Exiting Custom: Analogies to Treaty Withdrawals
This Essay, a contribution to a symposium on Withdrawing from Customary International Law published in the Duke Journal of Comparative and International Law, analyzes the rules governing unilateral exit from multilateral treaties and considers the insights they offer for understanding how unilateral withdrawals from customary international law (CIL) might function in practice. Drawing upon my previous study of the design and use of treaty denunciation and withdrawal clauses, I argue that if the rules governing unilateral exit from CIL were to track those governing unilateral exit from treaties, states would be subject to a wide array of procedural and substantive constraints on their ability to exit from international laws they no longer intend to follow.
Part I reviews the procedural limitations on treaty denunciations, including the obligation to act in good faith, the requirement to provide reasonable notice of an intent to withdraw, and the possibility of offering a justification a state’s decision to quit a treaty. Part II analyzes the substantive constraints on treaty denunciations, including the presumption against partial exit and against withdrawals from treaties that contain no provisions governing denunciation or withdrawal. Part III analyzes the legal consequences of exit, including the withdrawing state’s continuing responsibility for violations that occurred before a denunciation or withdrawal takes effect. Part IV briefly concludes.