The International Court of Justice and the International Customary Law Game of Cards

Theorizing customary international law as a formal source of law makes it possible to think of it as an integrating, anti-particularistic element of the international legal order: a potential antidote to fragmentation. On the other hand, enrolling customary law in the fight against fragmentation entails the need to define as neatly as possible the contours of an orthodox conception of custom as a source of law in a formal sense, and to close ranks around it. The recent International Law Commission’s bid to establish signposts for custom formation and identifi- cation suggests that such an entrenchment has reached an advanced stage of institutionalization. What role is International Court of Justice (ICJ) playing in this respect? The ICJ may wish to make the rest of the international legal milieu believe that there is only one method for finding out custom – its own method – and that may well be its strategy. Be that as it may, one thing is clear: if the ICJ aspires, as it were, to the role of a methodological lighthouse, it must have a recognizable method, one that is intelligible enough to be replicated by other law-applying agencies. The ICJ’s judicial output may lead to higher degrees of overall systemic coherence by stimulating uniform application of customary international law in two hypothetical ‘modes-of-play’.The first one,which may be called ‘structural’, would consist in working out a method for the identification of customary rules that is detailed and unambiguous enough as to reduce the risks of divergent rulings by other courts and tribunals to a minimum. On this score one is always tempted to argue that the intrinsic indeterminacy of the customary process places limits on attempts at defining bright-line criteria. This paper tries to dispel this ordinary misconception. The second mode-of-play, which may be described as ‘incremental’, would not commit the ICJ to go beyond a broad-brush characterization of the customary process like the one that made its judgment in the 'North Sea Continental Shelf' cases so prominent. The Court’s opinions about the content of customary law would be widely accepted not on account of the method underpinning them – which may well remain a mystery, or be just a bluff – but as a consequence of the Court’s authoritativeness. In this paper, I contend that the ICJ has acted with extreme caution on both fronts, thus failing to strengthen or stabilize international law’s putative ‘centre’. In the tense atmosphere so typical of the international customary law poker game, the Court has been playing its cards close to its chest. And the attitude of its fellow players – the International Law Commission (ILC), doctrine, and States – is not fundamentally different. Not blessed with a good hand, the ILC and doctrine sit nervously at the table and keep a watchful eye on States and the Court, both of which wear a poker face. Here I say something about the vain search for a ‘framework custom’, understood as the product of a uniform practice of States concerning the identification of customary rules, taking into account, inter alia, the first reactions of States to the inquisitive attitude lately taken by the ILC in its work on the topic. Afterwards, I try to expose the predicament of international legal doctrine, suspended as it is between a scientific outlook on the game and an emotional approach to the authority of the ICJ, before concluding by imagining what a showdown would reveal about the players’ cards.