The Three Castes of the State

When he gets to design his ideal state, Plato has three classes of people. He divides up the state into these three categories - artisans, farmers and philosophers. The danger is that once you have guards, they could also become like wolves upon these sheep. So what you then need is a third group who would have to be philosophers. These philosophers would love reason and truth so much that they wouldn't have any private self-interest which they were trying to pursue in ruling. And ironically, they are the people who least want to rule, and therefore they are best suited to rule.