Summa contra Gentiles2.86 Chapter LXXXVI. That the human soul is not transmitted with the semen

It may be shown from the foregoing that the human soul is not transmitted with the semen, as though it were sown by coition.

For any principles whatsoever that cannot exercise their operations without the body cannot begin to exist apart from the body: because a thing’s being is proportionate to its operation, since everything operates according as it is a being. On the other hand, those principles which exercise their operations without the body, are generated apart from the generation of the body. Now the operation of the nutritive and sensitive soul cannot be without the body, as is evident from what has been said: whereas the operation of the intellective soul is not exercised through an organ of the body, as stated above. Consequently the nutritive and sensitive souls are generated through the generation of the body; but not the intellective soul. Now the transmission of the semen is directed to the generation of the body. Therefore the nutritive and sensitive souls begin to exist through the transmission of the semen; but not the intellective soul.

Again. If the human soul began to exist by transmission with the semen, this could only be in two ways. In one way, so that we understand it to be in the semen actually, as though it were accidentally severed from the soul of the generator, just as the semen is severed from the body. This may be seen in annulose animals, that live after being cut in two, and in which there is one soul actually and several in potentiality: for when the body of such an animal is divided, the soul begins to be actually in each living part. In another way, so that we understand the semen to possess a virtue productive of the intellective soul: and thus the intellective soul would be in the semen virtually, but not actually.

But the former of these is impossible for two reasons. First, because, since the intellective soul is the most perfect of souls and endowed with the highest power, its proper matter is a body having a great variety of organs, whereby its manifold operations can be accomplished. Consequently it cannot possibly be actually in the separated semen; since not even the souls of perfect irrational animals are multiplied by division as happens in annulose animals. Secondly, because, since the intellect, which is the proper and principal power of the intellective soul, is not the act of any part of the body, it cannot be accidentally divided through the body being divided: and consequently neither can the intellective soul.

The second is also impossible. For the active force in the semen promotes the generation of the animal by transmuting the body: because a material force cannot act otherwise. Now every form that begins to exist through the transmutation of matter, has a being dependent on matter: because the transmutation of matter reduces it from potentiality to act, and thus terminates in the actual being of matter, which results from its union with a form; wherefore, if thereby the being of the form also begins simply, the being of the form will consist merely in its being united to matter, and consequently the form will be dependent on matter for its being. Therefore, if the human soul is brought into being by an active force in the semen, it follows that its being is dependent on matter, like the being of other material forms: whereas the contrary of this has been proved above. Therefore the intellective soul is nowise brought into being through the transmission of the semen.

Moreover. Every form that is brought into being through the transmutation of matter, is brought forth from the potentiality of matter: since the transmutation of matter is its reduction from potentiality to act. Now the intellective soul cannot be brought forth from the potentiality of matter: for it has been shown above that the intellective soul surpasses the whole potentiality of matter, since it has an operation apart from matter, as was proved above. Therefore the intellective soul is not brought forth into being through the transmutation of matter; and neither, consequently, by the action of a power residing in the semen.

Further. No active force acts beyond its genus. But the intellective soul surpasses the whole genus of bodies: since it has an operation that is raised above all bodies, namely intelligence. Therefore no bodily force can produce an intellective soul. Now whatever action proceeds from a force that is in the semen, results from a bodily force; because the formative force acts through the medium of the threefold heat, of fire, of heaven, and of the soul. Therefore the intellective soul cannot be brought into being by a force residing in the semen.

Further. It is absurd to state that an intellective substance is either divided through a body being divided, or produced by a bodily virtue. Now the human soul is an intellective substance, as we proved above. Therefore it cannot be said that it is divided through the semen being divided, or that it is brought into being by an active virtue in the semen. Consequently the human soul nowise begins to exist through the transmission of the semen.

Further. If the generation of a thing causes a certain thing to exist, the corruption of the former will cause the latter to cease to exist. Now the corruption of the body does not cause the soul to cease to exist, for the latter is immortal, as we have proved above. Neither, therefore, is the generation of the body the cause of the soul beginning to exist. But the transmission of the semen is the proper cause of the generation of the body. Therefore the transmission of the semen is not the cause of the soul being brought into existence.

Hereby is excluded the error of Apollinaris and his followers who said that souls are generated hy souls, as bodies by bodies.