These 11 essays by noted philosophers and social theorists take up the philosophical aspects of Jürgen Habermas's unfinished project of reconstructing enlightenment rationality. They range in subject matter from classical problems to contemporary debates, covering historical perspectives, theoretical issues, and post-enlightenment challenges. A companion volume of essays will take up the cultural and political aspects of the work. Together, the two volumes underscore the richness and variety of Habermas's project. ContributorsKarl-Otto Apel, Richard J. Bernstein, Peter Bürger, Martin Jay, Thomas McCarthy, Herbert Schnädelbach, Charles Taylor, Michael Theunissen, Ernst Tugendhat, Albrecht Wellmer