 That resolution rests on the division of the soul into three parts by which the Republic places moral psychology at the heart of political philosophy. Both soul and city are posited by Socrates in arguments in Books II–IV and VIII–IX, in particular, to have a tripartite structure when the soul is embodied in a living person. In the soul and city respectively, the rational part or class should rule; the spirited part or class should act to support the rule of that rational part; and the appetitive part of the soul and producing class in the city should accept being governed by it. Both soul and city are therefore in need of, and capable of exhibiting, four virtues (427e–444a). Two of these pertain to individual parts: the rational part being capable of wisdom, the spirited part of courage. Two however are defined by relations between the parts: moderation as the agreement of all three parts that reason should rule, justice as each part doing its own (this echoes, in a radically new context, a conservative Athenian suspicion of excessive democratic polupragmosunê or busybody interference).