Commentaria in Summam contra Gentiles, Liber II

After St. Thomas had determined the question of the cognition of separate substance with respect to the first act, he now determines it with respect to the second act¹.

I. And he posits this conclusion: The intellect of a separate substance is always actually understanding. This conclusion is to be understood not only with respect to first act, but also with respect to second act, as the arguments show; yet not in this sense, that it always actually knows all knowable things, but because it is always in some actual consideration.

The first is proved as follows. The intellect of a separate substance is above time. Therefore it is not at one time actually understanding and at another time in potency. — The consequence is proved. For what is at one time in act and at another time in potency is measured by time.

Concerning this argument, it must be noted that we must speak one way of the act of understanding considered absolutely in separate substances, and another way of that act as terminated to this or that determinate object in particular. For if a separate substance at some time had no act of understanding at all, so that it would be wholly in potency as regards understanding, and afterwards came to understand actually, it would pass from accidental potency entirely to act; and thus it would change, since in no way would it previously possess the perfection which it would then come to receive anew. If, however, it were not lacking the act of understanding simply, but always understood something actually, though not always this determinate thing, it would be said to pass from potency to act in a certain respect, inasmuch as it would have an act which previously it did not have under this particular aspect; yet it would not be said to pass from potency to act simply, such that it would become an actually understanding being from a potentially understanding one, because it would always be actually understanding, though not always understanding this determinate thing, say a stone. So too among us: when a man who is asleep and considering nothing at all afterwards awakens and begins to consider actually, he is said to pass from potency to act simply, and from leisure to operation; but if, after having been in actual consideration of something, he ceases to consider it and begins to contemplate something else, he is not said to pass from potency to act of considering simply, or from leisure to operation, although this can be said of him in a certain respect. Hence Saint Thomas says below, in the last chapter of this Second Book, that since in the intellect of a separate substance there is a succession of intelligibles, there is no motion properly speaking there: for what succeeds is not the act of a potency, but act succeeding to act.

Therefore the proposition of Saint Thomas in which it is said that that which is sometimes in act and sometimes in potency is measured by time is understood of that which is simply in potency and afterwards comes to be in act. For when there is a passage from potency to act, there is change in some way, and every change is subject to time, or to an instant of time, namely of the continuous; but not when the passage is made from one act to another, as such.

II. Second. Separate substances are living substances. Nor do they have any operation of life other than understanding. Therefore, by their nature, they are always actually understanding. — The consequence is proved. Because every living substance has some operation of life in act, belonging to it by its nature and present in it always: as nutrition in animals.

Concerning the second part of the antecedent, note that when it is said that a separate substance has no operation except understanding, by understanding every operation of the intellective part is meant, and not the act of intellect alone as distinguished against the act of the will. He calls every act of the intellective part understanding, both because the intellective part takes its denomination from it, and because the other operation, which belongs to the will, follows upon it, and thus in positing understanding one also posits willing.

2. Third. Separate substances, according to the philosophers, move the heavenly bodies through intellect. Therefore, etc. — The consequence is evident. Because that motion is always continuous.

Even if the celestial bodies are not posited to move, the same conclusion follows. For if the proper operation of a celestial body, which is its motion, is continuous, much more so is the proper operation of the separate substances, which is understanding, since they are higher than the celestial bodies.

3. Fourth. Separate substances are not moved, neither per se nor per accidens, since they are neither bodies nor powers in a body. Therefore, etc. — The consequence is proved. Because everything that at some time acts, at some time does not act, is moved either per se or per accidens: as is clear in us, as is said in Book VIII of the Physics.

Note that this argument is taken from Book VIII of the Physics, where, at text 51, Aristotle shows that an animal is sometimes moved of itself and sometimes at rest, insofar as it is moved by something else, and sometimes is not moved. For Saint Thomas argues in the same way here: since understanding is the operation of an intellectual substance to which it is naturally ordered, the fact that it sometimes befits it and sometimes does not befit it can arise only because that separate substance is itself sometimes moved and sometimes not moved; for it is sometimes disposed in one way and sometimes in another.

But if it were said that this can be done by the freedom of the will, according to which at one time it wills to understand and at another time wills not to understand: — the answer is that freedom does not operate toward understanding or not understanding separate substances absolutely, though it does operate toward understanding or not understanding this determinate thing or that. The reason for this is: because the intellect is naturally ordered to the act of understanding, it already understands itself and God naturally, but other things freely.