2. If the human soul owed its origin to the transmission of the male semen, that could be only in one of two ways. Either we must suppose that the soul is actually in the male semen, being as it were accidentally separated from the soul of the generator as the semen is separated from the body: -- we see something of this sort in Annelid animals,* that live when cut in pieces: these creatures have one soul actually and many potentially; and when the body is divided, a soul comes to be actually in every living part: -- or in another way it may be supposed that there is in the male semen a power productive of an intellectual soul, so that the intellectual soul may be taken to be in the said semen virtually, not actually. The first of these suppositions is impossible for two reasons. First, because the intelligent soul being the most perfect of souls and the most potent, the proper subject for it to perfect is a body having a great diversity of organs apt to respond to its manifold activities: hence the intellectual soul cannot be in the male semen cut off from the body (in semine deciso), because neither are the souls of the lower animals of the more perfect sort multiplied by cutting them in pieces (per decisionem), as is the case with Annelid animals. Secondly, because the proper and principal faculty of the intelligent soul, the intellect, not being the actualisation of any part of the body,* cannot be accidentally divided with the division of the body: therefore neither can the intelligent soul. The second supposition (that the intelligent soul is virtually contained in the male semen) is also impossible. For the active power in the semen is effectual to the generation of an animal by effecting a bodily transmutation: there is no other way for a material power to take effect. But every form, which owes its being to a transmutation of matter, has being in dependence on matter: for (n. 3) every form, educed into existence by a transmutation of matter, is a form educed out of the potentiality of matter: for this is the meaning of a transmutation of matter, that something is educed into actuality out of potentiality. But an intelligent soul cannot be educed out of the potentiality of matter: for it has been shown above (Chap. LXVIII) that the intelligent soul transcends the whole power of matter, as it has an immaterial activity (Chap. LXIX). Therefore the intelligent soul is not induced into being by any transmutation of matter, and therefore not by the action of any power that is in the male semen.
5. It is ridiculous to say that any subsistent intelligence is either divided by division of the body or produced by any corporeal power. But the soul is a subsistent intelligence (Chap. LXVIII). Therefore it can neither be divided by the separation of the semen from the body, nor produced by any active power in the same.
6. If the generation of this is the cause of that coming to be, the destruction of this will be the cause of that ceasing to be. But the destruction of the body is not the cause of the human soul ceasing to be (Chap. LXXIX). Neither then is the generation of the body the cause of the soul commencing to be.
2.85 : That the Soul is not of the Substance of God
2.87 : That the Human Soul is brought into being by a Creative Act of God