A Default Rule Theory of International Custom

William J. Moon, Yale Law School


This Essay develops a theory conceptualizing customary international law (CIL) as default rules of international law. In addition to challenging the predominant scholarly objection to CIL, it offers a unique perspective to the ongoing debate about its status under American law. The prevailing literature has split between the modern view and the revisionist view. The former understands CIL as self-executing federal common law, while the latter treats it as an optional source of law principally administered by states. The default rule view offers a third way: CIL is federal common law that can be repudiated through treaties or unilateral withdrawal.