CYIL vol. 9 (2018)

CYIL 9 ȍ2018Ȏ CUSTOMARY INTERNATIONAL LAW, INTERPRETATION OF TREATIES … undertaken with a sense of legal right or obligation”. 19 Its paragraph 2 then makes a distinction of a general practice that is accepted as law by mere usage or habit. Conclusion 10 concerns the evidence from which acceptance of a given practice as law may be ascertained. It may take a wide range of forms. Paragraph 2 provides a non-exhaustive list of forms of acceptance. 20 Failure to react over time to a practice may serve as evidence of acceptance as law, provided that States were in a position to react and the circumstances called for some reaction (para. 3). Part Five deals with the significance of certain materials for the identification of customary international law (CIL). They include treaties (conclusion 11), resolutions of international organizations and intergovernmental conferences (conclusion 12), decisions of courts and tribunals (conclusion 13) and teachings (conclusion 14). Conclusion 11 reflects a classical three-fold role which treaties may play in respect of custom, i.e. codification, crystallization, or generation of a rule of customary international law. A rule set forth in a treaty may reflect a custom if it is established that the treaty rule: (a) codified a rule of CIL existing at the time when the treaty was concluded; (b) has led to the crystallization of CIL that had started to emerge prior to the conclusion of the treaty; or (c) has given rise to a general practice that is accepted as law, generating a new rule of CIL. 21 A little more complicated and controversial was the debate on the role of resolutions of international organizations and intergovernmental conferences that, according to conclusion 12, para. 1, cannot independently create a rule of CIL. However, a resolution adopted by an international organization or at an intergovernmental conference may provide evidence for determining the existence and content of a rule of CIL, or contribute to its development (para. 2). Paragraph 3 provides that a provision in a resolution adopted by an international organization or at an intergovernmental conference may reflect a rule of CIL “if it is established that the provision corresponds to a general practice that is accepted as law”. 22 Decisions of international courts and tribunals, in particular of the International Court of Justice, and teachings of the most highly qualified publicists of the various nations may serve as a subsidiary means for the determination of rules of CIL. The two last conclusions (15 and 16) seem to be the most problematic. Indeed, they gave rise to a complex debate within the ILC. The Commission finally maintained both draft conclusions from the first reading. They deal respectively with the concept of a persistent objector 23 and particular customary international law. 24 All in all, the draft conclusions on identification of CIL with commentaries are a relatively concise document, very clear and readable. On the one hand, it serves its purpose to offer practical guidance for law practitioners, including national courts. On the other hand, it may not fully satisfy some academic readers who have been waiting for a more progressive approach to customary international law, including the role of actors other than States. 19 Ibid., p. 18. 20 Ibid., p. 20: “Forms of evidence of acceptance as law ( opinio juris ) include, but are not limited to: public statements made on behalf of States; official publications; government legal opinions; diplomatic correspondence; decisions of national courts; treaty provisions; and conduct in connection with resolutions adopted by an international organization or at an intergovernmental conference.”

21 Ibid., p. 23. 22 Ibid., p. 27. 23 Ibid., p. 32. 24 Ibid., p. 34.

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