A Disaggregative View of Customary International Law-Making

This article argues that some familiar principles, like the protection of reasonable expectations or fair play, can justify the normative force and binding character of some types of customary international practices. We have no reason to think that any one of those principles can justify all customary practices that are typically taken to have such force. Accordingly, instead of proposing a unifying justification for all customary international law-making, I will suggest that the impact of past international practices on the normative situation of international agents is determined not by one master principle, but by a range of different normative principles, each applicable in different situations. If this is correct, i.e., if the principles that give customary practices their normative force vary depending on the kind of principle governing the practical problem that those practices are meant to respond to, both the critique and the defence of customary law-making must proceed on what I will call a ‘disaggregative’ basis.