If you read The Republic, Socrates sounds like he’s just saying stuff with no proof and little evidence. The uninitiated must wonder: why should we take him so seriously? Plato’s argument for the three parts of the soul is absurd. He does not “arrive logically” at the three parts of the soul.
But maybe this is because he is not trying to prove that there are three parts of the soul. Maybe he already knows that there’s three parts of the soul. Maybe he came to this knowing through some super-rational, super-sensible method. Maybe in deep-contemplation or a mystery ritual. Or maybe her learned about them through Pythagoras, who learned them from India. The three parts of the soul in Plato’s Republic correspond perfectly to the three gunas in the Bhagavad Gita. And over time, these concepts turned into living truths in him.
And so maybe the purpose of Plato’s dialogues is to build proofs by logically reasoning from sense-perceptible life, as Aristotle does. But to convey mystical insight in an argumentative way.