The chapter provides a detailed description and critical discussion of Habermas' attempts to make the theory of communicative action and discourse ethics fruitful beyond the narrower moral and ethical realm and, conversely, to find confirmation for it in empirical theories. Habermas refers to the research areas of psychology and social evolution and to political and sociological issues around which the “Critical Theory of Society” is to take concrete form. Concerning psychology, he develops or adopts theories of ego-development, moral development and “communication pathologies”. As it concerns social evolution he proposes theories of hominisation and socio-cultural evolution. In dealing with the political and sociological issues he is most productive, offering a theory of social order, his famous colonialisation thesis, his discourse theory of law and the constitutional state, and his theory of modernity.