  Some legal theories speak of these principles and rules as belonging to law by a kind of “conceptual” necessity. Hart (1961) can be so read. But even Hart’s account, on closer examination, identifies the relevant necessity not as conceptual or linguistic but as an instance of the rational necessity of means needed to secure purposes which are non-optional. It was for this reason that Hart spoke of them as constituting “the minimum content of natural law.” He would have expressed his own meaning more perspicuously had he spoken instead of “the minimum content of positive law, the minimum set of principles which, because rationally necessitated —given certain fundamental ‘truisms’ about human nature and the human predicament—for the securing of purposes shared by all survivable human societies, can be called natural law.” The fact is that these elements of our law are both positive (made and part of official practice) and natural (rationally required for at least minimal human flourishing).