This chapter discusses secularization as secularism, that is, as an invidious and differential naming that places societies in a temporal sequence of more or less rationalization and modernization. Here Jürgen Habermas aims to show why secularization theory has been mistaken on several accounts and why we must attenuate and revise some of its major claims. In short, how secularization is conceived in relation to the social order, the sources of normative concepts and the very foundations and limits of political power, discloses strikingly and pointedly how social evolution is conceptualized. Alternatively, secularization theory becomes a seismograph that registers the links between rationalization and the evolution of society, and with them, personality structures and ever more transparent social institutions of political self-legislation. The chapter concludes with an analysis of Habermas's development of what he calls a "postsecular" self-understanding of modern societies, which is tied to a rethinking of the traditional tethering of rationalization to modernization, and these in turn to secularization.