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(5) Is there in them any other power of knowledge besides the intellect?
FIRST ARTICLE [I, Q. 54, Art. 1]
Whether an Angel's Act of Understanding Is His Substance?
Objection 1: It would seem that the angel's act of understanding is his substance. For the angel is both higher and simpler than the active intellect of a soul. But the substance of the active intellect is its own action; as is evident from Aristotle (De Anima iii) and from his Commentator [*Averroes, A.D. 1126-1198]. Therefore much more is the angel's substance his action--that is, his act of understanding.
Obj. 2: Further, the Philosopher says (Metaph. xii, text 39) that "the action of the intellect is life." But "since in living things to live is to be," as he says (De Anima ii, text 37), it seems that life is essence. Therefore the action of the intellect is the essence of an angel who understands.
Obj. 3: Further, if the extremes be one, then the middle does not differ from them; because extreme is farther from extreme than the middle is. But in an angel the intellect and the object understood are the same, at least in so far as he understands his own essence. Therefore the act of understanding, which is between the intellect and the thing understood, is one with the substance of the angel who understands.
_On the contrary,_ The action of anything differs more from its substance than does its existence. But no creature's existence is its substance, for this belongs to God only, as is evident from what was said above (Q. 3, A. 4). Therefore neither the action of an angel, nor of any other creature, is its substance.
_I answer that,_ It is impossible for the action of an angel, or of any creature, to be its own substance. For an action is properly the actuality of a power; just as existence is the actuality of a substance or of an