Revolutionaries, counter-revolutionaries, and reformers the world over appeal to democracy to justify their actions. But when political factions compete over the right to act in "the people's" name, who is to decide? Although the problem is as old as the great revolutions of the seventeenth and eighteenth centuries, events from the Arab Spring to secession referendums suggest that today it is hardly any closer to being solved. This book defends a new theory of democratic legitimacy and change that provides an answer. Christopher Meckstroth shows why familiar views that identify democracy with timeless principles or institutions fall into paradox when asked to make sense of democratic founding and change. Solving the problem, he argues, requires shifting focus to the historical conditions under which citizens work out what it will mean to govern themselves in a democratic way. The only way of sorting out disputes without faith in progress is to show, in Socratic fashion, that some parties' claims to speak for "the people" cannot hold up even on their own terms. Meckstroth builds his argument on provocative and closely-argued interpretations of Plato, Kant, and Hegel, suggesting that familiar views of them as foundationalist metaphysicians misunderstand their debt to a method of radical doubt pioneered by Socrates. Recovering this tradition of antifoundational argument requires rethinking the place of German idealism in the history of political thought and opens new directions for contemporary democratic theory. The historical and Socratic theory of democracy the book defends makes possible an entirely new way of approaching struggles over contested notions of progress, popular sovereignty, political judgment and democratic change.