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).