Plato"s strategy in the republic is to first explain the primary notion of societal, or political, justice, and then to derive an equivalent concept of individual justice. In books ii, iii, and iv, plato identifies political justice as harmony in a structured political body. An ideal society consists of three main classes of people producers (craftsmen, farmers, artisans, etc. ), auxiliaries (warriors), and guardians (rulers); a society is just when relations between these three classes are right. Very important that these classes adhere to their functions: rulers must rule, auxiliaries must uphold rulers" convictions, and producers must limit themselves to exercising whatever skills nature granted them. What is justice in relation to the classes: justice is a principle of specialization: a principle that requires that each person fulfill the societal role to which nature fitted him and not interfere in any other business. At the end of book iv, plato tries to show that individual justice mirrors political justice.