Reason and the Good in Plato’s Republic

Let me begin with some of the background worries that motivate the paper. First, for years I have been working on the relation of the Timaeus to the Republic guided by this triple analogy: as the demiurge is to the cosmos, so the philosopher-ruler is to the polis, so reason is to the soul or individual. The key claim is Tim. 29e: the demiurge is good and so wants to make everything it makes like it itself is, i.e., good, as good as possible. I take the demiurge to be reason idealized, so I infer reason wants to make everything it makes as good as possible. This sets the stage: how is reason related to the good?