The Republic, philosophical work written by Plato in the form of a dialogue, an inquiry into the nature of justice and the organization of a perfect society. The work is a lengthy exposition of the ideas underlying Plato's earlier dialogues and is an attempt to unite rational, ethical, and religious principles.

According to Socrates, the principal speaker in The Republic, an ideal state would consist of three classes. The philosopher-kings would exercise political power in the service of justice and wisdom; the soldiers would protect the state as a means of acquiring honour; and the civilian population would provide for the material needs of society. A large part of The Republic is devoted to a detailed presentation of the rigorous intellectual training of future rulers. This section also contains a fundamental analysis of metaphysical and scientific thought. The government of the state acts to enforce the virtue, and consequently the true happiness, of the individual citizen, and an orderly and productive public life is the result. Criticizing the doctrines of atheism and materialism, Plato reaffirmed his idealistic position and asserted his belief in the moral government of the universe and the immortality of the soul.