Of God and His Creatures

It will be seen that the body of this argument, though not the conclusion, is the doctrine combatted by St Thomas above, "Nor again can it be said," etc., p. 175. St Thomas would not allow that the first sentient soul, which he supposes to be infused into man, the human foetus, and afterwards to perish, is "potentially intelligent." He holds that it does not turn into a rational soul, but simply ceases to be, when the rational soul comes in. "The intelligent soul which supervenes is another substance altogether" from the sentient soul in the mature and intelligent man (Chap. LVIII).

Of God and His Creatures: 2.88