Summa Theologica, Part I (Prima Pars) From the Complete...

Objection 1: It would seem that the soul was not made, but was God's substance. For it is written (Gen. 2:7): "God formed man of the slime of the earth, and breathed into his face the breath of life, and man was made a living soul." But he who breathes sends forth something of himself. Therefore the soul, whereby man lives, is of the Divine substance.

Obj. 3: Further, things that exist and do [not] differ are the same. But God and the mind exist, and in no way differ, for they could only be differentiated by certain differences, and thus would be composite. Therefore God and the human mind are the same.

On the contrary, Augustine (De Orig. Animae iii, 15) mentions certain opinions which he calls "exceedingly and evidently perverse, and contrary to the Catholic Faith," among which the first is the opinion that "God made the soul not out of nothing, but from Himself."

I answer that, To say that the soul is of the Divine substance involves a manifest improbability. For, as is clear from what has been said (Q. 77, A. 2; Q. 79, A. 2; Q. 84, A. 6), the human soul is sometimes in a state of potentiality to the act of intelligence —acquires its knowledge somehow from things—and thus has various powers; all of which are incompatible with the Divine Nature, Which is a pure act—receives nothing from any other—and admits of no variety in itself, as we have proved (Q. 3, AA. 1, 7; Q. 9, A. 1).

This error seems to have originated from two statements of the ancients. For those who first began to observe the nature of things, being unable to rise above their imagination, supposed that nothing but bodies existed. Therefore they said that God was a body, which they considered to be the principle of other bodies. And since they held that the soul was of the same nature as that body which they regarded as the first principle, as is stated De Anima i, 2, it followed that the soul was of the nature of God Himself. According to this supposition, also, the Manichaeans, thinking that God was corporeal light, held that the soul was part of that light bound up with the body.

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.

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. 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. _______________________

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.

I answer that, The rational soul can be made only by creation; which, however, is not true of other forms. The reason is because, since to be made is the way to existence, a thing must be made in such a way as is suitable to its mode of existence. Now that properly exists which itself has existence; as it were, subsisting in its own existence. Wherefore only substances are properly and truly called beings; whereas an accident has not existence, but something is (modified) by it, and so far is it called a being; for instance, whiteness is called a being, because by it something is white. Hence it is said Metaph. vii, Did. vi, 1 that an accident should be described as "of something rather than as something." The same is to be said of all non-subsistent forms. Therefore, properly speaking, it does not belong to any non-existing form to be made; but such are said to be made through the composite substances being made. On the other hand, the rational soul is a subsistent form, as above explained (Q. 75, A. 2). Wherefore it is competent to be and to be made. And since it cannot be made of pre-existing matter—whether corporeal, which would render it a corporeal being—or spiritual, which would involve the transmutation of one spiritual substance into another, we must conclude that it cannot exist except by creation.

Reply Obj. 1: The soul's simple essence is as the material element, while its participated existence is its formal element; which participated existence necessarily co-exists with the soul's essence, because existence naturally follows the form. The same reason holds if the soul is supposed to be composed of some spiritual matter, as some maintain; because the said matter is not in potentiality to another form, as neither is the matter of a celestial body; otherwise the soul would be corruptible. Wherefore the soul cannot in any way be made of pre-existent matter.

Reply Obj. 2: The production of act from the potentiality of matter is nothing else but something becoming actually that previously was in potentiality. But since the rational soul does not depend in its existence on corporeal matter, and is subsistent, and exceeds the capacity of corporeal matter, as we have seen (Q. 75, A. 2), it is not educed from the potentiality of matter.