Summa Theologica, Part I (Prima Pars) From the Complete...

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.

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 Obj. 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 Obj. 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 Obj. 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. _______________________

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.

Obj. 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.

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.

Reply Obj. 1: As we have said above (Q. 7, A. 1), God is called infinite, because He is a form unlimited by matter; whereas in material things, the term "infinite" is applied to that which is deprived of any formal term. And form being known in itself, whereas matter cannot be known without form, it follows that the material infinite is in itself unknowable. But the formal infinite, God, is of Himself known; but He is unknown to us by reason of our feeble intellect, which in its present state has a natural aptitude for material objects only. Therefore we cannot know God in our present life except through material effects. In the future life this defect of intellect will be removed by the state of glory, when we shall be able to see the Essence of God Himself, but without being able to comprehend Him.

Reply Obj. 2: The nature of our mind is to know species abstracted from phantasms; therefore it cannot know actually or habitually species of numbers or figures that are not in the imagination, except in a general way and in their universal principles; and this is to know them potentially and confusedly.

Reply Obj. 3: If two or more bodies were in the same place, there would be no need for them to occupy the place successively, in order for the things placed to be counted according to this succession of occupation. On the other hand, the intelligible species enter into our intellect successively; since many things cannot be actually understood at the same time: and therefore there must be a definite and not an infinite number of species in our intellect.

Reply Obj. 4: As our intellect is infinite in power, so does it know the infinite. For its power is indeed infinite inasmuch as it is not terminated by corporeal matter. Moreover it can know the universal, which is abstracted from individual matter, and which consequently is not limited to one individual, but, considered in itself, extends to an infinite number of individuals. _______________________

Obj. 2: Further, as stated in Phys. iv, 12, "what sometimes is and sometimes is not, is measured by time." Now the intellect abstracts from time, and from other material conditions. Therefore, as it is proper to a contingent thing sometime to be and sometime not to be, it seems that contingent things are not known by the intellect.

On the contrary, All knowledge is in the intellect. But some sciences are of the contingent things, as the moral sciences, the objects of which are human actions subject to free-will; and again, the natural sciences in as far as they relate to things generated and corruptible. Therefore the intellect knows contingent things.

I answer that, Contingent things can be considered in two ways; either as contingent, or as containing some element of necessity, since every contingent thing has in it something necessary: for example, that Socrates runs, is in itself contingent; but the relation of running to motion is necessary, for it is necessary that Socrates move if he runs. Now contingency arises from matter, for contingency is a potentiality to be or not to be, and potentiality belongs to matter; whereas necessity results from form, because whatever is consequent on form is of necessity in the subject. But matter is the individualizing principle: whereas the universal comes from the abstraction of the form from the particular matter. Moreover it was laid down above (A. 1) that the intellect of itself and directly has the universal for its object; while the object of sense is the singular, which in a certain way is the indirect object of the intellect, as we have said above (A. 1). Therefore the contingent, considered as such, is known directly by sense and indirectly by the intellect; while the universal and necessary principles of contingent things are known only by the intellect. Hence if we consider the objects of science in their universal principles, then all science is of necessary things. But if we consider the things themselves, thus some sciences are of necessary things, some of contingent things.