Kelsen's "Pure Theory of Law" is widely acknowledged as his magnum opus. It aims to describe law as a hierarchy of norms which are also binding norms while at the same time refusing, itself, to evaluate those norms. That is, 'legal science' is to be separated from 'legal politics'. Central to the "Pure Theory of Law" is the notion of a 'basic norm ("Grundnorm")'a hypothetical norm, presupposed by the theory, from which in a hierarchy all 'lower' norms in a legal system, beginning with constitutional law, are understood to derive their authority or 'bindingness'. In this way, Kelsen contends, the bindingness of legal norms, their specifically 'legal' character, can be understood without tracing it ultimately to some suprahuman source such as God, personified Nature or a personified State or Nation.