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POTENCY

Commentary on the Sentences I, d.42, q.1, a.1

The name potency was first used to signify the power of man, as when we say that some men are powerful... Then the name was transferred to things in nature. Among men he is recognized as potent who can do what be wants with other things and is not impeded; to the extent that he can be impeded, his power is diminished. The potency of someone, or of a natural agent, is impeded (even in the case of a being with volition) insofar as it can be impeded by another. Therefore, as regards the meaning of potency in its first use as a name, the reference is to the not-being affected by another. Hence what cannot be acted upon, even though it cannot act, is called potent, as in the case of something hard which does not have the potency to be cut...

In answer to the first objection we say that the notion of primary potency does not signify matter according to its more proper signification, because, as we said, the name potency was first used to signify a (1) principle of action. Later it was transferred to mean that (2) whatever receives the action of an agent is said to have a potency. This is passive potency, just as the operation or action in which an active potency is completed corresponds to active potency, so what corresponds to passive potency as its perfection and complement is called act.

C.G. I, ch.43

Every act inhering in another is terminated by that in which it inheres, since what is in another is in it according to the mode of the receiver. Hence an act that exists in nothing is terminated by nothing.

De potentia

Existence, as we understand it here, signifies the highest perfection of all: and the proof is that act is always more perfect than potentiality. Now no signate form is understood to be in act unless it be supposed to have being. Thus we may take human nature or fiery nature as existing potentially in matter, or as existing in the power of an agent, or even as in the mind: but when it has existence it becomes actually existent. Wherefore it is clear that existence as we understand it here is the actuality of all acts, and therefore the perfection of all perfections.

Nor may we think that existence, in this sense, can have anything added to it that is more formal and determines it as act determines potentiality: because existence in this latter sense is essentially distinct from that to which it is added and whereby it is determined. But nothing that is outside the range of existence can be added to existence: for nothing is outside its range except non-being, which can be neither form nor matter. Hence existence is not determined by something else as potentiality by act but rather as act by potentiality, since in defining a form we include its proper matter instead of the difference: thus we define a soul as the act of an organic physical body. Accordingly this existence is distinct from that existence inasmuch as it is the existence of this or that nature.

Compendium theologiae, ch. 18, par. 35

No act is found to be limited except through the potency which receives it; thus we find forms limited according to the potency of matter.

S.T. I, q.4, a.1, ad 3

Being (esse) itself is the most perfect of all things, for it is compared to all things as that which is act; for nothing has actuality except so far as it is. Hence being is the actuality of all things, even of forms themselves. Therefore it is not compared to other things (~) as the receiver is to the received, but rather (+) as the received to the receiver. When therefore I speak of the being of man, or of a horse, or of anything else, being is considered as a formal principle, and as something received, and not as that to which being belongs.

S.T. I, q.85, a.7

One may understand the same thing better than someone else, through having a greater power of understanding; just as a man may see a thing better with his bodily sight, whose power is greater and whose sight is more perfect. This same thing applies to the intellect in two ways. First, as regards the intellect itself, which is more perfect. For it is plain that the better the disposition of a body, the better is the soul allotted to it; which clearly appears in things of different species. The reason for this is that act and form are received into matter according to the capacity of matter; and thus because some men have bodies of better disposition, their souls have a greater power of understanding.