IDENTITY BETWEEN GOD AND HIS INTELLIGENCE
God must be His own intelligence. Since "to understand" is second act, for example, to consider, whereas the corresponding first act is the intellect or knowledge, any intellect that is not its own understanding is related to its understanding as potency to act. For in the order of potencies and acts, what is first is always potential with respect to what follows, and what is last is perfective. This is true only with reference to one and the same being, for among different beings the converse obtains; thus a mover and an agent are related to the thing moved and actuated as act to potency. In God, however, who is pure act, there is nothing that is related to anything else as potency to act. Accordingly God must be His own intelligence.
Furthermore, the intellect is related to its act of understanding as essence is related to existence. But God understands through His essence, and His essence is His existence. Therefore His intellect is His act of understanding. And thus no composition is attributed to Him by the fact that He understands, since in Him intellect and understanding and intelligible species are not distinct; and these in turn are nothing else than His essence.