Identification as the Process to Determine the Content of Customary International Law

Scholars recently have been arguing that one can interpret rules of customary international law. This article argues that the case for the interpretability of custom is unpersuasive and that the content of customary rules is determined by the process to ascertain the existence of such rules, known as identification. The main thrust of this article is that state practice and opinio juris are central to determining the content of customary international law, but that the case for the interpretability of custom wrongly downplays that centrality. To develop its argument, this article discusses the overlap between content and existence of customary rules, the means to distinguish between putative customary rules (called ‘individuation’), the means to interpret customary rules and the possibility for customary rules to move between levels of abstraction without evidence of state practice or opinio juris (called ‘plasticity’). This article also criticises the legitimacy of interpreting customary international law.