Habermas contrasts his view with that of Weber, who concludes that modern law is separated from morality. This article first discusses the relationship between morality and law as conceived by Habermas. The problem is how legality can claim legitimacy, a questions that Weber tried to solve with his theory of the formal rationality of modern law. Habermas's solution is the concept of a procedural rationality. The critique then examines Habermas's conception of the relationship between law and society within a normative view of modern law. The relationship between system and lifeworld -- this central Habermasian distinction -- is approached from the perspective of a law claiming procedural rationality. Habermas's theory that the role of law is to interface between system and lifeworld is then discussed along with some aspects of his view of a 'Rechtsstaat' suited for complex societies. The author then offers some sociological criticisms against a too normativistic view of procedural legitimacy and shows that the current discussion on modern law is itself part of the development of modern law. The author's assumption is that theoretical conceptualizations of modern law offer a new legitimating base of law. For a comment on this critique, see NCJ-118721. 29 references.