Aristotle discusses different forms of government in his book Politics. He identifies three main forms - monarchy, aristocracy, and constitutional government. For each form there is a perversion - tyranny, oligarchy, and democracy respectively. Aristotle argues the ideal form of government is a mix of the three main forms that serves the common good of all citizens, not just the interests of the ruler, wealthy, or poor. He also discusses different systems of government used in ancient city-states like Sparta, Crete, and Carthage.