"Things are intelligible accordingly as they act, and not as they have the power to act, as is said in the ninth book of Metaphysics (tex. 20 tr. 3). For any thing that comes under knowledge is being, is the true, in so far as it is in act, and this is manifestly apparent in sensible things. Thus the sight does not perceive that which may be colored, but that only which actually is colored. And in the same manner as is manifest, the intellect, in so far as it knows material things, knows that only which is in act.... Hence, also, in immaterial substances, each one is intelligible by its essence, accordingly as it is in act by its essence. Therefore, the essence of God, which is a pure and perfect act, is absolutely and perfectly intelligible by itself; thus God knows, by his essence, not only himself but also all other things. But the essence of the angel belongs to the class of intelligible beings as an act, but not as a pure and complete act, wherefore his understanding is not completed by his essence. For, although the angel knows himself by his essence, he cannot know all things by his essence, but knows those distinct from himself only by their images. But the human intellect in the class of intelligible beings is only a possible being.... Therefore, considered in its essence, it is an intelligent power; hence of itself it has the faculty of understanding, but not of being understood, except inasmuch as it acts. On this account the Platonists placed the order of intelligible beings above the order of intellect; because the intellect understands only by participation of the intelligible; but according to them, that which participates is beneath that of which it participates. If, then, the human intellect places itself in act by the participation of separate intelligible forms, as the Platonists held, it would know itself by this participation of incorporeal things. But as it is natural to our intellect in the present life to look to material and sensible things, it follows that our intellect knows itself only as it is placed in act by the species (ideas) abstracted from sensible things by the light of the intellect acting, which is the act of the intelligible things themselves.... Therefore our intellect does not know itself by its essence but by its acts."