CYIL vol. 8 (2017)

CYIL 8 ȍ2017Ȏ FAILURE TO REACT AS EVIDENCE OF OPINIO IURIS (practice which establishes the agreement of the parties regarding its interpretation) may amend or modify the treaty. Although this topic of the Commission falls outside the scope of the present comment, it is suggested, without going into any further detail, that some of the observations mentioned above might be relevant also in regard to the cited draft conclusion 10 [9], paragraph 2 on establishing an agreement under article 31, paragraph 3 (b) of the Vienna Convention on the Law of Treaties. The Commission itself admits, in its commentary to the draft conclusion 10 [9], para. 2, i.a. , that “the circumstances that will ‚call for some reaction‘ include the particular setting in which the States parties interact with each other in respect of the treaty”; that “[t] he significance of silence also depends on the legal situation to which the subsequent practice by the other party relates and on the claim thereby expressed”; and that “[t]he relevance of silence or inaction for the establishment of an agreement regarding interpretation depends to a large extent on the circumstances of the specific case. … decisions of international courts and tribunals demonstrate that acceptance of a practice by one or more parties by way of silence or inaction is not easily established”. 29 IX. The draft conclusions, discussed above, were adopted by the Commission only on first reading and, therefore, their final texts might be quite different. Nevertheless, it seemed useful, already at this stage, to point to the fact that, in formulating general conclusions about state practice, due attention has to be paid to the diversity and variability of such practice and its different legal significance in different contexts and circumstances and to actual motives and awareness (or lack of them) which lead states to react or fail to react to practice of other states.

The possibility of amending or modifying a treaty by subsequent practice of the parties has not been generally recognized. The present draft conclusion is without prejudice to the rules on the amendment or modification of treaties under the 1969 Vienna Convention and under customary international law.”; ILC, Report on the work of the sixty-eighth session, doc. A/71/10, p. 122, p. 121-122. In its commentary to this conclusion, the Commision, i.a. , states that “[i]n conclusion, while there exists some support in international case law that, absent indications in the treaty to the contrary, the agreed subsequent practice of the parties theoretically may lead to modifications of a treaty, the actual occurrence of that effect is not to be presumed. Instead, States and courts prefer to make every effort to conceive of an agreed subsequent practice of the parties as an effort to interpret the treaty in a particular way. …”.; ibid ., p. 180. 29 ILC, Report on the work of the sixty-eighth session, pp. 198-199.

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