 One might justify the content in a variety of ways. A legal positivist might argue that the rule of recognition identifies efficiency as an appropriate ground of judge-made law. Or one might argue, as Dworkin has suggested, that efficiency provides the best interpretation of the practice governing the law of accidents. On either account, the claim that efficiency identifies the content of the law is a contingent claim. For the positivist, the content of the rule of recognition is contingent on the social practice of the relevant public officials; they may, but they need not, adopt an efficiency  criterion.[15]  Similarly, for Dworkin, the law derives from the best interpretation of the past political decisions of the community. These decisions are of course contingent; a different history of decisions might yield a different account of law. Claim (II) thus does not constitute a competing concept of law.