Thomas Aquinas - Summa Theologica, Part I (Prima Pars)

I answer that, God perfectly comprehends Himself, as can be thus proved. A thing is said to be comprehended when the end of the knowledge of it is attained, and this is accomplished when it is known as perfectly as it is knowable; as, for instance, a demonstrable proposition is comprehended when known by demonstration, not, however, when it is known by some probable reason. Now it is manifest that God knows Himself as perfectly as He is perfectly knowable. For everything is knowable according to the mode of its own actuality; since a thing is not known according as it is in potentiality, but in so far as it is in actuality, as said in Metaph. ix. Now the power of God in knowing is as great as His actuality in existing; because it is from the fact that He is in act and free from all matter and potentiality, that God is cognitive, as shown above (AA. 1, 2). Whence it is manifest that He knows Himself as much as He is knowable; and for that reason He perfectly comprehends Himself.

Reply Obj. 1: The strict meaning of "comprehension" signifies that one thing holds and includes another; and in this sense everything comprehended is finite, as also is everything included in another. But God is not said to be comprehended by Himself in this sense, as if His intellect were a faculty apart from Himself, and as if it held and included Himself; for these modes of speaking are to be taken by way of negation. But as God is said to be in Himself, forasmuch as He is not contained by anything outside of Himself; so He is said to be comprehended by Himself, forasmuch as nothing in Himself is hidden from Himself. For Augustine says (De Vid. Deum. ep. cxii), "The whole is comprehended when seen, if it is seen in such a way that nothing of it is hidden from the seer."

Reply Obj. 2: When it is said, "God is finite to Himself," this is to be understood according to a certain similitude of proportion, because He has the same relation in not exceeding His intellect, as anything finite has in not exceeding finite intellect. But God is not to be called finite to Himself in this sense, as if He understood Himself to be something finite. _______________________

FOURTH ARTICLE [I, Q. 14, Art. 4]

Whether the Act of God's Intellect Is His Substance?

Objection 1: It seems that the act of God's intellect is not His substance. For to understand is an operation. But an operation signifies something proceeding from the operator. Therefore the act of God's intellect is not His substance.

Obj. 2: Further, to understand one's act of understanding, is to understand something that is neither great nor chiefly understood, but secondary and accessory. If therefore God be his own act of understanding, His act of understanding will be as when we understand our act of understanding: and thus God's act of understanding will not be something great.

Obj. 3: Further, every act of understanding means understanding something. When therefore God understands Himself, if He Himself is not distinct from this act of understanding, He understands that He understands Himself; and so on to infinity. Therefore the act of God's intellect is not His substance.

On the contrary, Augustine says (De Trin. vii), "In God to be is the same as to be wise." But to be wise is the same thing as to understand. Therefore in God to be is the same thing as to understand. But God's existence is His substance, as shown above (Q. 3, A. 4). Therefore the act of God's intellect is His substance.

I answer that, It must be said that the act of God's intellect is His substance. For if His act of understanding were other than His substance, then something else, as the Philosopher says (Metaph. xii), would be the act and perfection of the divine substance, to which the divine substance would be related, as potentiality is to act, which is altogether impossible; because the act of understanding is the perfection and act of the one understanding. Let us now consider how this is. As was laid down above (A. 2), to understand is not an act passing to anything extrinsic; for it remains in the operator as his own act and perfection; as existence is the perfection of the one existing: just as existence follows on the form, so in like manner to understand follows on the intelligible species. Now in God there is no form which is something other than His existence, as shown above (Q. 3). Hence as His essence itself is also His intelligible species, it necessarily follows that His act of understanding must be His essence and His existence.

Thus it follows from all the foregoing that in God, intellect, and the object understood, and the intelligible species, and His act of understanding are entirely one and the same. Hence when God is said to be understanding, no kind of multiplicity is attached to His substance.

Reply Obj. 1: To understand is not an operation proceeding out of the operator, but remaining in him.

Reply Obj. 2: When that act of understanding which is not subsistent is understood, something not great is understood; as when we understand our act of understanding; and so this cannot be likened to the act of the divine understanding which is subsistent.

Thus appears the Reply to the Third Objection. For the act of divine understanding subsists in itself, and belongs to its very self and is not another's; hence it need not proceed to infinity. _______________________

FIFTH ARTICLE [I, Q. 14, Art. 5]

Whether God Knows Things Other Than Himself?

Objection 1: It seems that God does not know things besides Himself.

For all other things but God are outside of God. But Augustine says

(Octog. Tri. Quaest. qu. xlvi) that "God does not behold anything out

of Himself." Therefore He does not know things other than Himself.

Obj. 2: Further, the object understood is the perfection of the one who understands. If therefore God understands other things besides Himself, something else will be the perfection of God, and will be nobler than He; which is impossible.

Obj. 3: Further, the act of understanding is specified by the intelligible object, as is every other act from its own object. Hence the intellectual act is so much the nobler, the nobler the object understood. But God is His own intellectual act. If therefore God understands anything other than Himself, then God Himself is specified by something else than Himself; which cannot be. Therefore He does not understand things other than Himself.

On the contrary, It is written: "All things are naked and open to His eyes" (Heb. 4:13).

I answer that, God necessarily knows things other than Himself. For it is manifest that He perfectly understands Himself; otherwise His existence would not be perfect, since His existence is His act of understanding. Now if anything is perfectly known, it follows of necessity that its power is perfectly known. But the power of anything can be perfectly known only by knowing to what its power extends. Since therefore the divine power extends to other things by the very fact that it is the first effective cause of all things, as is clear from the aforesaid (Q. 2, A. 3), God must necessarily know things other than Himself. And this appears still more plainly if we add that the very existence of the first effective cause—viz. God—is His own act of understanding. Hence whatever effects pre-exist in God, as in the first cause, must be in His act of understanding, and all things must be in Him according to an intelligible mode: for everything which is in another, is in it according to the mode of that in which it is.

Now in order to know how God knows things other than Himself, we must consider that a thing is known in two ways: in itself, and in another. A thing is known in itself when it is known by the proper species adequate to the knowable object; as when the eye sees a man through the image of a man. A thing is seen in another through the image of that which contains it; as when a part is seen in the whole by the image of the whole; or when a man is seen in a mirror by the image in the mirror, or by any other mode by which one thing is seen in another.