3. Everything out of which anything is made is in potentiality to that which is made out of it. But the substance of God, being pure actuality, is not in potentiality to anything (B. I, Chap. XVI).
4 and 5. That out of which anything is made is in some way changed. Moveover the soul of man is manifestly variable in point of knowledge, virtue, and their opposites. But God is absolutely unchangeable (B. I, Chap. XII): therefore nothing can be made out of Him, nor can the soul be of His substance.
7. Since the divine substance is absolutely indivisible, the soul cannot be of that substance unless it be the whole substance. But the divine substance cannot but be one (B. I, Chap. XLII). It would follow that all men have but one intellectual soul, a conclusion already rejected (Chap. LXXV).*
This opinion seems to have had three sources. Some assumed that there was no incorporeal being, and made the chiefest of corporeal substances God. Hence sprang the theory of the Manichean, that God is a sort of corporeal light, pervading all the infinities of space, and that the human soul is a small glimmer of this light. Others have posited the intellect of all men to be one, either active intellect alone, or active and potential combined. And because the ancients called every self-subsistent intelligence a deity, it followed that our soul, or the intellect whereby we understand, had a divine nature. Hence sundry professors of the Christian faith in our time, who assert the separate existence of the active intellect, have said expressly that the active intellect is God. This opinion might also have arisen from the likeness of our soul to God: for intelligence, which is taken to be the chief characteristic of Deity, is found to belong to no substance in the sublunary world except to man alone, on account of his soul.
2.83, 84 : Apparent Arguments to show that the Human Soul does not begin with the Body, but has been from Eternity, with Replies to the same
2.86 : That the Human Soul is not transmitted by Generation