See Ch. XXXIX, and B. I, Ch. XIV, note.
In later life, St Thomas wrote more cautiously on this subject. What he means is this. I call God, let us say, 'intelligent.' And so He is intelligent. He is, if I may use a vulgar expression, 'getting on that way' which I call the way of intelligence; only, He goes so on in it, that the poor little beginning of intelligence, which is all that I can master and appreciate as such, is wholly unfit to stand for His infinite intelligence. -- To put the same in a more learned way. God to me is not bounded in this, which I understand, but he is this-like, and still more this-like to infinity. To express the fact, I may call God, and truly call Him, this (e.g., 'intelligent'); but I may as truly (though not always as safely to unintelligent ears) deny the same of Him, merely meaning by the denial that the this, though the best and truest word we have, is a wholly inadequate expression to contain and represent Him, who "is not mere Being, but even beyond Being in dignity and power" (Plato, Rep. 5O9 b). Here we have what St Thomas (B. I, Ch. XIV) calls via remotionis.
Of God and His Creatures: 3.49