 Given the complexity of the differences among the parts, we can now understand how their relations to one another define virtue in the soul. Virtue reduces the potential for conflict to harmony. The master virtue, justice, is each part doing its function and not interfering with that of another (441d–e; 443d). Since the function of reason is to exercise forethought for the whole soul, it should rule. The appetites, which seek only their immediate satisfaction, should not rule. A soul ruled by appetites is the very picture of psychological injustice. Still, to fulfill its function of ruling, reason needs wisdom, the knowledge of what is beneficial for each of the parts of the soul and for the whole. Moderation is a harmony among the parts based on agreement that reason should rule. Courage is the spirited part carrying out the decrees of reason about what is to be feared (442b–d). Any attentive reader of the dialogues must feel that Socrates has now given an answer to the questions that started many of the aporetic dialogues. At this point, we have the fully developed moral psychology that allows the definition of the moral virtues. They fall into place around the tripartite structure of the soul.