The Customary International Law Game

Abstract

Customary international law (CIL) is under attack as behaviorally epiphenomenal and doctrinally incoherent. In this article, we reject both claims. To be sure, CIL is a feat of levitation; it rests not on a rock-solid natural law basis of divine principles, but on a fabric of rational acts, woven through a multiplicity of relations over time. And while there are limits on, and variations in, the effectiveness of CIL, we argue that there are circumstances where it may independently affect the behavior of states. There is no reason in theory, or in data adduced by others, to believe CIL to be generally epiphenomenal. Since certain components of CIL serve as the foundation of all international law, this article suggests the circumstances under which one would expect international law to affect state behavior.