ve (Q. 115, A. 3, ad 2). And since in this
(vital) spirit the power of the soul is concurrent with the power of
a heavenly body, it has been said that "man and the sun generate
man." Moreover, elemental heat is employed instrumentally by the
soul's power, as also by the nutritive power, as stated (De Anima ii,
4).

Reply Obj. 4: In perfect animals, generated by coition, the active
force is in the semen of the male, as the Philosopher says (De Gener.
Animal. ii, 3); but the foetal matter is provided by the female. In
this matter, the vegetative soul exists from the very beginning, not
as to the second act, but as to the first act, as the sensitive soul
is in one who sleeps. But as soon as it begins to attract
nourishment, then it already operates in act. This matter therefore
is transmuted by the power which is in the semen of the male, until
it is actually informed by the sensitive soul; not as though the
force itself which was in the semen becomes the sensitive soul; for
thus, indeed, the generator and generated would be identical;
moreover, this would be more like nourishment and growth than
generation, as the Philosopher says. And after the sensitive soul, by
the power of the active principle in the semen, has been produced in
one of the principal parts of the thing generated, then it is that
the sensitive soul of the offspring begins to work towards the
perfection of its own body, by nourishment and growth. As to the
active power which was in the semen, it ceases to exist, when the
semen is dissolved and the (vital) spirit thereof vanishes. Nor is
there anything unreasonable in this, because this force is not the
principal but the instrumental agent; and the movement of an
instrument ceases when once the effect has been produced.
_______________________

SECOND ARTICLE [I, Q. 118, Art. 2]

Whether the Intellectual Soul Is Produced from the Semen?

Objection 1: It would seem that the intellectual soul is produced
from the semen. For it is written (Gen. 46:26): "All the souls that
came out of [Jacob's] thigh, sixty-six." But nothing is produced from
the thigh of a man, except from the semen. Therefore the intellectual
soul is produced from the semen.

Obj. 2: Further, as shown above (Q. 76, A. 3), the intellectual,
sensitive, and nutritive souls are, in substance, one soul in man.
But the sensitive soul in man is generated from the semen, as in
other animals; wherefore the Philosopher says (De Gener. Animal. ii