He can illustrate the philosophical challenges of legal positivism by comparing it to a number of other theses with which it is sometimes misidentified, and not only by its opponents (see also Hart 1958, Füßer 1996 and Schauer 1996). These three theses establish links between law and morality that are both necessary and of great importance. Each of them is consistent with the positivist thesis that the existence and content of the law depend on social facts, not on the merits of the law. Each of them contributes to the understanding of the essence of the law. The once popular idea that legal positivism insists on the separability of law and morality is therefore a significant mistake. Ronald Dworkin rejects the social facts thesis of positivism on the grounds that there are certain legal norms whose authority cannot be explained by social facts. When ruling on difficult cases, for example, judges often invoke moral principles which, according to Dworkin, do not derive their legal authority from the social criteria of legality contained in a rule of recognition (Dworkin 1977, p. 40). However, since judges are required to take these principles into account where appropriate, they must be characterized as law. Thus, Dworkin concludes: «If we treat principles as a law, we must reject the first principle of positivists that the law of a community differs from other social norms by a test in the form of a master rule» (Dworkin 1977, p.
44). Dworkin argues that when deciding difficult cases, judges often rely on principles of law that do not derive their authority from an official enactment (Dworkin 1977, p. 40). According to Dworkin, these principles must be qualified as law because judges are required to take them into account when they are relevant. But if the proclaimed legal principles do not represent the law, then it is false, contrary to the pedigree thesis, that a legal declaration is valid only because it has been officially promulgated. According to the thesis of conventionality, it is a conceptual truth about the law that legal validity can ultimately be explained in the form of criteria that are decisive on the basis of a kind of social convention. For example, H.L.A. Hart (1996) argues that the criteria for legal validity are contained in a recognition rule that establishes rules for the creation, amendment and decision of the law.
In Hart`s view, the rule of recognition under a convention among public servants is authoritative for considering their criteria as standards governing their conduct as public servants. Although Joseph Raz does not seem to support Hart`s view of a master`s recognition rule that includes the criteria of validity, he also believes that the criteria of validity are authoritative only on the basis of an agreement between officials. More importantly, Hart argues that Austin neglects the existence of secondary meta-rules that deal with the primary rules themselves, distinguishing full-fledged legal systems from primitive legal systems: the ClS (Critical Legal Studies) movement seeks to extend the radical aspects of legal realism into a Marxist critique of mainstream liberal jurisprudence. CLS theorists believe that realists underestimate the extent of indeterminacy; While realists believe that indeterminacy is local in the sense that it is limited to a particular class of cases, CLS theorists argue that law is radically (or globally) indefinite in the sense that the class of available legal documents rarely, if ever, logically/causally produces a single result. As mentioned above, Dworkin`s arguments against positivism depend on assertions about the phenomenology of jurisprudence and the limits imposed on jurisprudence by legal disagreements. Mark Greenberg`s recent work is based on many of Dworkin`s claims, but his conclusions are more radical in several ways (see Greenberg 2004 and 2014). Greenberg`s central argument against positivism is methodical: no one, he argues, would deny that the content of the law depends, at least in part, on social facts. The question of which facts – for example, the semantic content or the intended effect of legislation – are not determined by reference to other facts: «Legal practices. cannot determine their own relevance» (2004:185).
It is therefore necessary to appeal to other types of considerations – for Greenberg, to reflections on the moral significance of our social practices. It is the fault of positivism to claim that the law could be oriented towards practice to the end. However, the fact that the content of the law depends on social sources is a truth that is usually confirmed by the law, as opposed to the fact that it is established in local legal practice. There is a categorical difference between the validity of the source thesis – a truth about the law as a kind of social practice – and the claim that in the UK, for example, it is legally illegal to drive more than 70 miles per hour on the motorway. In this way, the first explains the second without circularity and without the need to appeal to morality. The law on an issue is established when legally binding sources provide its solution. In such cases, judges are generally said to apply the law, and since it is source-based, its application involves technical and legal skills to argue from these sources and does not require moral insight. If a legal question is not answered by norms from legal sources, then a legal answer is missing – the law on these issues is unclear.
When ruling on such cases, courts inevitably take new (legal) paths and their decision develops the law. Of course, their decisions in such cases are based, at least in part, on moral and other extrajudicial considerations (Raz 1979, pp. 49-50). The second thesis, which encompasses the basis of legal positivism, is the separability thesis. In its most general form, the separability thesis asserts that law and morality are conceptually separated from each other. This abstract formulation can be interpreted in several ways. For example, Klaus Faber (1996) interprets it as a meta-level assertion that the definition of law must be completely free of moral notions. This interpretation implies that any reference to moral considerations in the definition of related terms of law, validity and the legal system is incompatible with the divisibility thesis.