Because his unawareness of the difference between people, Plato automatically assumes that individual soul shares the same three elements with society as a whole which are, ration, reason and appetite. As a result, Plato concludes there is no difference between a just man and a just society, when it comes to searching justice for individuals in the state. Moreover, Plato argues that state is formed for particular purpose. Individual people are not self-sufficient and no one can acquire all the necessities in life. In order to resolve this difficulty, we gather together in order to achieve our common goals. In order to keep the state well functioning, we need people with different professions to work together for common interest. Therefore, not only labors are specialized but also guardians. The Guardians are the rulers that make sure the entire state will be well governed. Therefore, the other people need to follow the guardians in order to keep the state well functioned. In other words, Plato thinks unity of the state is the key to keep most people happy. If everyone plays their own role well, the state will prosper and everyone will be happy.
In contrast to Plato, Aristotle was not that interested in seeking absolute truth. Rather than that, Aristotle favors an ideal that is more practical and real at his time and his place. Therefore, unlike Plato, Aristotle sees state as a nature community. He agrees with Plato that men cannot live without a society, but he thinks state is "the nature and final growth of human relations." (Ebenstein, P76) In other words, state was not created for any purpose or to serve anyone. To Aristotle, all associations are political, but the state aims to the highest good in the society. However, Aristotle does not emphasize state unity much as Plato does. First, Aristotle focus more on the highest purpose of the state, instead of the highest authority of the state.