... what is that the inherence of which, will render the body alive? [The soul.]... Then whatever the soul possesses, to that she comes bearing life?... And is there an opposite to life? [Death.] Then the soul, as she has been acknowledged, will never receive the opposite of what she brings.... And what do we call the principle which does not admit of death? [The immortal.] And does the soul admit of death? [No.] Then the soul is immortal? [Yes.]

Plato - Phaedo