The author revisits H. L. A. Hart's theory of positive law and argues for a major qualification to the thesis of the separation of law and morality based on a concept of systemic legitimacy derived from the social theory of Jurgen Habermas. He argues that standards for assessing the degree of systemic legitimacy in modern legal systems can develop through reflective exercise of “critical legality,” a concept coined to parallel Hart's “critical morality,” and an expanded understanding of the “external” and (...) “internal” perspectives on legal systems. Following Habermas, he argues that modern positive law must retain systemic legitimacy. After suggesting criteria for measuring systemic legitimacy, the author concludes that the concept provides a useful approach to contemporary problems of “lawless” regimes and “law's imperialism.”. (shrink)