Politics

Where Plato imagined the ideal state, Aristotle counted the real ones. He gathered the constitutions of the Greek world and asked what actually held a government together and what pulled it apart. The result is the first comparative politics, empirical and patient. His definition of the citizen, one who rules and is ruled in turn, is still the cleanest statement of what a republic asks: not just to be governed, but to take a turn at governing.

Plato's student, and his opposite in method. Where Plato reasoned toward the ideal, Aristotle collected. He and his school gathered the constitutions of more than a hundred and fifty Greek states and asked what actually held them together and what tore them apart. The result is the first comparative political science. His definition of the citizen, one who rules and is ruled in turn, is still the cleanest sentence anyone has written about what membership in a republic asks of a person.