WHAT OUR INTELLECT KNOWS IN MATERIAL THINGS (FOUR ARTICLES)
We now have to consider what our intellect knows in material things. Under this head there are four points of inquiry:
(1) Whether it knows singulars?
(2) Whether it knows the infinite?
(3) Whether it knows contingent things?
(4) Whether it knows future things?
Whether our intellect knows singulars?
Objection 1: It would seem that our intellect knows singulars. For whoever knows composition, knows the terms of composition. But our intellect knows this composition; "Socrates is a man": for it belongs to the intellect to form a proposition. Therefore our intellect knows this singular, Socrates.
Objection 2: Further, the practical intellect directs to action. But action has relation to singular things. Therefore the intellect knows the singular.
Objection 3: Further, our intellect understands itself. But in itself it is a singular, otherwise it would have no action of its own; for actions belong to singulars. Therefore our intellect knows singulars.
Objection 4: Further, a superior power can do whatever is done by an inferior power. But sense knows the singular. Much more, therefore, can the intellect know it.
On the contrary, The Philosopher says (Phys. i, 5), that "the universal is known by reason; and the singular is known by sense."
I answer that, Our intellect cannot know the singular in material things directly and primarily. The reason of this is that the principle of singularity in material things is individual matter, whereas our intellect, as have said above (Q[85], A[1]), understands by abstracting the intelligible species from such matter. Now what is abstracted from individual matter is the universal. Hence our intellect knows directly the universal only. But indirectly, and as it were by a kind of reflection, it can know the singular, because, as we have said above (Q[85], A[7]), even after abstracting the intelligible species, the intellect, in order to understand, needs to turn to the phantasms in which it understands the species, as is said De Anima iii, 7. Therefore it understands the universal directly through the intelligible species, and indirectly the singular represented by the phantasm. And thus it forms the proposition "Socrates is a man." Wherefore the reply to the first objection is clear.
Reply to Objection 2: The choice of a particular thing to be done is as the conclusion of a syllogism formed by the practical intellect, as is said Ethic. vii, 3. But a singular proposition cannot be directly concluded from a universal proposition, except through the medium of a singular proposition. Therefore the universal principle of the practical intellect does not move save through the medium of the particular apprehension of the sensitive part, as is said De Anima iii, 11.
Reply to Objection 3: Intelligibility is incompatible with the singular not as such, but as material, for nothing can be understood otherwise than immaterially. Therefore if there be an immaterial singular such as the intellect, there is no reason why it should not be intelligible.
Reply to Objection 4: The higher power can do what the lower power can, but in a more eminent way. Wherefore what the sense knows materially and concretely, which is to know the singular directly, the intellect knows immaterially and in the abstract, which is to know the universal.
Whether our intellect can know the infinite?
Objection 1: It would seem that our intellect can know the infinite. For God excels all infinite things. But our intellect can know God, as we have said above (Q[12], A[1]). Much more, therefore, can our intellect know all other infinite things.
Objection 2: Further, our intellect can naturally know "genera" and "species." But there is an infinity of species in some genera, as in number, proportion, and figure. Therefore our intellect can know the infinite.
Objection 3: Further, if one body can coexist with another in the same place, there is nothing to prevent an infinite number of bodies being in one place. But one intelligible species can exist with another in the same intellect, for many things can be habitually known at the same time. Therefore our intellect can have an habitual knowledge of an infinite number of things.
Objection 4: Further, as the intellect is not a corporeal faculty, as we have said (Q[76], A[1]), it appears to be an infinite power. But an infinite power has a capacity for an infinite object. Therefore our intellect can know the infinite.
On the contrary, It is said (Phys. i, 4) that "the infinite, considered as such, is unknown."
I answer that, Since a faculty and its object are proportional to each other, the intellect must be related to the infinite, as is its object, which is the quiddity of a material thing. Now in material things the infinite does not exist actually, but only potentially, in the sense of one succeeding another, as is said Phys. iii, 6. Therefore infinity is potentially in our mind through its considering successively one thing after another: because never does our intellect understand so many things, that it cannot understand more.
On the other hand, our intellect cannot understand the infinite either actually or habitually. Not actually, for our intellect cannot know actually at the same time, except what it knows through one species. But the infinite is not represented by one species, for if it were it would be something whole and complete. Consequently it cannot be understood except by a successive consideration of one part after another, as is clear from its definition (Phys. iii, 6): for the infinite is that "from which, however much we may take, there always remains something to be taken." Thus the infinite could not be known actually, unless all its parts were counted: which is impossible.
For the same reason we cannot have habitual knowledge of the infinite: because in us habitual knowledge results from actual consideration: since by understanding we acquire knowledge, as is said Ethic. ii, 1. Wherefore it would not be possible for us to have a habit of an infinity of things distinctly known, unless we had already considered the entire infinity thereof, counting them according to the succession of our knowledge: which is impossible. And therefore neither actually nor habitually can our intellect know the infinite, but only potentially as explained above.