Of God and His Creatures

The body being the principle of individuation, when that principle is taken away, it would seem that nothing is left to differentiate one soul from another. St Thomas would reply that the soul is individualised, not by the body, but by adaptation to one particular body which it animates and informs, which adaptation continues after that body is dead and gone. See Chap. LXXV, arg. 1, with reply and note; and in this chapter the reply to the second argument.

Of God and His Creatures: 2.80