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Customary international law is one of the two main sources of international law. Yet there remains considerable uncertainty about the process through which rules of custom emerge or subsist – the ‘meta-law of custom’, which is now under consideration within the un International Law Commission (ilc). This article does not rehearse arguments about these uncertainties nor indeed engage with the current work of the ilc. Instead, it focuses on areas of certainty, viz. aspects of the law of meta-custom that are generally agreed and on which the ilc can draw. It argues that this certainty is the product of decades of jurisprudence, first of the Permanent Court and then of the International Court of Justice. In highlighting four crucial contributions and situating them in the debate about judicial law-making, this article seeks to raise awareness for the World Court’s (often unacknowledged) role in shaping the meta-law of custom.

Meta-Custom and the Court: A Study in Judicial Law-Making

in The Law & Practice of International Courts and Tribunals



  • 2

    Martti Koskenniemi“Introduction” in Id. (ed.) Sources of International Law (2000) xxi.

  • 10

    In 2011the International Law Commission decided to include the topic in its long-term programme of work: see its 2011 Report un Doc. A/66/10 paras. 365–367. The General Assembly took note of this decision in ga Res. 66/98.

  • 23

    Pelletsupra note 7 mn 211.

  • 24

    Wood First Reportsupra note 13 para. 54.

  • 28

    Wood “Second Report”supra note 13 para. 21.

  • 29

    Wood “Second Report”supra note 13 para. 3(a).

  • 33

    See Pelletsupra note 7 his fn. 570: “The Committee did not pay much attention to the question of customary law and only very little can be deduced from the Procès-verbaux on this point.” Manley O. Hudson remarked that the drafters of the Statute “had no very clear idea as to what constituted international custom”: ilc Yearbook (Vol. i 1950) 6 para. 45.

  • 35

    Baron Descamps Procès-Verbauxsupra note 34 322.

  • 36

    Haggenmachersupra note 31 31.

  • 39

    See Haggenmachersupra note 31 70 and Crawford supra note 30 54–55. Both refer to Dionisio Anzilotti Cours de droit international public (1929) 73: “Lorsque cette volonté se manifeste par la constante répétition d’une manière donnée d’agir dans des circonstances données on parle plus proprement de coutume (tacitum pactum): règle observée en fait avec la conviction d’observer une norme juridique” (emphasis added).

  • 47

    Pelletsupra note 7 mn 214.

  • 49

    Paul Guggenheim“Les deux éléments de la coutume internationale” in La technique et les principes du droit public: Etudes en l’honneur de Georges Scelle (Vol. 1 1950) 275.

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  • 53

    Pelletsupra note 7 mn 211.

  • 69

    Pelletsupra note 7 mn 212.

  • 70

    Wood “Second Report”supra note 13 para. 51 (draft conclusion 8). According to the Chairman of the ilc’s Drafting Committee (supra note 13) “[t]he term ‘general’ . . . is the fundamental adjective qualifying practice in the context of the determination of the existence and content of a rule of customary international law. This adjective means that a practice needs not to be universally followed for a customary international rule to emerge but that it needs to be extensive or ‘sufficiently widespread and representative’ ”.

  • 72

    Chengsupra note 48 at 23. See the useful discussion in Niels Petersen “Customary Law without Custom” 23 American University International Law Review (2008) 275 280–283.

  • 73

    Wood “Second Report”supra note 13 para. 58.

  • 75

    Dillardsupra note 60.

  • 76

    Crawfordsupra note 30 49. For similar observations see Petersen supra note 72 277 (“it seems practically impossible to ascertain the practices of the nearly 200 states in the international community”).

  • 77

    Cf. Crawfordsupra note 30 49.

  • 79

    See e.g. Thirlway“Codification”supra note 7 at 58: “State practice as the material element in the formation of custom is it is worth emphasizing material: it is composed of acts by States with regard to a particular person ship defined area of territory each of which amounts to the assertion or repudiation of a claim relating to a particular apple of discord”.

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  • 95

    Koskenniemisupra note 93.

  • 125

    Tomkasupra note 40.

  • 128

    Cf. Crawfordsupra note 30 49.

  • 129

    Worstersupra note 25; Roberts supra note 25.

  • 130

    Talmonsupra note 25 21.

  • 132

    Parlettsupra note 16 104–106.

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