There is hardly any other discipline where the central concept is as controversial as that of law. The broad variety of definitions is just an illustration, as is the fact that many authors have resisted presenting a strict definition and prefer a more general approach of conceptual analysis. Some authors have described law as a practice or an activity: ‘the enterprise of subjecting human conduct to the governance of rules’ (Fuller); an argumentative practice and an interpretive enterprise (Dworkin); a practice oriented towards the ideal of legality (Selznick).1 Others have described it as a hierarchical or institutionalized system of norms (Kelsen and Raz), or as the union of primary and secondary rules (Hart).2 And it is not only legal theorists that have trouble defining the law. If we ask ordinary citizens, some refer to the collection of rules found in statutes, others to law-enforcement institutions like courts and the police. Some may also make reference to ideals of justice.