   Kelsen’s problem here is not due to the fact that he was a relativist with respect to every normative system, like morality, religion etc.; it is not the scope of his relativism that is relevant to the question of reduction. The problem stems from the fact that Kelsen was quite right about the law. Legal validity is essentially relative to the social facts that constitute the content of the basic norm in each and every legal order. Notice that legal validity is always relative to a time and place. A law enacted by the California legislature only applies within the boundaries of the state of California, and it applies during a certain period of time, after its enactment and until a time when it is modified or repealed. And we can see why: because legal validity is determined by the content of the basic norm that is actually followed in a given society. The laws in UK, for example, are different from those in the US, because people (mostly judges and other officials) actually follow different rules, or basic norms, in Kelsen’s terminology, about what counts as law in their respective jurisdictions. Once Kelsen admits, as he does, that the content of a basic norm is fully determined by practice, it becomes very difficult to understand how the explication of legal validity he offers is non-reductive.