 Kelsen’s most important contribution lies in his attack on reductivism and his doctrine of the “basic norm”. He maintains that law is a normative domain and must understood as such. Might does not make right—not even legal right—so the philosophy of law must explain the fact that law imposes obligations on its subjects. Moreover, law is a normative system: “Law is not, as it is sometimes said, a rule. It is a set of rules having the kind of unity we understand by a system” (1945 [1961: 3]). For the imperativalists, the unity of a legal system consists in the fact that all its laws are commanded by one sovereign. For Kelsen, it consists in the fact that they are all links in one chain of authority. For example, a by-law is legally valid because it is created by a corporation lawfully exercising the powers conferred on it by the legislature, which confers those powers in a manner provided by the constitution, which was itself created in a way provided by an earlier constitution. But what about the very first constitution, historically speaking? Its authority, says Kelsen, is “presupposed”. The condition for interpreting any legal norm as binding is that the first constitution is validated by the following “basic norm:” “the original constitution is to be obeyed”. Now, the basic norm cannot be a legal norm—we cannot explain the bindingness of law by reference to more law without an infinite regress. Nor can it be a social fact, for Kelsen maintains that the reason for the validity of a norm must always be another norm—no ought from is. It follows, then, that a legal system must consist of norms all the way down. It bottoms in a hypothetical, transcendental norm that is the condition of the intelligibility of any (and all) other norms as binding. To “presuppose” this basic norm is not to endorse it as good or just—presupposition is a cognitive stance only—but it is, Kelsen thinks, the necessary precondition for a non-reductivist account of law as a normative system.