Mandatory Versus Default Rules: How Can Customary International Law Be Improved?

Customary International Law (CIL) is plagued with uncertainties about its sources, its content, its manipulability, and its normative attractiveness. The rise of law-making through multilateral treaties also makes the proper role of CIL increasingly uncertain. This is an opportune time, therefore, to be thinking of ways to revive and improve CIL. In a prior article, we argued that the "Mandatory View" of CIL, pursuant to which nations are barred from ever withdrawing unilaterally from rules of CIL, is functionally problematic, at least when applied across the board to all of CIL. We also suggested that CIL might be improved by allowing for exit rights similar to those allowed for under treaty regimes, many of which allow nations to withdraw unilaterally, at least after giving advance notice of their intent to do so. In a series of papers in Yale Law Journal’s online edition, a number of scholars - Lea Brilmayer, William Dodge, David Luban, Carlos Vazquez, and Isaias Tesfalidet - take issue with our proposal of such a "Default View" of CIL. In this essay, we respond to their arguments, while also emphasizing the need for additional consideration of the ways in which CIL might be improved.