Duke Law School hosted a conference on “The Role of Opinio Juris in Customary International Law” on July 12 and 13, in Geneva, Switzerland. Held in conjunction with the Duke-Geneva Institute in Transnational Law, the conference brought together leading American and European scholars and practitioners. The topic of the conference overlapped with an ongoing project of the United Nations’ International Law Commission (ILC) concerning customary international law, and several members of the ILC participated as commentators and observers.
The conference, attended by more than 90 scholars, lawyers, and students, was organized by Curtis Bradley, the William Van Alstyne Professor of Law and Professor of Public Policy Studies, and was sponsored by Duke’s Center for International and Comparative Law.
Customary international law represents, along with treaties, a major source of international law, explained Bradley. “Customary international law is based on the unwritten practices and beliefs of nations. Most international lawyers would say that in order for a rule to be binding as a matter of custom there have to be widespread practices of states that support the custom. And then very significantly, most international lawyers would say that nations have to be following that custom ‘out of a sense of legal obligation,’ not just as a matter of habit or courtesy.” The sense that a custom is legally binding represents the concept of opinio juris, which came into widespread use within the last 100 years and remains open to interpretation.
“There are still a lot of questions about how opinio juris really works and about how it ever comes into being,” said Bradley, who is a Reporter on the American Law Institute's new Restatement project on the foreign relations law of the United States. “How do nations acquire a belief that something is legally binding? We explored a lot of puzzles at the conference and, I think, made some headway on them. These are problems that scholars of international law have been really wrestling with for 50 years at least — how opinio juris develops and how it works.”
In that regard, the conference afforded an exciting opportunity for scholars to engage in dialogue about how international law should work, said Bradley.
“Each panel was lively and interesting, and included a diverse range of perspectives. There was a good balance of prominent American and European scholars on the panels, who brought differing perspectives on international law,” he said. As a hub for international institutions, Geneva was a great place, he said, to get the dialogue started — and sustained informally over dinner with the speakers.
“There is interest among many of the participants in expanding the short papers that were posted online into book chapters that would appear in an edited volume, so I will explore that option going forward.”
Facilitating interaction with and assisting the ILC commissioners who are attempting to craft a statement of principles about how customary international law works, how and when it forms, and how it is evidenced was a key goal of the conference, said Bradley. “The task of the ILC is sort of an international analog to the American Law Institute’s Restatement project. It will require difficult drafting and consensus-building among lawyers from around the world who have different concepts of how the law works. I hope that our conference helped shed additional light on the topic of customary international law in a way that might ultimately help generate consensus.”
The International Law Commission planned to start discussing its special rapporteur’s first report on customary international law on July 17, making the Duke conference particularly timely, Bradley added. “The special rapporteur, Sir Michael Wood, attended and participated in the conference, and he reported that the discussions were very helpful for his work.”
The conference added a new dimension to Duke Law’s summer institute in Geneva for both faculty and students, many of whom attended the conference, Bradley said.
“We have these two great summer institutes in Geneva and Hong Kong for our students and students from around the world,” said Bradley, who just finished his portion of a course on Customary International Law in Theory and Practice at the 2013 Duke-Geneva Institute. “They have primarily been vehicles for teaching, with Duke faculty paired with an academic from another country in teaching many classes. The conference involved faculty in an additional aspect of what they normally do, which is engaging in scholarship as well as teaching.
“I think the students in my course who attended got a lot out of the conference,” he added. “They already had been reading materials addressing a number of the concepts that participants were discussing.”
“So I think the conference enriched the summer institute experience for everybody, and gave Duke Law a more substantial presence in Europe,” he said.
In addition to Bradley, Laurence Helfer, the Harry R. Chadwick, Sr., Professor of Law, Richard Schmalbeck, the Simpson Thacher & Bartlett Professor of Law and faculty director of the Duke-Geneva Institute, and Professor Mitu Gulati participated in the conference, addressing such matters as the history of customary international law (Bradley) and its relation to international tax law (Schmalbeck), treaties (Helfer), and how it is used by international courts (Gulati).
“This conference represented a good use of just some of the considerable expertise we have at Duke Law in the area of customary international law,” said Bradley, the author, most recently, of International Law in the U.S. Legal System, who has written extensively on the subject for 20 years, focusing primarily on its domestic role.
The conference was the latest in a series of initiatives at Duke focused on the role of custom in the law, including in the international arena. Notable among these is the Duke Project in Custom and Law, an interdisciplinary yearlong examination of what constitutes custom, how it evolves, who decides when norms have become custom, and what its relationship is to more formal sources of law. The project, which included a series of workshops and conferences, resulted in a symposium issue of the Duke Law Journal.
View conference schedule and papers for “The Role of Opinio Juris in Customary International Law” here.