Socrates determines that philosophers are best suited to the task. We are offered a vivid account of human psychology, about the motivations and outside forces that result in the degeneration of cities and souls, and we see the effects of that degeneration.
An apple is red and sweet, the theory goes, because it participates in the Forms of Redness and Sweetness. Book X Thereafter, Socrates returns to the subject of poetry and claims that the measures introduced to exclude imitative poetry from the just city seem clearly justified now a.
It begins with the dismissal of timocracy, a sort of authoritarian regime, not unlike a military dictatorship. It is here, after all, where we see Socrates's primary discussion of injustice, both in the city and the soul.
Socrates proceeds to discuss the education of philosopher kings c-d.
The first is whether the Republic is primarily about ethics or about politics.