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.

So we say that God sees Himself in Himself, because He sees Himself
through His essence; and He sees other things not in themselves, but
in Himself; inasmuch as His essence contains the similitude of things
other than Himself.

Reply Obj. 1: The passage of Augustine in which it is said that God
"sees nothing outside Himself" is not to be taken in such a way, as
if God saw nothing outside Himself, but in the sense that what is
outside Himself He does not see except in Himself, as above explained.

Reply Obj. 2: The object understood is a perfection of the one
understanding not by its substance, but by its image, according to
which it is in the intellect, as its form and perfection, as is said
in _De Anima_ iii. For "a stone is not in the soul, but its image."
Now those things which are other than God are understood by God,
inasmuch as the essence of God contains their images as above
explained; hence it does not follow that there is any perfection in
the divine intellect other than the divine essence.

Reply Obj. 3: The intellectual act is not specified by what is
understood in another, but by the principal object understood in which
other things are understood. For the intellectual act is specified by
its object, inasmuch as the intelligible form is the principle of the
intellectual operation: since every operation is specified by the form
which is its principle of operation; as heating by heat. Hence the
intellectual operation is specified by that intelligible form which
makes the intellect in act. And this is the image of the principal
thing understood, which in God is nothing but His own essence in which
all images of things are comprehended. Hence it does not follow that
the divine intellectual act, or rather God Himself, is specified by
anything else than the divine essence itself.
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SIXTH ARTICLE [I, Q. 14, Art. 6]

Whether God Knows Things Other Than Himself by Proper Knowledge?

Objection 1: It seems that God does not know things other than
Himself by proper knowledge. For, as was shown (A. 5), God knows
things other than Himself, according as they are in Himself. But
other things are in Him as in their common and universal cause, and
are known by God as in their first and universal ca