Plato's Theory of Desire

My aim here is to make sense of Plato's account of desire in the middle dialogues. To do that I need to unify or reconcile what are at first sight two quite different accounts: the doctrine of eros in the Symposium and the tripartite theory of motivation in the Republic. It may be that the two theories are after all irreconcilable, that Plato simply changed his mind on the nature of human desire after writing the Symposium and before composing the Republic. But that conclusion can be justified only if attempts to reconcile the two theories end in failure. The attempt must be made first.