 The promise to establish the isomorphic structure of the city and soul has not been forgotten. After the definition and assignment of the four virtues to the three classes of the city, the investigation turns to the role and function of the virtues in the soul. The soul is held to consist of three parts , corresponding to the three classes in the city. The lengthy argument for the tri-partition of the soul into a rational (logistikon), a spirited (thumoeides), and an appetitive (epithumêtikon) part (434d–441c), can here be neither reproduced nor subjected to critical evaluation. That Plato lets Socrates express reservations concerning the adequacy of his own procedure (435c–d), despite his unusually circumspect way of justifying his division of the soul’s faculties, indicates that he regards it as an important innovation. Indeed, there is no indication of separate parts of the soul in any of the earlier dialogues; irrational desires are attributed to the influence of the body. In the Republic, by contrast, the soul itself becomes the source of the appetites and desires. The difference between the rational and the appetitive part is easily justified, because the opposition between the decrees of reason and the various kinds of unreasonable desires is familiar to everyone (438d–439e). The existence of a third, a ‘spirited’ or courageous part – different from reason and desire – is harder to prove. But the phenomenon of moral indignation is treated as evidence for a psychic force that is reducible neither to reason nor to any of the appetites; it is rather an ally of reason in a well-ordered soul, a force opposed to unruly appetites (439e–441c). This concludes the proof that there are three parts in the soul corresponding to the three classes in the city – namely the rational part in the wisdom of the rulers, the spirited part, which is manifested in the courage of the soldiers, the appetitive part, which is manifested in the rest of the population, whose defining motivation is material gain. 