Helfer & Wuerth: An Instrument Choice Perspective on Customary International Law

Laurence R. Helfer (Duke Univ. - Law) & Ingrid B. Wuerth (Vanderbilt Univ. - Law) have posted An Instrument Choice Perspective on Customary International Law (Michigan Journal of International Law, forthcoming). Here's the abstract:

Contemporary international lawmaking is characterized by a rapid growth of “soft law” instruments. Interdisciplinary studies have followed suit, purporting to frame the key question states face as a choice between soft and “hard” law. But this literature focuses on only one form of hard law — treaties — and cooperation through formal institutions. Customary international law (CIL) is barely mentioned. Other scholars dismiss CIL as increasingly irrelevant or even obsolete. Entirely missing from these debates is any consideration of whether and when states might prefer custom over treaties or soft law.

This article applies an instrument choice perspective to demonstrate custom’s continuing relevance to contemporary international lawmaking. First, we use instrument choice to identify the distinctive design features that distinguish CIL from treaties and soft law. As an ideal-type, we argue, custom is a non-negotiated, unwritten and universal form of cooperation. Second, instrument choice illuminates the constraints that limit custom to particular types of cooperation problems, which we label as custom’s “domains.” Specifically, CIL’s design features limit custom to situations in which all-states-benefit from a norm, hegemonic custom, and normative custom. Third, an instrument choice approach predicts that states will continue to prefer custom over treaties and soft law when its design features or substance offer competitive advantages over international agreements and nonbinding norms. Our instrument choice analysis thus not only predicts when custom will form, it also helps to explain several doctrinal features of custom that have long troubled scholars.