The Affinity Argument

Socrates asks Cebes and Simmias to consider two kinds of reality. The first kind is visible, composite, changing, mortal — the things we perceive with our senses. The second kind is invisible, simple, unchanging, eternal — the Forms, which only thought can grasp. These are not the same kind of thing. They belong to different orders of being.

Now: which order does the body belong to? The visible, clearly — it is perceived by the senses, it is composite, it changes, it decays. And which order does the soul belong to? The soul, Socrates says, is most itself when it thinks — when it withdraws from the senses and engages with what is eternal. In that mode it resembles the eternal. Like keeps to like. The soul has more in common with the Forms than with the body, and so it belongs — in some deep sense — with the Forms.

When the body dies, the soul's fate depends on what it has been doing in life. The philosophical soul — the one that has spent its time thinking clearly, detaching from the body's demands — withdraws cleanly to the invisible realm. The unphilosophical soul, heavy with bodily attachments, wanders near the visible world it cannot quite leave. Socrates describes these fates in some detail, including the fate of the soul that loved its body so much that it haunts the graves of the living. The account is a myth, he says — but the general direction is what the argument establishes.