The Final Argument

Socrates begins with Simmias's harmony objection. He points out a fatal flaw: harmonies admit of degrees. A lyre can be more or less in tune, more or less a harmony. But we already agreed that no soul is more or less a soul than another. Every soul is equally and completely a soul. The harmony analogy therefore breaks down at this point — the analogy's central property doesn't apply to the thing it's supposed to describe. He adds a further problem: the soul commands the body, rules its pleasures and pains, acts against the harmony of the body when virtue requires. A harmony cannot contradict its instrument.

He then turns to Cebes's objection and builds the final argument. There is a crucial distinction between an opposite and the thing that brings an opposite. Snow is not cold itself — it brings cold. Fire is not heat itself — it brings heat. When the cold approaches snow, the snow does not become cold — it withdraws or perishes. When heat approaches fire, the fire does not become cold — it retreats or is extinguished. Things that bring a property cannot admit the opposite of that property while remaining what they are.

Now apply this to the soul. The soul is what brings life — wherever the soul is present, life is present. What brings life cannot admit death. When death approaches, the soul must either withdraw or perish. But Socrates argues it cannot perish — that would be to admit its opposite, which the preceding argument has ruled out. The soul is immortal. Cebes and Simmias are convinced. Socrates then tells the myth of the afterlife — the true shape of the earth, the fate of different kinds of souls, the places of punishment and purification — as a likely story, not a certain one. But the direction the argument has established, he says, is where the myth points.