This dissertation turns to the reception of Kant’s ideas among a legacy of thinkers in the tradition of radical social thought in modern Germany to ask how we should understand the role of substantive, philosophical accounts of emancipation in a modern, democratic politics. It turns to this legacy to provide a fuller picture of their conceptions of social transformation and Kant’s unique place within them. Kant and his followers were distinct in advocating that we formulate emancipation as a contingent ideal, rather than the result of a larger historical process. The dissertation analyzes debates that unfolded between a range of intellectual schools in the tradition of radical social theory in Germany during moments of radical political upheaval and change: from the French Revolution to 1848 to World War I and Weimar. Returning to this history, I recuperate a tradition of political thinking that defended the necessity of ideals to popular movements for emancipation. Although many twentieth century theorists understand Kant to represent a discredited mode of political theorizing that seeks to subordinate politics to morality or relies on a grand narrative of history, this dissertation shows how theorists in the nineteenth and early twentieth century repeatedly turned to Kant to critique these impulses in the burgeoning utopian and Marxist social movements of their day. At various periods of social crisis in Germany, a range of political thinkers turned to Kant’s Critical philosophy to argue that emancipation was not the inevitable outcome of reason or history, but a contingent end that must be pursued through collective democratic efforts. Turning to thinkers from Kant to Heinrich Heine and Eduard Bernstein to Carl Schmitt, this dissertation recovers a legacy of political theorizing that sought to understand the limits and possibilities of popular agency in moments of social crisis in modern Germany. In returning to this archive, I argue for the importance of an account of political ideals that sees them as dependent on the kinds of collective action available to agents embedded in contexts of plurality and contingency.