Come up with me to the hill which overhangs the city and look down upon the single form of virtue, and the infinite forms of vice, among which are four special ones, characteristic both of states and of individuals.

And the state which corresponds to the single form of virtue is that which we have been describing, wherein reason rules under one of two names--monarchy and aristocracy.

Thus there are five forms in all, both of states and of souls...
In attempting to prove that the soul has three separate faculties, Plato takes occasion to discuss what makes difference of faculties.

And the criterion which he proposes is difference in the working of the faculties.

The same faculty cannot produce contradictory effects.