a priori a 'pure part' of legal science, consisting of a framework of fundamental concepts. Then, in an empirical part of legal science, this framework would be applied to empirical (sociological, historical and so on) material so as to understand that material as 'law'. The science, in both of its parts, would also be 'pure' in a second sense, in being solely descriptive—excluding from the science any element of evaluation. The core subject matter of legal science, for Kelsen, is legal norms. He defines a 'norm' as 'the meaning of an act of will'. Thus, for Kelsen a norm does not necessarily have any element of generality—hence not all norms are rules. Indeed, as the meaning of an act of will, a norm is not intrinsically rational; departing from Kant both back toward David Hume as well as in the direction of contemporary philosophical positivism, Kelsen denies the existence of practical reason. Legal science, as Kelsen would like it to be, has to describe a legal norm without either evaluating it or adopting it as an evaluation. This can be done by distinguishing rigorously between the social statement that is the norm itself and the legal-scientific restatement of it that is, or is contained in, a description of the norm. Kelsen terms the norm itself a 'legal norm (Rechtsnorm)' and its descriptive restatement a 'legal proposition (Rechtssatz)'. Legal orders For Kelsen as for other central European contemporaries, norms occur not singly but in sets, termed 'orders'. The ordering principle of an order of moral norms—and of an order of natural law, if one could exist—would be logical, as deduction. From the general norm 'do not kill other human beings', it follows deductively that A must not kill any other human being. Kelsen calls this a 'static' order. An order of positive law, he maintains, is not, or not centrally, like that. Although it forms a hierarchy, it is 'dynamic', in that its ordering principle is authorisation. Each relatively 'higher' norm authorises someone (an individual or an organ, primarily of the state) to create further and relatively 'lower' norms. In this is found the specific characteristic of positive law, hence of all law, that it regulates its own creation. Even though positive legal norms do commonly contain elements of generality, those elements are not central to the relation between a higher and a lower norm. This is a relation of legal