Commentaria in Summam contra Gentiles, Liber I

Having shown that God is intelligent, it is further shown that He is His own act of understanding¹. Saint Thomas proposes the conclusion, saying that from the fact that God is intelligent, it follows that His understanding is His essence.

I. And he argues first as follows. Whatever is in God is the divine essence. But God's understanding is in God, since it is an immanent action, not one that alters the intelligible object. Therefore it is His essence. Now the divine essence and the divine esse are God Himself. Therefore, and so on.

It must be noted that when Saint Thomas says that because God is intelligent, it follows that His understanding is His essence, this consequent does not follow formally from the antecedent. For if it followed formally — God is intelligent; therefore His understanding is His essence — then in every intelligent being its understanding would be its essence. But it follows only on account of the matter, from the fact that whatever is in God is God. Hence the word "follows" here signifies concomitance rather than formal dependence. For the sense is that in God there accompanies the being intelligent an identity of the act of understanding with the one understanding.

II. Second. Divine esse is his essence. Therefore divine understanding is his intellect. Therefore it is his essence. — The first consequence is proved: because understanding is related to intellect just as esse is to essence. — The second, however: because his intellect is his essence, since there is no accident in God.

It should be noted that there is a difference between transient and immanent operations, because transient operations are not intrinsic perfections of the agent but of the patient; immanent operations, however, are perfections and actualities of the agent. And from this it is taken that understanding, which is an immanent operation, is compared to intellect as esse is to essence. For just as esse signifies the ultimate actuality and intrinsic perfection by which something is completively in the genus of beings, so understanding is the ultimate intrinsic perfection of the intellect, by which it is completively and actually in the genus of intelligibles. For the intellect, considered as informed only by the intelligible species and not actually understanding, is assimilated to a thing having form in that prior state in which it is considered as united to matter and not yet giving it esse but constituting its proper receptive esse². Therefore, just as a thing having form in that prior state according to the consideration of the intellect does not yet have the ultimate actuality and perfection of being, so the intellect in that prior state before understanding is considered as not yet completely in act in the genus of intelligibles. But through understanding itself it is completed in act, and moreover, as such, it no longer remains in potency.

III. Third. If it were not so, something would be more perfect and nobler than God's essence. And thus God would not be the first and most perfect being. — The consequence is proved: because a second act is more perfect than a first act, as consideration than knowledge—namely, where the second act is really distinct from the first. But the knowledge and intellect of God are the same as His essence. Therefore that act will be more perfect than the divine essence.