The debate about positivism in general legal theory or in the international legal scholarship manifests so many different, if not conflicting, meanings of positivism—even among legal positivists themselves—that the debate about legal positivism has proved almost unfathomable and unintelligible.

No other approach to theorizing international law is more closely associated with and dependent upon the development of an account of its sources than is positivism. The explanation for this is a simple and familiar one: if there is any thesis regarding (p. 324) law that we can uncontroversially associate with the label ‘legal positivism’, it is the view that a norm’s status as law, its membership in a legal order or system, is solely a matter of its social source without regard for its merit. Whatever their differences (and as the above epigraph attests, they are many), all legal positivists maintain that law is necessarily posited, made, or created, not discerned in the natural order of things or deduced from principles knowable a priori. What counts as a law-creating act in any given legal system depends on the practice of its legal officials; the sources of law are, in this sense, a contingent or arbitrary matter.

Commitment to even this relatively modest claim brings with it substantial argumentative burdens. Specifically, it requires international legal positivists to offer the following: (a) a defence of the claim that law must have a social source; (b) an argument outlining the possible sources of law—that is, those act-types that can count as positing or creating law; and (c) an argument defending or rejecting the existence of specific sources of law in a specific legal system; e.g. an assessment of the claim that general principles of law serve as a source of international law. Clearly a comprehensive treatment of these issues requires more than a single book chapter, or for that matter a single book. Instead, the present work offers partial treatments of the first two of the argumentative tasks mentioned as incumbent upon international legal positivists.

I begin by considering the case for legal positivism; again, understood as the relatively modest thesis that the existence of law is a matter of its social source, regardless of its merits. Arguments for this thesis are of three types: descriptive (or social scientific), normative (or ethical), and conceptual (or metaphysical). I aim not to adjudicate between these arguments but to demonstrate that what follows for the sources of international law from the commitment to positivism depends to a considerable extent on the specific defence offered for accepting it as an account of the nature of law, including international law. In section III: Customary International Law Creation: Orthodox and Informal Legislation Accounts, I focus specifically on the possibility of customary international law. Though few dispute that custom can, and does serve as a source of international law, there is widespread disagreement regarding the precise mechanism whereby customary legal norms come to exist. If they are to defend custom as a source of international law, positivists owe us a plausible account of how customary rules are made; i.e. what acts count as the positing or making of customary norms, and how they do so. I argue that neither the orthodox account of customary law formation nor those accounts in which judges make law based on a belief in a broad consensus regarding the desirability of there being such a law do so. The former fails to identify an act of positing or creation at all, while the latter is better characterized as informal legislation than as custom formation. I then (p. 325) sketch a third approach that characterizes customary norms as elements of a community’s normative practice, and custom-formation as normative interpretations of patterns of behaviour that are successfully integrated into that normative practice. This account avoids the chronological paradox in custom formation and accounts for various features commonly associated with custom, such as its binding agents even in the absence of consent. But is it compatible with legal positivism? I offer a preliminary argument for an affirmative answer, focusing particularly on its compatibility with the rationales Hans Kelsen and Joseph Raz offer for legal positivism.

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© 2017, Oxford University Press. This material has been published in Oxford Handbook on the Sources of International Law, eds. Samantha Besson and Jean D’Aspremont. (Oxford: Oxford University Press, 2017): 323-41. Not for re-distribution or re-use.

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Lefkowitz, David. “Sources in Legal Positivist Theories,” in Oxford Handbook on the Sources of International Law, eds. Samantha Besson and Jean D’Aspremont. (Oxford: Oxford University Press, 2017): 323-41. DOI: 10.1093/law/9780198745365.003.0016

The definitive version is available at: Oxford University Press