Book 4 — The Varieties and the Best Practicable

Book 4 opens with a methodological point. The political scientist, like the doctor or the trainer, must know not only what is absolutely best but what is best under given conditions — what constitution is best for this city, with these people, at this moment. The inquiry therefore has three levels: the absolutely best, the best under actual conditions, and the best achievable by any city with any starting point. Books I–III addressed the first; Books IV–VI address the second and third.

Most of Book 4 works through the varieties of democracy and oligarchy. Aristotle identifies four types of democracy, ranging from the best (agricultural democracy, where the poor are too busy farming to attend the assembly and so leave effective power to the notable) to the worst (extreme democracy, where pay for assembly attendance floods governance with the idle urban poor). He identifies four types of oligarchy, ranging from moderate property qualifications to hereditary oligarchy to dynastic rule. In both cases, the varieties arise from the composition of the citizen body: different combinations of the poor, the middling, the rich, artisans, farmers, and merchants produce different constitutional mixtures.

The book's most important argument comes in the chapters on polity and the middle class. Polity — the mixed constitution that borrows elements from both oligarchy and democracy — is the most stable form for most cities because it is the constitution in which the middle class is strongest. The very rich and the very poor are both temperamentally unfit to govern well: the rich command despotically, the poor submit slavishly. The middle citizen, with moderate property and experience of both ruling and being ruled, governs in the interest of the whole. Cities in which the middle is small inevitably polarize between oligarchy and democracy and fall to tyranny. Cities in which it is large resist revolution because those who hold power have too much to lose and not enough to envy.