Aristotle, in his seminal work 'Politics,' extensively analyzed the causes of political instability and revolution (stasis). He indeed identified inequality as a primary and pervasive cause of revolutions, a keen observation that remains relevant across millennia. For Aristotle, revolutions arise from a sense of injustice, particularly when there is a perceived imbalance in the distribution of honor, wealth, or power among citizens.

He distinguished between two main forms of inequality that fuel discontent: numerical inequality and proportional inequality. Numerical inequality refers to the sheer disparity in numbers between the rich and the poor, where a large, impoverished majority feels exploited by a small, wealthy elite. Proportional inequality, on the other hand, relates to the perception that individuals or groups are not receiving their due share of political power or resources relative to their merit or contribution to the state. For instance, the wealthy might feel entitled to more power due to their property, while the poor might demand equality based on their status as free citizens.

Aristotle argued that both the desire for absolute equality (among the poor) and the desire for superiority (among the rich) can lead to revolutionary fervor. When either group feels unjustly treated or deprived of what they believe is their rightful share, they become ripe for rebellion. He noted that democracies are prone to revolutions when the poor rise against the rich, and oligarchies when the rich oppress the poor. Thus, for Aristotle, maintaining a stable polity required a careful balancing of these competing claims and a degree of proportional equality, often best achieved through a mixed constitution or a strong middle class, to mitigate the destabilizing effects of extreme inequality.