Equality has always been the most powerful political idea in America, and it is becoming the most powerful idea in the world. Observers from Alexis de Tocqueville to the most recent social critics have commented upon the idea's great force. Yet, for all its influence upon popular ideology, the idea of equality becomes a bundle of contradictory impulses once it is applied to public policy and social institutions. As the title of this lively book suggests, equality becomes equalities.

Once inequality is established, there is a deep difference between equal policies and policies that...