Although I think that Plato introduces a profound connection in the Republic between harmony of soul and ethical disposition (justice is the peculiar excellence of the mind, injustice its defect), I do not think that his account of that harmony is successful. In the first place, Plato does not explain why anyone who enjoys harmony of soul should particularly want to act justly, except in the negative sense of not having insatiable appetites of a kind to make them ride roughshod over the interests of others. In the second place, what he presents as harmony is in reality an unstable inner conflict or tension, a tension which gives point to Nietzsche's accusation of ‘tyranny’. Socrates remains ‘a cave of every evil lust’ if we follow the anecdote about Zopyrus, but he is ‘master of them all’. This means he is really the victim of an inner division, he both rules himself and he rules the unwilling, an unresolved division of energies. I am not saying that we are not divided, nor that ethics doesn't require us to act sometimes against our inclinations. The point is we are being told a story about harmony that is not being delivered by the text.

On the other hand, something much closer to a genuine harmony with ethical implication, or rather, an ethics with implications for harmony, is found in the Symposium, in Diotima's description of the progressive states of eros, of the stages of the ascent to absolute beauty; in particular, in the implied idea of a decisive conative shift in the direction of someone's habitual attention and affective interest from physical beauty to ‘beauty of soul’.