The Unity of the Virtues and the Degeneration of Kallipolis

Each of the degenerating constitutions in Book VIII of Plato's Republic is the result of the disappearance of one of the four cardinal virtues. The failure of wisdom creates a timocracy; the failure of courage, an oligarchy; the failure of moderation, a democracy; the failure of justice, a tyranny. The degeneration shows that the disunited virtues are imperfect, though they have some power to stave off vice. Thus Book VIII implies a unity of the virtues thesis according to which perfect virtues can only exist in a united state, but imperfect simulacra of virtue can exist in a disunited state.