No one denies that moral principles figure in legal argument and practice. However, the kind of role morality can or must play in law has been a topic of debate not only between positivists and their critics, but also within the positivist camp. The topic was brought into contemporary prominence by Ronald Dworkin, who in The Model of Rules I made the provocative observation that the legality of norms appears to depend sometimes on their substantive (moral) merits, and not just on their pedigree or social source.Ronald Dworkin, The Model of Rules I, in TAKING RIGHTS SERIOUSLY 14 (1977). The observation was intended by Dworkin as a challenge to the positivism of H.L.A. Hart.