In the Republic, Plato’s theory of forms reaches its full development as he presents a (to him) utopian way of life. In order to understand justice in the individual, he sets out to describe a just city (the individual “writ large”). The main political principle of justice is a kind of division of labor that is mirrored in the tri-part division of the human being, or soul, into body, emotions and spirit, and reason. (For Plato, what we experience as the body belonged to the realm of mere appearance.) Just as human beings are happiest when their reason rules, it is necessary that the ideal city be ruled by those in whom reason is most perfect: namely, philosopher kings and queens.