We next consider the production of man from man: first, as to the soul; secondly, as to the body.
Under the first head there are three points of inquiry:
(1) Whether the sensitive soul is transmitted with the semen?
(2) Whether the intellectual soul is thus transmitted?
(3) Whether all souls were created at the same time? _______________________
FIRST ARTICLE [I, Q. 118, Art. 1]
Whether the Sensitive Soul Is Transmitted with the Semen?
Objection 1: It would seem that the sensitive soul is not transmitted with the semen, but created by God. For every perfect substance, not composed of matter and form, that begins to exist, acquires existence not by generation, but by creation: for nothing is generated save from matter. But the sensitive soul is a perfect substance, otherwise it could not move the body; and since it is the form of a body, it is not composed of matter and form. Therefore it begins to exist not by generation but by creation.
Obj. 2: Further, in living things the principle of generation is the generating power; which, since it is one of the powers of the vegetative soul, is of a lower order than the sensitive soul. Now nothing acts beyond its species. Therefore the sensitive soul cannot be caused by the animal's generating power.
Obj. 3: Further, the generator begets its like: so that the form of the generator must be actually in the cause of generation. But neither the sensitive soul itself nor any part thereof is actually in the semen, for no part of the sensitive soul is elsewhere than in some part of the body; while in the semen there is not even a particle of the body, because there is not a particle of the body which is not made from the semen and by the power thereof. Therefore the sensitive soul is not produced through the semen.