Reductionist views, in particular, assume that in order to shed light on the nature of law, one must explain what law is and how it works, in terms of more basic facts. As a result, first-rate legal theories succeed to the extent that they achieve this in an explicatively powerful way (Marmor 2013). The purpose of a theory of the first order is to offer, from this point of view, a metaphysical reduction of the law: that is to say, to show that the phenomenon of the law is in reality constituted by another type of phenomenon, more fundamental, and that it is completely reducible to it (in the same way that chemistry could, in principle, be reduced to particle physics). Interpreted in this way, positivism would attempt, for example, to explain the nature of the law by reducing the facts about what the law is, how it works, and what it requires to more basic social facts—for example, about people`s behavior, beliefs, and dispositions. By such a reduction, a theory such as positivism claims to illuminate the phenomenon of law itself, break it down into its components and explain how they together constitute the complex social practice of law. (On metaphysical reduction in general, see Schroeder 2007, 61-83; see also the entry on scientific reduction.) In contrast, naturalists tend not to support the informal method of testing legal theories against intuition, because their goal is to make “philosophical theorization continuous and dependent on scientific theory” (Leiter 2007, 35). Leiter argues that our intuitions about the law are too unreliable to gain much epistemic weight (as others have done with intuitions in other areas of philosophy) (Leiter 2007, 180, 184; cf. Cummins 1998). According to Leiter, philosophers should generally aim to dissect “concepts that have been confirmed by their role in the successful explanation and prediction of empirical phenomena” (Leiter 2007, 184).
Therefore, he proposes a methodology according to which “the . Social science literature on law. to see which legal concept plays a role in the most powerful explanatory and predictive models of legal phenomena such as judicial behaviour” (Leiter 2007, 184). However, this methodological view raises the question of why the philosopher of law should only examine legal behavior and not anything else. In general, the naturalist owes a report on which features of the law require the most explanation and why. However, the most interesting and, from a positivist point of view, the most problematic aspect of legal principles is their moral dimension. According to Dworkin`s theory, principles, unlike legal rules, which may or may not have something to do with morality, are essentially moral in their content. In fact, it is partly a moral consideration that determines whether a legal principle exists or not. What for? According to Dworkin, there is a principle of law if that principle results from the best moral and political interpretation of past judicial and legislative decisions in the area concerned. In other words, legal principles occupy an intermediate space between legal norms and moral principles. Legal regulations are drawn up by recognized institutions and their validity results from their source.
Moral principles are what they are by virtue of their content, and their validity depends purely on the content. Legal principles, on the other hand, derive their validity from a combination of source and substantive considerations. As Dworkin put it in the most general terms, “According to the law as integrity, legal propositions are true if they are contained in or flow from the principles of justice, fairness and due process that offer or derive from the best constructive interpretation of the legal practice of the community” (Dworkin 1986, 225). The validity of a legal principle then derives from a combination of facts and moral considerations. The facts concern past legal decisions that have taken place in the area in question, and moral and political considerations concern how these past decisions can best be explained by good moral principles. The extent to which law can actually guide behavior by providing its subjects with reasons to act was questioned by a highly influential group of jurists in the first half of the 20th century, the so-called school of legal realism. American legal realists have argued that our ability to predict the outcome of legal cases based on legal norms is rather limited. In the most difficult cases, which are usually decided by the courts of appeal, the legislation itself is radically uncertain as to the outcome of the cases.