Customary International Law: A Moral Judgment-Based Account

Abstract

In this contribution to AJIL Unbound, I outline a moral judgment-based account (MJA) of customary inter-national law. On the MJA, moral judgment plays a dual role in the formation of customary international law. First, MJA is part of a disjunctive analysis of opinio juris, which involves a moral judgment about what the law ought to be or what it justifiably is. Second, the interpretive process of adducing a customary norm from state practice and opinio jurischaracteristically requires some moral judgment on the part of the interpreter. Along the way, I draw attention to two points at which the MJA departs significantly from the analysis presented in the International Law Commission (ILC)'s Second Report by Special Rapporteur Sir Michael Wood, on the identification of customary international law.1 First, by more sharply separating state practice from opinio juris, MJA avoids systematically double-counting the same facts as both opinio jurisand state practice. Second, MJA offers an effective response to the so-called paradox of custom, according to which a customary norm can only come into existence if a sufficient number of states mistakenly believe (or pretend to believe) that it already exists.