Justice is thus a sort of harmony or balance of the mental powers; it is to the mind what health is to the body.

Health is the greatest good, sickness the greatest evil, of the body; so is Justice of the mind.
It is an essential of the Platonic Republic that, among the guardians at least, the sexual arrangements should be under public regulation, and the monopoly of one woman by one man forbidden: a regard to the breed of the higher caste of citizens requires the magistrate to see that the best couples are brought together, and to refuse to rear the inferior offspring of ill-assorted connexions.

The number of births is also to be regulated.
In carrying on war, special maxims of clemency are to be observed towards Hellenic enemies.
The education of the Guardians must be philosophical; it is for them to rise to the Idea of the good, to master the science of Good and Evil; they must be emancipated from the notion that Pleasure is the good.

To indicate the route to this attainment Plato gives his theory of cognition generally--the theory of Ideas;--and indicates (darkly) how these sublime generalities are to be reached.
The Ideal Commonwealth supposed established, is doomed to degradation and decay; passing through Timocracy, Oligarchy, Democracy, to Despotism, with a corresponding declension of happiness.

The same varieties may be traced in the Individual; the 'despotized' mind is the acme of Injustice and consequent misery.
The comparative value of Pleasures is discussed.