  To understand Habermas's mature positions, we must start with his Theory of Communicative Action (TCA), a two-volume critical study of the theories of rationality that informed the classical sociologies of Weber, Durkheim, Parsons, and neo-Marxist critical theory (esp. Lukács, Horkheimer, Adorno). In TCA we find Habermas's conception of the task of philosophy and its relation to the social sciences—a conception that still guides much of his work. While TCA defends the emphasis on normativity and the universalist ambitions found in the philosophical tradition, it does so within a framework that includes particular sorts of empirical social research, with which philosophy must interact. Philosophers, that is, must cooperate with social scientists if they are to understand normative claims within the current historical context, the context of a complex, modern society that is characterized by social and systemic modes of integration. By recognizing both modes of integration, one avoids the pessimism associated with theories of modernity whose one-sided, primarily instrumental conception of rationality misses the cultural dimension of modernization.