Customary international law and the place of normative considerations

A large part of the theory of customary international law subscribes to the idea that we can determine the content of international custom by attending to certain social facts about the behaviour and intentions or beliefs of international agents. I argue that this idea is mistaken insofar as it excludes from the determinants of customary legal content the only considerations that could explain which social facts are significant, by how much, and which propositions of law they support: normative considerations.