Induction, Assertion and the Limits of the Existing Methodologies to Identify Customary International Law

Professor Talmon’s article on the methodologies employed by the International Court of Justice to ascertain custom is as important as it is timely now that the International Law Commission is advancing with its study on the identification of customary international law. To contribute to the debate, I propose to elaborate on a crucial question that the piece raises. Why is it that the Court so often resorts to ‘asserting’ customary international law instead of providing more robust reasoning to back up the rules that it identifies? Though the precise reasons why the Court takes the approach it does are a matter for speculation, I suspect that this has to do with limitations that are inherent to the standard methodology to establish custom (the ‘inductive method’, to use Professor Talmon’s terminology), in the shaping of which the Court itself has played a large part.

As Professor Talmon suggests, systemic reasoning – argument by principle and argument by analogy – has been a major catalyst for development in international law, filling gaps that would be left behind if the inductive method were applied. Yet, the inductive method is the best accepted methodology to identify custom insofar as it encapsulates the prevailing view as to what is required by the ‘rule of recognition’ of international law.

The problem with that ‘rule of recognition’ is that it does not allow us to reach any firm conclusions as to the existence of particular rules of custom. That becomes clear when one dissects the inductive method as defined and applied by the International Court. In North Sea Continental Shelf and Military and Paramilitary Activities in and against Nicaragua we were told that State practice must be ‘extensive’ and ‘virtually uniform’ or, at best, ‘general’ albeit not perfect. Opinio juris has to be proven independently, and the Court is not keen to infer it from mere adherence by States to the practice. In a world of over 190 States, what does it take for one to conclude persuasively that general practice has emerged accompanied by the required sense of obligation? Can any rule – even those long viewed as established – survive the brutal scrutiny of the magnifying glass? Whenever one looks at practice and opinio juris too closely, putative rules are more likely to dissolve than to coalesce. This is a serious deficiency of a decentralised legal system whose membership has been steadily expanding.

When one reflects about the shortcomings of the prime method to identify rules of international law, it becomes easier to contextualise what the International Court has been doing. Unsurprisingly, with the notable exception of Nicaragua and cases involving special custom such as Right of Passage and San Juan River, the Court tends to apply the inductive method in order to reject claims of customary international law. If the Court were to apply the inductive method more liberally to affirm new rules of custom, its reasoning would be more exposed to criticism. Has it cited enough instances of practice? Where has it found the opinio juris? As obscurantist a form of reasoning though it may be, assertion capitalises on the position of authority in which the Court finds itself as the principal judicial organ of the United Nations and the only international tribunal with general jurisdiction. It allows the Court to clarify the law incrementally while keeping the level of institutional criticism at a chronic (but arguably manageable) level. At best, the judgment sends the message that the Court has heard the parties, pondered the issues and come to a sensible conclusion. If a similar dispute arises in the future, the position to which the Court arrived will be regarded as authoritative and unlikely to attract much controversy.

But is that good enough? The question that arises for the profession is what we would prefer the Court to be doing when it comes to establishing rules of international law (and where, one might add, systemic reasoning cannot offer a persuasive solution). One alternative is to insist that the Court apply the inductive method as developed in its case law, but that comes with the risk that fewer and fewer rules of international law will be identified by the Court. Another would be for the Court to step up and revisit the inductive method with a view to making it more practical and faithful to what has been (presumably) done behind the scenes. That could be done along the lines of Judge Lachs’ dissent in North Sea (representative practice by a sizable number of States suffices) or of Hersch Lauterpacht’s notion of ‘progressive interpretation’ of State practice. The problem here is the risk of backlash on the part of States given that a high threshold for establishing custom safeguards sovereign equality. Might States start objecting if the Court were to endorse a more relaxed test? At the present stage of the development of international law, the Court’s use of assertion may well serve a useful purpose towards the fulfilment of the ideal of an ‘international rule of law’, even if every instance of its application will inevitably raise rule of law concerns.

Given the hurdles that any attempt at reform is bound to face, one might ask how far can any doctrinal inquiry into the methodologies applied by the International Court get us (or, for that matter, the ILC). Can we get past the walls or are we doomed to keep hitting them? Professor Talmon’s article serves as a reminder that it is important that we continue watching the International Court closely, finding new ways to reflect on what the Court does and how it does it. His typology of methodologies and analysis of the interplay between methods carry the debate further and provide a source of inspiration and a helpful starting point for future reflection.