The polis, or Greek city-state, according to Aristotle, is the highest form of political association. Only by being a citizen of a polis can a person fully pursue a life of good quality, which is the end goal of human existence. Because one can only achieve this goal through political association, Aristotle concludes that "man is a political animal." As well as defending private property and condemning capitalism, Aristotle notoriously regards the institution of slavery as necessary to the workings of society.
Reviewing and criticizing other constitutions and constitutional theories, Aristotle concludes that no present city or theory is ideal. He identifies cities with their respective constitutions and categorizes six different kinds of cities, three good and three bad. The three good kinds are politeia, or constitutional government; aristocracy; and kingship. The three bad kinds are democracy, oligarchy, and tyranny. A good constitution is formulated according to the principle of distributive justice: equal people are treated equally and unequal people are treated unequally. People are deemed more or less valuable to society according to the contributions they make to the life of the city. Though Aristotle states that a constitutional government with a sovereign set of laws is ideal, he admits that in cases where there is an outstanding group or individual, aristocracy or kingship might be preferable.
Books IV–VI turn away from the abstract questions of political theory and examine practical questions related to the political structure of the ancient Greece in which Aristotle lived. Aristotle reviews the many different manifestations of the different forms of government and remarks on the value of a strong middle class that can mediate between the opposing interests of the rich and the poor.
The government of cities is generally divided between deliberative, judicial, and executive functions, and Aristotle discusses the different ways in which these functions can be fulfilled. Regardless of who is in power, it is prudent never to exclude completely those who are not in power. Moderation, education, and respect for all will ensure stability. Constitutions change when a large faction opposed to the present government arises and institutes a different conception of justice and equality.
Envisioning an ideal city, Aristotle states that the goal of the city is to help each citizen achieve happiness, which is found in the free exercise of speculative reasoning. All other goods are just means to this end. Aristotle recommends keeping the city small, but large enough to be self-sufficient. The citizens should all share in military service, government, religious service, and land ownership, but they should leave crafts and food production to non- citizen laborers. In terms of education, Aristotle recommends a program of reading and writing, drawing, physical training, and music. This education should be directed toward the end of achieving a life of good quality, and should encourage life skills, moral goodness, and cultivation of the mind.