"It is clear then that... those states in which the middle element is large, and stronger if possible than the other two (wealthy and poor) together, or at any rate stronger than either of them alone, have every chance of having a well-run constitution." Thus did Aristotle summarise his analysis of the Greek city states.

The stability of what we would now call "constitutional democracy" depended on the size of its middle class. It is no accident that the United States and United Kingdom, long-stable democracies today succumbing to demagogy, are the most unequal of the Western high-income countries. Aristotle, we are learning, was right.