitive faculty of the one sensing it, it is known, not incidentally, but absolutely. Now this latter faculty must be either another sense-faculty, or the intellect, or the cogitative faculty, or natural instinct. I say ‘another sense-faculty’, meaning that sweetness is incidentally visible inasmuch as a white thing seen is in fact sweet, the sweetness being directly perceptible by another sense, i.e. taste.

§ 396. But, speaking precisely, this is not in the fullest sense an incidental sense-object; it is incidental to the sense of sight, but it is essentially sensible. Now what is not perceived by any special sense is known by the intellect, if it be a universal; yet not anything knowable by intellect in sensible matter should be called a sense-object incidentally, but only what is at once intellectually apprehended as soon as a sense-experience occurs. Thus, as soon as I see anyone talking or moving himself my intellect tells me that he is alive; and I can say that I see him live. But if this apprehension is of something individual, as when, seeing this particular coloured thing, I perceive this particular man or beast, then the cogitative faculty (in the case of man at least) is at work, the power which is also called the ‘particular reason’ because it correlates individualised notions, just as the ‘universal reason’ correlates universal ideas.

§ 397. Nevertheless, this faculty belongs to sensitivity; for the sensitive power at its highest—in man, in whom sensitivity is joined to intelligence—has some share in the life of intellect. But the lower animals’ awareness of individualised notions is called natural instinct, which comes into play when a sheep, e.g., recognises its offipring by sight, or sound, or something of that sort.

§ 398. Note, however, that the cogitative faculty differs from natural instinct. The former apprehends the individual thing as existing in a common nature, and this because it is united to intellect in one and the same subject. Hence it is aware of a man as this man, and this tree as this tree; whereas instinct is not aware of an individual thing as in a common nature, but only in so far as this individual thing is the term or principle of some action or passion. Thus a sheep knows this particular lamb, not as this lamb, but simply as something to be suckled; and it knows this grass just in so far as this grass is its food. Hence, other individual things which have no relation to its own actions or passions it does not apprehend at all by natural instinct. For the purpose of natural instinct in animals is to direct them in their actions and passions, so as to seek and avoid things according to the requirements of their nature.

TEXT

418a26–418b26

BOOK II, CHAPTER VII

SIGHT. ITS OBJECT

That of which there is sight is the visible; and the visible is colour, and also something which, ,though it has no name, we can state descriptively. It will be evident what we mean when we have gone further into the matter. § 399

For the visible is colour, and it is this of which visibility is predicated essentially; not, however, by definition, but because :it has in itself the cause of being visible. For every colour is a motivating force upon the actually transparent: this is its very nature. Hence nothing, is visible without light; but by lialit each and everv colour can be seen. Wherefore, we must first decide what light is. §§ 400-3

There is, accordingly, something transparent. By transparent I mean that which is, indeed, visible, yet not of itself, or absolutely, but by virtue of concomitant colour. Air and water and many solids are such. But transparency does not depend on either air or water as such, but on the same quality being found in both, and in the eternal sphere above as well. § 404

Light is the act of this transparency, as such: but in potency this [transparency] is also darkness. Now, light is a kind of colour of the transparent, in so far as this is actualised by fire or something similar to the celestial body; which contains indeed something of one and the same nature as fire. § 405

We have then indicated what the transparent is, and what light is; that light is not fire or any bodily thing, nor any emanation from a body—[if it were this last,] it would be a sort of body, and so be fire or the presence of something similar in the transparent. § 406

For it is impossible for two bodies to exist in the same place at the same time. § 407

Light seems to be the contrary of darkness; and the latter is the privation of this quality in the transparent. So it is plain that the presence of this is light. § 408

Empedocles (or anyone else who may have said the same) was wrong when he said that light was borne along and extended between the earth and its envelope, unperceived by us. This is in contradiction alike to sound reasoning and to appearance. Such a thing might happen unobserved over a small space: but that it should remain unnoticed from the, east to the west is a very extravagant postulate. §§ 409-26

ST. THOMAS’S COMMENTARY

LECTIO FOURTEEN

§ 399. Having distinguished the proper sense-objects from the common, and from those that are sensible incidentally, the Philosopher now treats of the proper object of each sense: first of the proper object of sight; then, at ‘Now let us start’, of that of hearing; then, at ‘It is not so easy’, of that of smell; then, at ‘The tasteable’, of that of taste; and lastly, at ‘The same reasoning holds’, of that of touch.

As to sight, he discusses, first, its object, and then, at ‘At present what is clear’, how this object comes to be seen. Touching the object of sight, he does two things. First, he determines what is the visible, dividing it into two. secondly, he deals with either visible, at ‘For the visible is colour’. He says then, first, that, the proper sense-object being that which each sense perceives of itself exclusively, the sense-object of which the special recipient is sight is the visible. Now in the visible two things are included; for both colour is a visible, and also something else, which can be described in speech, but has no proper name; which visible belongs to things which can be seen by night, such as glow-worms and certain fungi on oak-trees and the like, concerning which the course of this treatise will inform us more clearly as we gain a deeper understanding of the visible; but we have to start from colour which is the more obvious visible.

§ 400. Then, at ‘For the visible’, he begins to define both objects of sight: first colour and then, at ‘Not all visible things’,” that of which he says that it has no proper name. As to colour he does two things: first, he shows what colour has to do with visibility; secondly, at ‘There is, accordingly, something transparent’ he settles what is required for colour to be seen.

First of all, then, he says that, colour being visible, it is visible of itself, for colour as such is essentially visible.

§ 401. ‘Essentially’ is said in two ways. In one way, when the predicate of a proposition falls within the definition of the subject, e.g. ‘man is an animal’; for animal enters into the definition of man. And since that which falls within the definition of anything is in some way the cause of it, in cases such as these the predicate is said to be the cause of the subject. In another way, on the contrary, when the subject of the proposition falls within the definition of the predicate, as when it is said that a nose is snub, or a number is even; for snubness is nothing but a quality of a nose, and evenness of a number which can be halved; and in these cases the subject is a cause of the predicate.

§ 402. Now colour is essentially visible in this second manner, not in the first; for visibility is a quality, as being snub is a quality of a nose. And this is why he says that colour is visible ‘essentially’, but ‘not by definition’; that is to say, not because visibility is placed in its definition, but because it possesses of itself the reason why it should be visible, as a subject possesses in itself the reason for its own peculiar qualities.

§ 403. Which he proves by this, that every colour as such is able to affect what is actually diaphanous. The diaphanous is the same as the transparent (e.g. air or water), and colour has it in its nature to actualise further an actual transparency. And from this, that it affects the actually transparent, it is visible; whence it follows that colour is of its nature visible. And since the transparent is brought to its act only by light, it follows that colour is not visible without light. And therefore before explaining how colour is seen, we must discuss light.

§ 404. Then, at ‘There is, accordingly’, he discusses those things without which colour cannot be seen, namely the transparent and light; and this in three sections. First, he explains the transparent. Secondly, at ‘Light is’, he treats of the transparent’s actuality, i.e. light. Thirdly, he shows how the transparent is receptive of colour, at ‘Now that only can receive colour’.

To begin with, therefore, he says that if colour is that which of its nature affects the transparent, the latter must be, and in fact is, that which has no intrinsic colour to make ie visible of itself, but is receptive of colour from without in a way which renders it somehow visible. Examples of the transparent are air and water and many solid bodies, such as certain jewels and glass. Now, whereas other accidents pertaining to the elements or to bodies constituted from them, are in these bodies on account of the nature of those elements (such as heat and cold, weight and lightness, etc.), transparency does not belong to the nature of air or water as such, but is consequent upon some quality common, not only to air and water, which are corruptible bodies, but also to the celestial bodies, which are perpetual and incorruptible. For at least some of the celestial bodies are manifestly transparent. We should not be able to see the fixed stars of the eighth sphere unless the lower spheres of the planets were transparent or diaphanous. Hence it is evident that to be transparent is not a property consequent on the nature of air or water, but of some more generic nature, in which the cause of transparency is to be found, as we shall see later.

§ 405. Next, at ‘Light etc.’, he explains light, first stating the truth, then dismissing an error. He says, to begin with, that light is the act of the transparent as such. For it is evident that neither air nor water nor anything of that sort is actually transparent unless it is luminous. Of itself the transparent is in potency to both light and darkness (the latter being a privation of light) as primary matter is in potency both to form and the privation of form. Now light is to the transparent as colour is to a body of definite dimensions: each is the act and form of that which receives it. And on this account he says that light is the colour, as it were, of the transparent, in virtue of which the transparent is made actually so by some light-giving body, such as fire, or anything else of that kind, or by a celestial body. For to be full of light and to communicate it is common to fire and to celestial bodies, just as to be diaphanous is common to air and water and the celestial bodies.

§ 406. Then, at ‘We have then indicated’ he rejects a false opinion on light; and this in two stages. First, he shows that light is not a body; then he refutes an objection brought against the arguments which prove that fight is not a body, at ‘Empedocles... was wrong’. As to the first point he does three things.

(a) He states his own view, saying that, once it is clear what the transparent is, and what light is, it is evident that light is neither fire (as some have said, positing three kinds of fire, the combustible, and flame, and light); nor a body at all, or anything flowing from a body, as Democritus supposed, asserting that light consisted of atomic particles emanating from luminous bodies. If there were these emanations from bodies, they would themselves be bodies, or something corporeal, and light would thus be nothing other than fire, or something material of that sort, present in the diaphanous; which is the same’as to say that light is a body or an emanation from a body.

§ 407. (b) At ‘For it is impossible’, he proves his own hypothesis thus. It is impossible for two bodies to be in one place at one time. If therefore light were a body, it could not co-exist with a diaphanous body; but this is false; therefore light is not a body.

§ 408. (c) At ‘Light seems’ he shows that light does co-exist with the diaphanous body. For contraries exist in one and the same subject. But light and darkness are contraries in the manner in which a quality and its privation are contraries, as is stated in the Metaphysics, Book X. Obviously, darkness is a privation of this quality, i.e. of light in the diaphanous body-which is therefore the subject of darkness. Hence tooethe presenct of this quality is light. Therefore light co-exists with the diaphanum.

§ 409. Then at ‘Empedocles... was wrong’ he refutes an answer to one argument which might be urged against those who hold that light is a body. For it is possible to argue thus against them: if light were a body, illumination ought to be a local motion of light passing through the transparent; but no local movement of any body can be sudden or instantaneous; therefore, illumination would be, not instantaneous but successive, according to this view.

§ 410. Of which the contrary is a fact of experience; for in the very instant in which a luminous body becomes present, the transparent it illuminated all at once, not part after part. So Empedocles, and all others of the same opinion, erred in saying that light was borne along by local motion, as a body is; and that it spread out successively through space, which is the medium between the earth and its envelope, i.e. the sky; and that this successive motion escapes our observation, so that the whole of space seems to us to be illuminated simultaneously.

§ 411. For this assertion is irrational. The illumination of the transparent simply and solely presupposes the placing of a luminous body over against the one illumined, with no intervening obstacle.

§ 412. Again, it contradicts appearances. One might indeed allow that successive local motion over a small space could escape our notice; but that a successive movement of light from the eastern to the western horizon should escape our notice is so great an improbability as to appear quite impossible.

§ 413. But as the subject matter under discussion is threefold, i.e. the nature of light, and of transparency, and the necessity of light for seeing, we must take these three questions one by one.

On the nature of light various opinions have been held. Some, as we have seen, held that light was a body; being led to this by certain expressions used in speaking of light. For instance, we are accustomed to say that a ray ‘passes through’ the air, that it is ‘thrown back’, that rays ‘intersect’, and so forth; which all seem to imply something corporeal.

§ 414. But this theory is groundless, as the arguments here adduced of Aristotle show, to which others might easily be added. Thus it is hard to see how a body could be suddenly multiplied over the whole hemisphere, or come into existence or vanish, as light does; nor how the mere intervention of an opaque body should extinguish light in any part of a transparent body if light, itself were a body. To speak of the motion or rebounding of light is to use metaphors, as when we speak of heat ‘proceeding into’ things that are being heated or being ‘thrown back’ when it meets an obstacle.

§ 415. Then there are those who mairitain, on the contrary, that light is spiritual in nature. Otherwise, they say, why should we use the term ‘light’ in speaking of intellectual things? For we say that intellectual things possess a certain intelligible ‘light’. But this also is inadmissible.

§ 416. For it is impossible that any spiritual or intelligible nature should fall within the apprehension of the senses; whose power, being essentially embodied, cannot acquire knowledge of any but bodily things. But if anyone should say that there is a spiritual ‘light’ other than the light that is sense-perceived, we need not quarrel with him; so long as he admits that the light which is senseperceived is not spiritual in nature. For there is no reason why quite different things should not have the same name.

§ 417. The reason, in fact, why we employ ‘light’ and other words referring to vision in matters concerning the intellect is that the sense of sight has a special dignity; it is more spiritual and more subtle than any other sense. This is evident in two ways. First, from the object of sight. For objects fall under sight in virtue of properties which earthly bodies have in common with the heavenly bodies. On the other hand, touch is receptive of properties which are proper to the elements (such as heat and cold and the like); and taste and smell perceive properties that pertain to compound bodies, according as these aie variously compounded of heat and cold, moisture and dryness; sound, again, is due to local movement which, indeed, is also common to earthly and heavenly bodies, but which, in the case of the cause of sound; is a different kind of movement from that of the heavenly bodies, according to the opinion of Aristotle. Hence, from the very nature of the object it would appear that sight is the highest of the senses; with hearing nearest to it, and the others still more remote from its dignity.

§ 418. The same point will appear if we consider the way in which the sense of sight is exercised. In the other senses what is spiritual in their exercise is always accompanied by a material change. I mean by ‘material change’ what happens when a quality is received by a subject according to the material mode A the subject’s own existence, as e.g. when anything is cooled, or heated, or moved about in space; whereas by a ‘spiritual change’ I mean, here, what happens when the likeness of an object is received in the sense-organ, or in the medium between object and organ, as aform, causing knowledge, and not merely as a form in matter. For there is a difference between the mode of being which a sensible form has in the senses and that which it has in the thing sensed. Now in the case of touching and tasting (which is a kind of touching) it is clear that a material change occurs: the organ itself grows hot or cold by contact with a hot or cold object; there is not merely a spiritual change. So too the exercise of smell involves a sort of vaporous exhalation; and that of sound involves movement in space. But seeing involves only a spiritual change-hence its maximum spirituahty; with hearing as the next in this order. These two senses are therefore the most spiritual, and are the only ones under our control. Hence the use we make of what refers to them—and especially of what refers to sight—in speaking of intellectual objects and operations.

§ 419. Then again some have simply identified light with the manifestation of colour. But this is patently untrue in the case of things that shine by night, their colour, nevertheless, remaining obscure.

§ 420. Others, on the other hand, have said that light was the substantial form of the sum, and that the brightness proceeding therefrom (in the form of colours in the air) had the sort of being that belongs to objects causing knowledge as such. But both these propositions are false. The former, because no substantial form is in and of itself an object of sense perception; it can only be intellectually apprehended. And if it is said that what the sense sees in the sun is not light itself but the splendour of light, we need not dispute about names, provided only it be granted that what we call light, i.e. the sight-perceived thing, is not a substantial form. And the latter proposition too is false; because whatever simply has the being of a thing causing knowledge does not, as such, cause material chanee; but the rays from the heavenly bodies do in fact materially affect all things on earth. Hence our own conclusion is that, just as the corporeal elements have certain active qualities through which they affect things materially, so light is the active quality of the heavenly bodies; by their light these bodies are active; and this light is in the third species of quality, like heat.

§ 421. But it differs from heat in this: that light is a quality of the primary change-effecting body, which has no contrary: therefore light has no contrary: whereas there, is a contrary to heat. And because there is no positive contrary to light, there is no place for a contrary disposition in its recipient: therefore, too, its matter, i.e. the transparent body, is always as such immediately disposed to its form. That is why illumination occurs instantaneously, whereas what can become hot only becomes so by degrees. Now this participation or effect of light in a diaphanum is called ‘luminosity’. And if it comes about in a direct line to the lightened body, it is called a ‘ray’; but if it is caused by the reflection of a ray upon a light-receiving body, it is called ‘splendour’. But luminosity is the common name for every effect of light in the diaphanum.

§ 422. So much being admitted as to the nature of light, we can easily understand why certain bodies are always actually lucent, whilst others are diaphanous, and others opaque. Because light is a quality of the primary change-effecting body, which is the most perfect and least material of bodies, those among other bodies which are the most formal and the most mobile to actualisation are always actually lucent; and the next in this order are diaphanous; whilst those that are extremely material, being neither luminous of themselves nor receptive of light, are opaque. One may see this in the elements: fire is lucent by nature, though its light does not appear except in other things. Air and water, being more material, are diaphanous; whilst earth, the most material of all, is opaque.

§ 423. With regard to the third point (the necessity of light for seeing), note that it has been the opinion of some that not merely seeing, but the object of seeing, i.e. colour as such, presupposed the presence of light; that colour as such had no power to affect a transparent medium; that it does this only through light. An indication of this was, they said, that one who stands in the shadow can see what is in the light, but one who stands in the light cannot see what is -in shadow. The cause of this fact, they said, lay in a correspondence between sight and its object: as seeing is a single act, so it must bear on an object formally single; which would not be the case if colour were visible of itself—not in virtue of light—and light also were visible of itself.

§ 424. Now this view is clearly contrary to what Aristotle says here, ‘and... has in itself the cause of being visible’; hence, following his opinion, I say that light is necessary for seeing, not because of colour, in diat it actualises colours (which some say are in only potency so long as they are in darkness), but because of the transparent medium which light renders actual, as the text states.

§ 425. And in proof of this, note that every form is, as such, a principle of effects resembling itself colour, being a form, has therefore of itself the power to impress its likeness on the medium. But note also that there is this difference between the form with a complete, and the form with an incomplete, power to act, that the former is able not merely to impress its likeness on matter, but even to dispose matter to fit it for this likeness; which is beyond the power of the latter. Now the active power of colour is of the latter sort; for it is, in fact, only a kind of light somehow dimmed by admixture of opaque matter. Hence it lacks the power to render the medium fully disposed to receive colour; but this pure light can do.

§ 426. Whence it is also clear that, as light is, in a certain way, the very substance of colour, all visible objects as such share in the same nature:, nor does colour require to be made visible by some other, extrinsic, light. That colours in light are visible to one standing in the shade is due to the medium’s having been sufficiently illumined.

TEXT

418b2–419b27

BOOK II, CHAPTER VII, CONTINUED

SIGHT. HOW COLOUR IS SEEN

 Now that only can receive colour which has none, as only that which is soundless, can re ceive sound. What is without colour is the transparent and the invisible, or what is barely seen, being dark. The transparent is precisely of this nature when it is not in act, but in potency. For the same substance is sometimes dark, sometimes light. §§ 427-8

Not all visible things, however, are visible in light, but only the colour proper to each. There are certain things which are, indeed, not seen in light, but which produce a sensation in darkness, such as those which burn or are luminous. These are not called by any one term. Such are the fungi of certain trees, horn, fish-heads, scales, and eyes. But the colour proper to each of these is not perceived. Why these things are thus seen is matter for another enquiry. §§ 429-30

At present what is dear is that what is seen in light is colour; [and that] therefore it is not seen without light. For to be colour is to be able to move the transparent into act; and this act of the transparent is light. A plain proof whereof is that if one places on the sight itself a coloured object, it is not seen. But colour moves the transparent medium (say, air); and the sensitive organ is moved by this extended continuum. §§ 43 1-2

Democritus. put forward the erroneous opinion that if the medium were a vacuum, perception would be everywhere exact, even of an ant in the sky. This is, however, impossible; for only when the sensitive faculty is affected does vision occur. This cannot, however, be effected by the colour seen, in itself. It must therefore be due to the medium. If there were a vacuum, a thing, so far from being perceived clearly, would not be seen at all. We have stated, then, why it is necessary that colour be seen in light. §§ 433-5

But fire is seen in both darkness and light: necessarily, for the transparent is made light by it. § 436

The same account holds for both sound and smell. No sensation is produced when either of these touches the organ: but a medium is affected by sound and smell, and the sense organ of one or the other sense by the medium. But if one places an object that sounds or smells upon the sense-organ itself, no sensation occurs. The same holds good of touch and taste, although this is not obvious. The reason for this will be made clear later. § 437

The medium of sound is air; that of smell has no special name. For as there is a common quality for colour, to wit, the transparent, in air and water, so there is a common quality in them for smell. For it seems that aquatic animals possess a sense of smell. But man, and whatever living things breathe, are unable to smell except when breathing. The cause of this will be dealt with later. § 438

ST. THOMAS’S COMMENTARY

LECTIO FIFTEEN

§ 427. After treating of colour and the transparent medium and luminosity, the Philosopher now proceeds to explain how the medium is related to colour. It is clear, from the foregoing, that the transparent medium is receptive of colour; for colour, we have seen, acts upon it. Now what is receptive of colour must itself be colourless, as what receives sound must be soundless; for nothing receives what it already has. The transparent medium is therefore colourless.

§ 428. But, as bodies are visible by their colours, the transparent medium must itself be invisible. Yet since one and the same power apprehends contrary qualities, it follows that sight, which apprehends light, also apprehends darkness. Hence, although the transparent medium of itself possesses neither light nor colour, being receptive of both, and is thus not of itself visible in the way that things bright or coloured are visible, it can, all the same, be called visible in the same sort of way as dark things and scarcely visible things are so called. The diaphahum is therefore a kind of darkness, so long as it is not actually but only potentially transparent: the same thing is the subject, sometimes of darkness, sometimes of light. Thus the diaphanum, while it lacks luminosity and is only potentially transparent, is in a state of darkness.

§ 429. Then at ‘Not all’, having decided about colour, which is made visible by light, he reaches a conclusion about that other visible object of which he said above that it had no proper name. He observes that not all things depend on light for being seen, but only the colour that is proper to each particular thing. Some things, e.g. certain animals that appear fiery and lucent in the dark, are not visible in the light, but only in darkness. There are many such things, including the fungi of oaks, the horn of certain beasts and heads of certain fish, and some animals’ scales and eyes. But while all these things are visible in the dark, the colour proper to each is not seen in the dark. The things are seen both in light and in darkness; but in darkness only as bright objects, in light as coloured objects.

§ 430. The reason why they are seen shining in the darkness is another matter. Aristotle only mentions the fact incidentally, in order to show the relation of the visible to luminosity. This, however, seems to be the reason for their being visible in the dark, that such things have in their constitution something of light, inasmuch as the brightness of fire and the transparency of air and water is not entirely smothered in them by the opacity of earth. But having only a small amount of light, their brightness is obscured in the presence of a greater light. Hence in the light they appear not as bright, but only as coloured. The light in their constitution is so weak that it is unable perfectly to actualise the potentially transparent medium to receive the full effect of the colours which by nature it is fitted to receive. Hence, by this light neither their own colour, nor that of other things, is seen: but only their brightness. For brightness, being a more effective agent upon the medium than colour, and in itself more visible, can be seen with less alteration of the medium than colour requires.

§ 431. Next, at ‘At present what is clear’, he explains how colour actually affects sight, first pointing out what this necessarily presupposes, and then, at ‘The same account holds’, indicating a like necessary condition in the case of the other senses. As to the forffier point, he first decides what is the truth of the matter, and then at ‘Democritus etc.’, sets aside an error. First, then, he says that we are now clear that what is seen in light is colour, and that colour is invisible without light; and this because, as has been explained, colour of its nature acts upon a transparent medium, and it does this in,virtue of fight, which is the latter’s actuality. Hence light is necessary if colour is to be seen.

§ 432. An indication of this is the fact that if a coloured body is placed upon the organ of sight it cannot be seen; for then there remains no transparent medium to be affected by the colour. The pupil of the eye is indeed some such medium, but, so long as the coloured body remains placed upon it, it lacks actual transparency. There has to be a medium, say air or something of the kind, which, being actualised by colour, itself acts upon the organ of sight as upon a body continuous with itself For bodies only affect one another through actual contact.

§ 433. Then at ‘Democrituis etc.’, he sets aside an erroneous view. Democritus, he says, was wrong in thinking that if the medium between the eye and the thing seen were a vacuum, any object, however small, would be visible at any distance, e.g. an ant in the sky. This cannot be. For if anything is to be seen it must actually affect the organ of sight. Now it has been shown that this organ as such is not affected by an immediate object—such as an object placed upon the eye. So there must be a medium between organ and object. But a vacuum is not a medium; it cannot receive or transmit effects from the object. Hence through a vacuum nothing would be seen at all.

§ 434. Democritus went wrong because he thought that the reason why distance diminishes visibility was that the medium is of itself an impediment to the action of the visible object upon sight. But it is not so. The transparent medium as such is not in the least incompatible with luminosity or colour; on the contrary, it is proximately disposed to their reception; a sign of which is that it is illumined or coloured instantaneously. The real reason why distance diminishes visibility, is that everything seen is seen within the angle of a triangle, or rather pyramid, whose base is the object seen and apex in the eye that sees.

§ 435. It makes no difference whether seeing takes place by a movement from the eye outwards, so that the lines enclosing the triangle or pyramid run from the eye to the object, or e converso, so long as seeing does involve this triangular or pyramidal figure; which is necessary because, since the object is larger than the pupil of the eye, its effect upon the medium has to be scaled down gradually until it reaches the eye. And, obviously, the longer are the sides of a triangle or pyramid the smaller is the angle at the apex, provided that the base remains the same. The further away, then, is the object, the less does it appear—until at a certain distance it cannot be seen at all.

§ 436. Next, at ‘But fire’, he explains how fire and bright bodies are seen—which are visible not only, like coloured objects, in the light, but even in the dark. There is a necessary reason for this, namely that fire contains enough light to actualise perfectly the transparent medium, so that both itself and other things become visible. Nor does its light fade out in the presence of a greater light, as does that of the objects mentioned above.

§ 437. Then, at ‘The same account’, he shows how the case of the other senses is similar to sight. No sound or odour, e.g., is perceived if there is immediate contact with the organ in question. There must be a medium affected by sound or odour, which itself then. affects our sense of hearing or of smell. A sounding or odorous body placed upon the organ is not perceived as such. The same is true even of touch and taste, though, for a reason to be given later, this is less evident.

§ 438. Finally, at ‘The medium of sound’ he states what is the medium in hearing and smelling. That of hearing is air, and that of smelling is something common to air and water—just as both of these provide a medium for colour in so far as each is a transparency. There is indeed no name for the quality in air and water which provides the medium for odour; but it certainly is not transparency. And that both air and water are conductors of smell he shows from the fact that marine animals have a sense of smell. Man, however, and other animals that walk and breathe, only smell by breathing; which proves that air is the medium of smell. This fact will be explained later.

TEXT

419b3-419b33

BOOK II, CHAPTER VIII

SOUND. ITS CAUSES. ECHO

Now let us start by treating of sound and hearing. Sound is twofold: the sort that is actual, and the sort that is potential. For certain things, we say, have no sound, such as sponges, wool and fur; while others, such as bronze and all other smooth and hard things, have sound, because they are able to produce it, i.e. to cause actual sound in the medium and in the hearing. §§ 439-41

Sound in act is always of something, on something, in something: for it is caused by percussion. Hence it is impossible for anything by itself, as a single thing, to produce sound. For there must be one thing that strikes and another that is struck; hence whatever enlits sound does so ‘on something’. i.e. by contact with something—which, when touched with a blow, sounds. And the blow necessarily implies movement. § 442

As we said before, it is not a blow upon anything whatever that gives sound: wool makes no sound, although it be struck; but bronze, or anything smooth and hollow, is such. Bronze because it is smooth; whilst hollow things by repercussion produce many ‘blows’ after the first, since what is set in motion cannot find an outlet. § 443-4

Further: sound is heard in air and water, but less in water. It is, however, neither air nor water that, properly, sounds; there must be a percussion of solid objects on each other, and on air. This happens if air is confined when struck, and cannot disperse. Hence if the striking is rapid and violent sound results. For the movement of what strikes must be sudden, if it is to out-run the breaking-up of the air; just as if one were to strike a rapidly-moving heap of sand or pile of stones. §§ 445-6

Echo arises when air rebounds like a ball against air rendered a compact unity by a restraining vessel that prevents its dispersion. §§ 447-9

It seems there is always some echo, but not always a clear one. For the same occurs with sound as with light; which also is always, reflected: otherwise it would not spread to every part, but beyond the area illuminated by the sun there would be darkness. Still, it is not [always] reflected as it is reflected by water or bronze or other smooth things; hence it makes the shadow by which we discern the boundaries of light.

ST. THOMAS’S COMMENTARY

LECTIO SIXTEEN

§ 439. Having disposed of the visible, the Philosopher now deals with the audible, that is, withsound. This section divides into two parts. In the first he deals with sound in general. In the second he deals with one kind of sound, namely voice, at ‘Voice’ etc. The first part is again divided into two ‘arts. First, he deals with sound itself; then with difference of sound, at ‘Differences in sonorous things’. The former part again subdivides. First, he reaches a conclusion on sound; then he raises a doubt about this conclusion, at ‘is it that which strikes’. The former of these sections again divides into two conclusions, the first on the origin of sound, and the second on the way that sound affects the hearing, at ‘Empty space’.

Should it be asked why he now raises the question of the origin of sound, whereas he did not deal with the production of colour, but only with colour’s effects on sense-organ and medium, the, answer is that colour and odour and taste and the tangible qualities have a fixed and permanent existence in their subjects. The consideration therefore of these qualities in themselves is one thing, and that of the way they affect the senses is another. The two questions are quite distinct. So the Philosopher deals with the origin of colour, taste and smell in his work De Sensu et Sensato; and with that of tangible qualities in the De Generatione, and in part also in the Meteorologica; whilst in the present book he is only considermig the objects of sensation in so far as they affect the sense-organs. But as sound is caused by change and has no fixed and stable existence in a subject, but actually consists in a movement or change, therefore it can be considered at one and the same time in its objective origin and in its effect on the senses. Its origin, then, is regarded under two aspects: first he deals with the primary origin of sound; and then, at ‘Echo arises’, with its secondary origin, produced by reverberation. As to the primary origin, he first explains that sound is sometimes in act and sometimes in potency; after which he shows how sound comes to be in act, at ‘Sound in act’.

§ 440. He says, then, first that, before dealing with touch and taste, we must consider sound and smell; but first sound, because it is more spiritual, as has been shown. We speak of sound in two ways: as in act and as in potency. We say a thing has a sound when it is actually sounding, and also when it is only able to make sounds; as when we say, ‘this bell sounds well’, though it may not be actually ringing. In the same way we say of some things that they have no sound, meaning that they have no power to produce sound, e.g. sponges and similar soft objects; whereas other things, on the contrary, are said to sound because they are especially apt to produce sound, such as bronze, and other smooth and even materials. So it is clear that sound is sometimes spoken of as potential, and sometimes as actual.

§ 441. But the actuality of sound involves the medium and the faculty of hearing. For we can speak of a sense-object as actual in two ways: (1) So far as the object is actually being sensed, i.e. when its likeness is affecting the sense-organ. In this way a sound is actual when it is heard. (2) So far as the object actually is such that it can be sensed, but is such simply in its own objective being, outside the senses. And in this way the other sense-objects, colour, odour, savour, etc., exist actually in coloured or odorous or savourable bodies. But not so sound; for in a sound-productive body there is sound only potentially: actual sound exists only when the medium is affected by a disturbance from that body. Therefore the act of sound exists, he says, in the medium and in the hearing, but not in the audible body.

§ 442. Then at ‘Sound in act’, Aristotle shows how sound actually comes about: first with regard to the number of factors required for sound to come into act; and then, at ‘As we said before’, with regard to what these factors are. First then, there are three concurrent factors in sound: Sound is ofsomething, on something, in something. Therefore no single thing by itself can produce sound—the reason (or sign) of this being that the cause of sound is percussion, which implies a thing struck and a striker. Hence his saying ‘of something, on something’, i.e. of the thing striking and on the thing struck. What produces sound must touch something as with a sudden blow. Now a blow implies local movement, which implies a medium. Hence the need for a medium, if sound is to be produced actually. Hence his saying, ‘in something’.

§ 443. When he says ‘As we said before’, he shows what sort of factors produce sound. And first he shows of what sort must the striking and the struck objects be; and then, at ‘Further etc.’ what sort of thing the medium must be. First, then, as we have already noted, sound is not produced by striking any material body whatever. Wool and sponges and suchlike soft things cannot give out sound even when struck; the reason being that soft things yield to the impact, so that no air is expelled by it-no air in which a sound might be formed by the blow of a striker and the resistance of something struck. Yet when such soft things are compressed firmly enough to resist an impact, then a sound results, though only a dull one. But bronze objects, and bodies that are smooth and concave, give out sound when struck. Hardness is needed; else air will not be driven out by the blow, and consequently no sound be caused. And the body struck should also be smooth, so that the air expelled may hold compactly together in one, as will be explained below.

§ 444. Hollow bodies give out sound very well, when struck, because they hold the air in, and, as this air first set in motion cannot at once come out, it disturbs the rest of the air, and thus by repercussion the impact and the sounding are multiplied. For this reason also materials with a suitable disposition of air in their composition are especially sonorous, such as bronze and silver; but materials in which air is less well disposed are less sonorous, like lead and such things as are more earthy and sedimentary.

§ 445. Then, at ‘Further: sound is heard’, he explains the medium in which sound is produced: observing that the medium of sound is air or water, but water less than air. The most suitable medium for both the production and the reception of sound is air. And since the medium of any sense must lack all the sensible qualides perceived by that sense, if it is to serve as the receiver of them, it is evident that neither air nor water has a sound of its own; but if sound is to be produced in air or water some firm and solid and hard objects must strike upon one another, and so cause an impact on the air.

§ 446. Now if the impact of solid bodies upon one another is to be simultaneous with the production of sound in the air, it is necessary that the air remain a whole and continuous, that it be not broke up before receiving the effect of the impact. Hence it is, as experience shows that when two bodies are brought slowly together no sound occurs: for the air recedes and melts away before the contact is made. But if the impact is swift and violent, then a sound results; for if sound is to occur, the movement of what strikes must precede the division of the air, so that the air can be struck while still en bloc, or collected, and so a sound be produced in it. It is as when one strikes swiftly with a whip, hitting a whole heap of stones all at once, before they fall apart. For the same reason, when anything passes rapidly through the air, it makes a noise as it goes, because the air itself, being compact, serves as the object struck, not merely as the medium.

§ 447. Next, at ‘Echo arises’, he deals with the secondary production of sound, which is by reverberation. This sound is called echo. He settles, first, how echo itself is produced; and then, at ‘It seems’, how its varieties occur. With regard to the former point, we may note that the production of sound in air follows the movement of air, as has been said. What takes place in the air when sound is produced is like what happens in water when something is thrown into it. Obviously, circular undulations form in the water where it is hit; and these are small around the point of striking, but with a strong movement; whilst further away the undulations are large and the movement is weak. Ultimately, the movement disappears altogether and the undulations cease. But if the undulations meet an obstacle before they cease moving a contrary wave-movement is set up, so much the more violent as it is closer to the original impact.

§ 448. Now, in a similar way, when sounding bodies strike together the air is moved in a circular motion and the sound diffused in all directions. Near to the impact the air-circles are small, but are moving swiftly. Hence, there the sound will be very distinctly heard. Further away the circles are larger and the sound is less distinct; and at length it ceases altogether. But if, before the circles vanish, the air so moving and so carrying sound, is repulsed from some body, the undulations return on their tracks and a new sound comes in the reverse direction. And this is called ‘echo’.

§ 449. This effect is realised most perfectly when the obstacle in question is concave, for then it acts like a vessel that holds the air together in its own unity, preventing its dispersal. For then the moving air, thus held together and unable to move further because of the obstacle, is thrown back on the air behind and a reverse movement begins-just as when a ball thrown against an obstacle rebounds.

§ 450. Then, where he says ‘It seems’, he explains how echo occurs in various ways, saying that there would seem to be always some echo produced, but it is not always definite, i.e. clearly perceptible. This he shows by a simile drawn from light. Light, he says, is always reflected; but sometimes the reflection is perceptible, sometimes not. The reflection of light is visible when it comes from a shining body; for then the reflection is accompanied by some brightness, as was the original emission of light. The reflection is not visible when it comes from an opaque body, for then it takes place with no brightness or radiance. Yet unless the sun’s rays were reflected by opaque bodies there would be no light at all in the air of any part of the upper hemisphere, but instead only darkness everywhere away from the sun, i.e. outside the places reached by the solar rays directly. But light is not reflected by opaque bodies in the same way as by water or air or any of the smooth and polished bodies which throw back light brightly and radiantly. The reflection from opaque bodies is ‘dark’, that is to say, it forms the shadow extending outside the limit of the clear light of the solar rays. So also, then, when the repercussion of sound takes place in a concave body, wherein sound cannot but be multiplied, a clear and distinctly perceptible echo results. But when the repercussion of sound is from other bodies which do not naturally redouble it, there is no perceptible echo.

TEXT

419b33-420b5

BOOK II, CHAPTER VIII, CONTINUED

HEARING. ITS MEDIUM. HIGH AND LOW SOUNDS

Empty syace is rightly said to be necessary for hearing,—for by that is meant air which, when moved as a simple continuum, causes hearing. On account of its ‘instability, however, it gives no sound unless what is struck be smooth; then it has the required unity, holding together on account of the even surface, for the surface of a smooth thing is uniform. The sonorous, therefore, is that which moves a compact mass of air continuous as far as the organ of hearing. §§ 451-452

Hearing is naturally conjoined with air; and because it is in air, therefore by amovement in the air outside is caused an interior movement also. Hence an animal does not hear all over its body, nor does air pass through every member. For the animate body and the part to be set in motion have not air throughout (as [also liquid is only in the eyeball]). § 453

Of itself air is soundless; for, being mobile, it easily yields. But when its motion cannot be diffused a sound arises. There is air, built into the ears, so as to be immobile; and it accordingly registers every variety of motion with exactitude. § 454

On this account therefore we hear also in water, for this does not penetrate to that inner air, nor, by reason of its many convolutions, into the ear. Should it do so, one would not hear; nor if the eardrum were ailing—just as we do not see if the cornea of the pupil is diseased. §§ 455-7

A test of good hearing on the contrary is whether there is a continual ringing in the ear, like a horn. For then the air in the ear is perpetually moving by a motion ofits own; whereas sound is from without, and is not the ear’s own. And for this reason they say that we hear by a “resounding vacuum” because we hear by what holds air in constraint. § 458

Is it that which strikes, or that which is struck, which sounds? Or both, but in different ways? For sound is a movement of something that can move in the way that a bouncing body flies off a smooth surface one flings it at. As has been said, not everything that strikes or is struck gives a sound, for instance one needle struck against another. But what is struck must have a plane surface smooth and regular so that the air rebound and be set in motion instantaneously. §§ 459-60

Differences in sonorous things are apparent in the actu sounding. For just as colours are not seen without light, so there is no high or low note apart from sounding. § 461

These terms are used by metaphor from things perceived by touch. § 462

A high note moves the sense-organ much in a brief space of time; the low note, little, in a longer time. § 463

But this does not mean that the fast is the high and the slow the low; rather, the former arises because of swiftness of motion, the latter because of slowness. § 464

So there seems to be an analogy with the tangible, as sharp and blunt. For the ‘sharp’ pierces, while the ‘blunt’ thuds; and the reason is that the one moves in a brief period, the other in a greater. Hence it comes about that the former is swift, the latter slow.

Let this serve to define sound. § 465

ST. THOMAS’S COMMENTARY

LECTIO SEVENTEEN

§ 451. After deciding about the origin of sound the Philosopher now comes to certain conclusions about sound’s impression on sense: and first, at ‘Hearing’ is etc., about its eftect on the senseorgan. First, then, he observes that, the medium of sound being air, it has been rightly said that the vacuum was an essential factor in hearing (for those who said this thought that ‘the vacuum’ was air). Now when air is disturbed it makes sound audible, provided that it is a single continuum such that a sound can be formed in it. For if sound is to be produced it requires a singleness and continuity in the air; therefore no sound occurs unless the sounding thing that is struck be smooth. A thing is smooth if no part of it juts out from the rest. A smooth surface, then, is a simple unity, upon which the air too exists in a single and uniform way. it is otherwise if the body in question has a rough surface; and since air is ‘unstable’, that is, easily broken up, it follows that neither will the air be a continuous unity, and therefore that no sound will be formed in it.

§ 452. It is clear then that nothing sounds, i.e. produces sound, unless it sets in motion a single continuum of air between itself and the hearing. It follows that those who said that the ‘vacuum’ was adapted to the sense of hearing said something to the point; for to be adapted to hearing is a property of air, which they called a vacuum. But they were not right in using the term ‘vacuum’ for that which is really full of air.

§ 453. Then, when he says ‘Hearing is naturally conjoined’, he concludes about the impression made on hearing by sound, so far as the organ is concerned. And he does three things here. First, he shows that air is adapted to the organ of hearing: secondly, he shows what sort of air this is (at ‘Of itself air’), and thirdly, he shows how hearing may or may not be obstructed by an impediment in the organ (at ‘On this account therefore’).

First, then, he says that hearing has a natural congruity with air; air is adapted to the organ of hearing as watery fluid to the organ of sight. And this because, air pertaining to the organ of hearing, the same effect of sound can exist in the moving air both inside and outside the organ—the air inside acting as the instrument of hearing. This is why hearing does not occur in every part of the body, nor the sounding air produce a sound in, or penetrate into, every part of the animate body. The latter has not air in each of its parts so that any part might be set in motion by sound; in the same way as the living body has a certain watery fluid only in one special part (the pupil of the eye), not everywhere.

§ 454. Then, at ‘Of itself air’, he shows what sort of air is instrumental in hearing. And he says that everything that sounds is by nature resistant to percussion. Obviously air is not of itself a sounding material, for it does not by nature resist what strikes it, but rather yields easily. However, its yielding