According to a widely held view, people's commitments to laws are dependent on the existence in their community of a conventional practice of complying with certain fundamental laws. This conventionalism has significantly hampered our attempts to explain the normative practice of law. Ronald Dworkin has argued against conventionalism by bringing up the phenomenon of persistent fundamental legal controversies, but neither Dworkin nor his legal positivist respondents have correctly understood the real significance of such controversies. This article argues that such controversies (...) pose a deep challenge to any conception of our legal practice as a genuinely normative, rule-mediated, practice. The article also argues that what is needed to deflect this challenge is a new understanding – different from the widely held conventionalist understanding – of how people's commitments to laws are predicated on their fellows’ like commitments. (shrink)