Summa contra Gentiles1.49 Chapter XLIX. That God knows things other than himself

From the fact that God knows Himself first and per se, we must conclude that He knows things other than Himself in Himself.

For the knowledge of an effect is sufficiently obtained from knowledge of the cause: Wherefore we are said to know a thing when we know its cause. Now God by His essence is the cause of being in other things. Since therefore He knows His own essence most fully, we must conclude that He knows other things also.

Further. The likeness of every effect pre-exists somewhat in its cause: since every agent produces its like. Now whatever is in something else, is therein according to the mode of the thing in which it is. If, therefore, God is the cause of certain things, since by His nature He is intellectual, the likeness of His effect will be in Him intelligibly. Now that which is in a subject intelligibly, is understood thereby. Therefore God understands things other than Himself in Himself.

Moreover. Whoever knows a thing perfectly, knows whatever can be said truly of that thing, and whatever is becoming thereto by its nature. Now it is becoming to God by His nature to be the cause of other things. Since then He knows Himself perfectly, He knows that He is a cause: and this is impossible unless He knows His effect somewhat. Now this is something other than Himself, for nothing is cause of itself. Therefore God knows things other than Himself.

Accordingly taking these two conclusions together, it is evident that God knows Himself as the first and per se object of His knowledge, and other things as seen in His essence.

This truth is explicitly declared by Dionysius (Div. Nom. vii.) as follows: He looks upon singulars not by i Poster. Anal. ii. i. 2 Cf. ch. xlviii.

casting His eye on each one, but He knows all things as one, contained in their cause; and further on: Divine wisdom knows other things by knowing itself.

Moreover the authority of Holy Writ apparently bears witness to the same statement. For in the psalm it is said of God: He hath looked forth from His high sanctuary, as though He saw other things from His exalted self.