summa-contra-gentiles

CHAPTER LXXXIII 247
Further. That which we acquire through the senses was
not in the soul before (its
union with) the body. Now,
knowledge of is principles caused in us from sensibles for
:
had we not perceived some whole by our senses, we should
be unable to understand that a whole is greater than its
part: just as a man born blind is unable to have an idea of
colours. Neither, therefore, had the soul any knowledge of
principles before (its union with) the body and much :
less,
of other things. Consequently Plato's proof of the existence
of the soul before its union with the body cannot stand.
Again.
If all souls existed before the bodies to which
they are united, it would seem to follow that the same soul
is united to different bodies according to the vicissitudes of
time. In fact this is an evident consequence of the opinion
of those who hold the eternity of the world. For,
if men
have been begotten from eternity,
it follows that an infinite
number of human bodies have been begotten and corrupted
during the whole course of time. Therefore we must say
either that an actually infinite number of souls pre-existed,
if each soul is united to a single body, or— if the number of
souls be finite— that the same soul is
united at one time to
this, at another time to that body. And the same would
seem to follow if we suppose that souls existed before
bodies, but that generation was not from eternity. For
although it be supposed that the begetting of men has not
always been, one cannot doubt that it can be of infinite
duration : because each man is so formed by nature, that
unless he be accidentally hindered, he is able to beget
another even as he himself was begotten of another. Yet
this is
impossible if, supposing a finite number of souls,
one soul cannot be united to several bodies. Wherefore
several who have asserted the existence of souls before
bodies, maintained the transmigration of souls. But this
is impossible. Therefore souls did not exist before bodies.
That one soul cannot possibly be united to different
bodies is
proved
thus. Human souls do not differ
specifically from one another, but only numerically
: else
men also would differ in species from one another. Now