Commentaria in Summam contra Gentiles, Liber II

As to the third point, Saint Thomas sets forth certain arguments against a determinate truth ¹.

The first of these is as follows. The sensitive soul of man comes into being through the power of the seed, since it is of the same genus as the souls of the other animals. Therefore so too is the intellective soul. — The consequence is proved. Because in man the sensitive and the intellective are the same according to substance.

Second. The fetus is an animal before it is a man. Therefore it has a sensitive soul before it has an intellective one. But that soul is produced from seed. Therefore so is the intellective one, since the same soul becomes intellective, because an intellective soul that were another could not supervene upon it.

Third. The soul is united to the body with respect to esse. Therefore it is made by the same agent by which the body is made, since those things that are made one with respect to esse must terminate in a single action and a single agent. Therefore, etc.

Fourth. Man generates a being like himself in species by the power that is in the seed. Therefore he causes the soul, from which is man's species.

Fifth. According to Apollinaris, it would follow that God cooperates in adulteries: because, by creating the soul, He would give completion to an adulterous generation.

Sixth. Body and soul come into being simultaneously: otherwise the same thing would be prior and posterior to itself. Therefore, etc. — The consequence is evident. For the body begins to come into being at the emission of the seed.

Seventh. It would follow that God's action, and man's action, would be imperfect: because neither would produce the whole thing.

Eighth. The soul is a part of man. Therefore etc. — The consequence is proved. Because in all things generated from seed, all the parts of the thing generated are comprehended in the seed by virtue. This is illustrated in wheat, where the blade, stalk, internodes, fruit, and awns are comprehended in the first seed, and afterwards the seed is extended and dilated ² in order, by natural succession, toward the perfection of the thing, assuming nothing extrinsic: understand this as an efficient cause, although it may assume something extrinsic as matter.

Ninth. In the generation of man there is one and the same process of body and soul, and one and the same terminus: for according to the process of the formation and quantitative growth of the body, the operations of the soul are manifested more and more. Therefore etc.

Tenth. The body of man is formed by the action of the soul. First, because it is configured to itself. — Second, because the soul is the efficient cause of the body, as is said in II On the Soul, text 36. Therefore etc.

Eleventh. The seed lives, as appears from many considerations. Therefore there is in it a soul. Therefore, etc.

Twelfth. It follows that the body is first formed and the soul is afterward infused. Therefore the soul comes to be for the sake of the body: because what comes to be for the sake of something else is posterior to it, as is evident in garments, which are made for the sake of man.