Then a further step in advance was made, and some surmised the existence of something incorporeal, not apart from the body, but the form of a body; so that Varro said, "God is a soul governing the world by movement and reason," as Augustine relates (De Civ. Dei vii, 6 [*The words as quoted are to be found iv. 31.]). So some supposed man's soul to be part of that one soul, as man is a part of the whole world; for they were unable to go so far as to understand the different degrees of spiritual substance, except according to the distinction of bodies.
But, all these theories are impossible, as proved above (Q. 3, AA. 1, 8; and Q. 75, A. 1), wherefore it is evidently false that the soul is of the substance of God.
Reply Obj. 1: The term "breathe" is not to be taken in the material sense; but as regards the act of God, to breathe (spirare), is the same as to make a spirit. Moreover, in the material sense, man by breathing does not send forth anything of his own substance, but an extraneous thing.
Reply Obj. 2: Although the soul is a simple form in its essence, yet it is not its own existence, but is a being by participation, as above explained (Q. 75, A. 5, ad 4). Therefore it is not a pure act like God.
Reply Obj. 3: That which differs, properly speaking, differs in something; wherefore we seek for difference where we find also resemblance. For this reason things which differ must in some way be compound; since they differ in something, and in something resemble each other. In this sense, although all that differ are diverse, yet all things that are diverse do not differ. For simple things are diverse; yet do not differ from one another by differences which enter into their composition. For instance, a man and a horse differ by the difference of rational and irrational; but we cannot say that these again differ by some further difference. _______________________
SECOND ARTICLE [I, Q. 90, Art. 2]
Whether the Soul Was Produced by Creation?
Objection 1: It would seem that the soul was not produced by creation. For that which has in itself something material is produced from matter. But the soul is in part material, since it is not a pure act. Therefore the soul was made of matter; and hence it was not created.
Obj. 2: Further, every actuality of matter is educed from the potentiality of that matter; for since matter is in potentiality to act, any act pre-exists in matter potentially. But the soul is the act of corporeal matter, as is clear from its definition. Therefore the soul is educed from the potentiality of matter.
Obj. 3: Further, the soul is a form. Therefore, if the soul is created, all other forms also are created. Thus no forms would come into existence by generation; which is not true.