Just as political justice consists in the structural relations among classes of society, Plato believes, individual justice consists in correct structural relations among parts of the soul. Paralleling the producers, warriors, and rulers in the city, Plato claims that each individual soul has three separate seats of desire and motivation:

1) The appetitive part of our soul lusts after food, drink, sex, and so on (and after money most of all, since money is the means of satisfying the rest of these desires);

2) The spirited part of the soul yearns for honor; and

3) The rational part of the soul desires truth and knowledge.

In a just soul, these three parts stand in the correct power relations. The rational part must rule, the spirited part must enforce the rational part’s convictions, and the appetitive part must obey. In the just soul, the desires of the rational, truth-loving part dictate the overall aims of the human being. All appetites and considerations of honor are put at the disposal of truth-loving goals. The just soul strives wholly toward truth. Plato identifies the philosopher (literally “truth lover”) as the most just individual, and sets him up as ruler of the just city.