When several things are ordained to one thing, one of them must rule or govern and the rest be
ruled or governed, as the Philosopher, teaches in the Politics. This is evident in the union of soul
and body, for the soul naturally commands and the body obeys. The same thing is true of the
soul’s powers, for the concupiscible and irascible appetites are ruled in a natural order by reason.
Now all the sciences and arts are ordained to one thing, namely, to man’s perfection, which is
happiness. Hence one of these sciences and arts must be the mistress of all the others, and this
rightly lays claim to the name wisdom; for it is the office of the wise man to direct others.
We can discover which science this is and the sort of things with which it deals by carefully
examining the qualities of a good ruler; for just as men of superior intelligence are naturally the
rulers and masters of others, whereas those of great physical strength and little intelligence are
naturally slaves, as the Philosopher says in the aforementioned book in a similar way that science
which is intellectual in the highest degree should be naturally the ruler of the others. This science
is the one which treats of the most intelligible objects.
Now the phrase “most intelligible objects” can be understood in three ways. First, from the
viewpoint of the order of knowing; for those things from which the intellect derives certitude
seem to be more intelligible. Therefore, since the certitude of science is acquired by the intellect
knowing causes, a knowledge of causes seems to be intellectual in the highest degree. Hence that
science which considers first causes also seems to be the ruler of the others in the highest degree.
Second, this phrase can be understood by comparing the intellect with the senses; for while
sensory perception is a knowledge of particulars, the intellect seems to differ from sense by
reason of the fact that it comprehends universals. Hence that science is pre-eminently intellectual
which deals with the most universal principles. These principles are being and those things which
naturally accompany being, such as unity and plurality, potency and act. Now such principles
should not remain entirely undetermined, since without them complete knowledge of the
principles which are proper to any genus or species cannot be had. Nor again should they be dealt
with in any one particular science, for, since a knowledge of each class of beings stands in need
if such principles, they would with equal reason be investigated in every particular science. It
follows, then, that such principles should be treated by one common science, which, since it is
intellectual in the highest degree, is the mistress of the others.
Third, this phrase can be understood from the viewpoint of the intellect’s own knowledge. For
since each thing has intellective power by virtue of being free from matter, those things must be
intelligible in the highest degree which are altogether separate, from matter. For the intellect and
the intelligible object must be proportionate to each other and must belong to the same genus,
since the intellect and the intelligible object are one in act. Now those things are separate from
matter in the highest degree which abstract not only from signate matter (as the natural forms
taken universally of which the philosophy of nature treats) but from sensible matter altogether;
and these are separate from matter not only in their intelligible constitution (ratio), as the objects
of mathematics, but also in being (esse), as God and the intelligences. Therefore the science
which considers such things seems to be the most intellectual and the ruler or mistress of the
Now this threefold consideration should be assigned to one and the same science and not to
different sciences, because the aforementioned separate substances are the universal and first
causes of being. Moreover, it pertains to one and the same science to consider both the proper
causes of some genus and the genus itself; for example, the philosophy of nature considers the
principles of a natural body. Therefore, it must be the office of one and the same science to
consider the separate substances and being in general (ens commune), which is the genus of
which the aforementioned substances are the common and universal causes.
From this it is evident that, although this science (metaphysics or first philosophy) studies the
three things mentioned above, it does not investigate any one of them as its subject, but only
being in general. For the subject of a science is the genus whose causes and properties we seek,
and not the causes themselves of the particular genus studied; for a knowledge of the causes of
some genus is the goal to which the investigation of a science attains. Now although the subject
of this science is being in general, the whole of it is predicated of those things which are separate
from matter both in their intelligible constitution and in being. For it is not only those things
which can never exist in matter that are said to be separate from matter in their intelligible
constitution and being, such as God and the intellectual substances, but also those which can
exist without matter, as being in general. This could not be the case, however, if their being
depended on matter.
Therefore in accordance with the three things mentioned above from which this science derives
its perfection, three names arise. It is called divine science or theology inasmuch as it considers
the aforementioned substances. It is called metaphysics inasmuch as it considers being and the
attributes which naturally accompany being (for things which transcend the physical order are
discovered by the process of analysis, as the more common are discovered after the less
common). And it is called first philosophy inasmuch as it considers the first causes of things.
Therefore it is evident what the subject of this science is, and how it is related to the other
sciences, and by what names it is designated.