  Thus, elucidating the conditions of legal validity and explaining the normativity of law form the two main subjects of any general theory about the nature of law. In section 1, we will explain some of the main debates about these two issues. In section 2, we will discuss some of the methodological debates about the nature of general jurisprudence. In the course of the last few centuries, two main rival philosophical traditions have emerged about the nature of legality. The older one, dating back to late mediaeval Christian scholarship, is called the  natural law tradition. Since the early 19th century, natural law theories have been fiercely challenged by the  legal positivism tradition promulgated by such scholars as  Jeremy Bentham and  John Austin. The philosophical origins of legal positivism are much earlier, though, probably in the  political philosophy of Thomas Hobbes. The main controversy between these two traditions concerns the conditions of legal validity.  Basically, legal positivism asserts, and natural law denies, that the conditions of legal validity are purely a matter of social facts. In contrast to positivism, natural law claims that the conditions of legal validity are not exhausted by social facts; the moral content of the putative norms also bears on their legal validity. As the famous dictum, commonly attributed to Saint Augustine, has it: lex iniusta non est lex (unjust law is not law). (Augustine, De Libero Arbitrio, I, 5; see also Aquinas, Summa Theologica, I-II, Q. 96, Art. 4.) 