 The discussion of the division of the soul sets the stage for Socrates’ final contrast of of justice with injustice: In the city there is justice if the members of the three classes mind their own business; in the individual soul, justice likewise consists in each part fulfilling its own function. This presupposes that the two upper parts have been given the right kind of training and education in order to control the appetitive part (441d–442a). The three other virtues are then assigned to the respective parts of the soul. Courage is the excellence of the spirited part, wisdom belongs to the rational part, and moderation is the consent of all three about who should rule and who should obey. Justice turns out to be the overall unifying quality of the soul (443c–e). For, the just person not only refrains from meddling with what is not his, externally, but also harmonizes the three parts of the soul internally. While justice is order and harmony, injustice is its opposite: it is a rebellion of one part of the city or soul against the others, and an inappropriate rule of the inferior parts. Justice and injustice in the soul are, then, analogous to health and illness in the body. This comparison suffices to bring the investigation to its desired result. If justice is health and harmony of the soul, then injustice must be disease and disorder. Hence, it is clear that justice is a good state of the soul that makes its possessor happy, and injustice is its opposite. Just as no-one in his right mind would prefer to live with a ruined body so no-one would prefer to live with a diseased soul. In principle, the discussion of justice has therefore reached its promised goal at the end of Book IV. Socrates has met Glaucon’s and Adeimantus’ challenge to prove that justice is a good, in and by itself, for the soul of its possessor, and preferable to injustice. 