Socrates initiates the conclusion of the dialogue by announcing that the rewards of justice are granted to the just after their mortal lives are over. Glaucon is surprised that Socrates holds with the immortality of the soul, but Socrates assures him that he, too, will agree once he hears Socrates' proof. And here is Socrates' proof:
There are all sorts of illnesses that can and do attack the body and bring about its demise. Every material thing we understand falls prey to its own unique "evil": wood rots; iron falls prey to rust; the body dies of the illnesses that attack it; and so on. But what is the "evil" peculiar to the soul? Of course, as we have seen, the soul's peculiar evil is injustice. But the souls of unjust men are not destroyed by injustice, and neither are the souls of just men. If a thing can be destroyed by its own particular evil (and only that), and if the soul cannot be destroyed by its own particular evil (injustice), then the soul must be immortal.
