Comparing Plato and Aristotle on government and the concept of good.

Plato is primarily concerned with knowing the good. In the Republic, Plato intends to define justice and describes an elaborate city-state setup with the goal of being a just city. A guardian class of philosophers rules in Plato's city, because these are the only people who can know the good. Everyone else's role in the city is to do their work to support the city so that the guardians are able to philosophize. Aristotle does …

…only philosophers can know the good. Frankly, Plato does not care about the average person because he cannot know the good. Conversely, Aristotle is concerned about the well being of all people, and he wants them to be good throughout their lives. His government reflects this as Aristotle seeks to provide laws that are just and in everyone's interest. For Aristotle, it does not matter that people know the good, but that they live good.