Plato developed his moral and metaphysical theory most fully in the Republic. In the dialogue Plato attempted to determine whether it is in one's own best interests to be a just person. He addressed the commonly assumed idea that injustice pays if one can get away with it and that just behavior merely serves the interests of others. Plato attempted to show that on the contrary justice when properly understood is so great a good that it is worthy any sacrifice.
To support this thesis Plato portrayed the ideal political community. He argued that an ideal city must make radical innovations. It should be ruled by specially trained philosophers. These are the elite of the community. Plato compared their education to the experience of the individual coming out of a darkened cave and suddenly being exposed to the light of the sun. Thereafter they are equipped to return to the dark of the cave and to see the images in the cave for exactly what they are . . . nothing more than images.
Everything in the ruler's lives is designed, according to Plato, to shape their allegiance to the community. Private possessions are disallowed. Their sexual lives are regulated by eugenic considerations. They are not to know who their children are. Philosophical reflection is the primary directive for moral education.
The society consists of three categories. The philosopher rulers are ideally equipped to rule. The soldiers are charged with the responsibility of enforcing the commands of the rulers. The economic class is composed of farmers, craftsmen, builders and other common laborer and is to leave the task of making and enforcing the laws to the previously mentioned classes.
Plato compared the perfect community to the elements composing human nature. The part of the individual that is capable of reason and rationality is to rule. The part of the individual that is assertive and capable of anger and competitive is charged with the responsibility of provides the force required by understanding. The part of the individual that consists of the drives for food and sex is to be trained to pursue only those things that the intellect approves. So is reflected the structure of the perfect community in the make up of each individual.
Plato's Republic centers on a simple question: Is it always better to be just than unjust?
