The Debate in the Sixth Committee on the Formation and Evidence of Customary international Law


On 6 November 2012, during the debate in the Sixth Committee of the UN General Assembly on the Report of the International Law Commission, the Legal Adviser to the Permanent Mission of Italy, Mr Salvatore Zappalà, submitted the comments of his delegation on the work conducted by the ILC on the “Formation and Evidence of Customary International Law”. He affirmed he was confident that the Special Rapporteur would be able to provide ample information on the topic, and he said:

It is hard to deny that it is an issue that is both important and appealing; however, in light of its complexity caution should be exercized in formulating any reasoning that may restrict the action of judges at the international and domestic level, as well as other interpreters. One of the distinctive traits of customary law is that it emerges in a nearly spontaneous manner, through the ‘interaction’ of a variety of actors and taking into account a variety of factors. The temptation to build predetermined drawers or procedures may result too artificial to be useful. The very nature of international law requires the possibility to identify the rule in every relevant legal act or fact.

The idea to make a study in this area can still be useful to analyze a list of elements that concur to the formation and evidence of international customary law, but we hardly see this as an exhaustive process.

While it may be both feasible and useful to develop a compilation of practice in a determined field of international law, with the purpose of codifying customary law, such as e.g. the monumental work of the ICRC on International Customary Law in the area of IHL; the attempt to develop a sort of meta-language on the formation and evidence of international customary law in general may be too broad and may turn out to be unduly constraining. It would run contrary to the essence of general international law as spontaneous law (which is the necessary toile de fond of international relations and cannot be circumscribed by a codification exercise); in particular such strict determination with regard to rules of customary law in statu nascendi may run contrary to necessary developments of international law.

Even though developing principles on how to gather evidence on customary international rules might be less controversial, it should be kept in mind that a great degree of flexibility should be left to the interpreter in this area. It is the reasoning and the materials identified that attest to the credibility of the statement and not any procedural device that may end up obfuscating the strength of realities.

The problem is not so much to determine that there is a set of sources or predetermined elements that assist in identifying the formation or evidence of customary law but it is more whether doing so implies that other elements can be excluded. Some of these elements or their balance may change over time, and may depend on the advances in technologies and on the context in which principles and rules emerge, or the values embodied in certain rules, or the frequency of certain events. In some areas opinio iuris may be stronger (and more relevant) than actual practice, in other cases there may be practice which lacks clear expressions of opinio. A thorough mapping exercise is not easy, and the results may be less satisfactory than expected. Nonetheless, we stand ready to contribute to the efforts of the Special Rapporteur in this area and will make available our reflections to this end.

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