Objection 1. It seems that God does not know enunciable things. For to know enunciable things belongs to our intellect as it composes and divides. But in the divine intellect, there is no composition. Therefore God does not know enunciable things.
Objection 2. Further, every kind of knowledge is made through some likeness. But in God there is no likeness of enunciable things, since He is altogether simple. Therefore God does not know enunciable things.
On the contrary, It is written: "The Lord knoweth the thoughts of men" (Psalm 93:11). But enunciable things are contained in the thoughts of men. Therefore God knows enunciable things.
I answer that, Since it is in the power of our intellect to form enunciations, and since God knows whatever is in His own power or in that of creatures, as said above (Article 9), it follows of necessity that God knows all enunciations that can be formed.
Now just as He knows material things immaterially, and composite things simply, so likewise He knows enunciable things not after the manner of enunciable things, as if in His intellect there were composition or division of enunciations; for He knows each thing by simple intelligence, by understanding the essence of each thing; as if we by the very fact that we understand what man is, were to understand all that can be predicated of man. This, however, does not happen in our intellect, which discourses from one thing to another, forasmuch as the intelligible species represents one thing in such a way as not to represent another. Hence when we understand what man is, we do not forthwith understand other things which belong to him, but we understand them one by one, according to a certain succession. On this account the things we understand as separated, we must reduce to one by way of composition or division, by forming an enunciation. Now the species of the divine intellect, which is God's essence, suffices to represent all things. Hence by understanding His essence, God knows the essences of all things, and also whatever can be accidental to them.
Reply to Objection 1. This objection would avail if God knew enunciable things after the manner of enunciable things.
Reply to Objection 2. Enunciatory composition signifies some existence of a thing; and thus God by His existence, which is His essence, is the similitude of all those things which are signified by enunciation.
Source: Summa Theologica (New Advent)