The Platonic dialogue with the disjunctive title "Republic or On Justice" is one of the finest works from the peak period of the author. In the first book, there is a dialogue about Justice, and in the second, the discussion focuses on what is just, referencing the myth of Gyges.

The dialogue in the third book refers to the education of the guardians and what should govern them. The physical training should aim at perfecting the inherent qualities that the guardians possess (speed, alertness, endurance), and the diet should be simple and frugal.

Continuing into the fourth book, a dialogue takes place about how a city of justice should function. The preservation of political justice is a task that the class of rulers must take care of. The three classes of the city correspond to the individual soul, namely: rulers= rational, guardians= spirited, artisans= appetitive.