Customary International Law: Interpretation from Beginning to End

Abstract

Abstract Does interpretation have a role to play with respect to customary international law? Common wisdom suggests that, because customary legal norms are unwritten, they need not be interpreted prior to their application. Instead, it is assumed that once one has identified such a norm, one also knows its content. This approach glosses over a series of critical questions: what interpretative choices are made when describing the practice leading to the formation of legal norm in a certain way as opposed to another? What choices are made when interpreting a given practice so as to infer norms of a general import? And what leeway is then left for interpreting norms already identified so as to clarify their meaning? Tackling these questions, this article argues that interpretation in fact can play a role at every stage in the life of custom. As such, interpretation calls us to rethink our operating assumptions about this fundamental source of international law by putting front and centre two neglected theoretical problems: custom’s inherent plasticity and the difficulty of clearly individuating its legal rules.