The Role of Domestic Courts in the Interpretation of Customary International Law: How Can We Learn From Domestic Interpretive Practices?

Abstract

This paper examines the contribution that domestic courts may have in the development of rules or guidelines for the interpretation of CIL. The examination is motivated by three considerations. Firstly, unlike in the case of treaties whose interpretation is guided by Art. 31 of the Vienna Convention on the Law of Treaties (VCLT) and its customary counterparts, presently we do not have clear rules or guidelines for the interpretation of CIL. In fact, legal scholarship is currently still discussing whether custom as a source of law can be subject to interpretation, and if so, what are apposite methods for its interpretation. While at present little is certain, it has been argued persuasively that custom and treaties cannot always be subject to the same methods of interpretation. Thus, we cannot just transplant the methodology of treaty interpretation onto custom wholesale, and it might even be the case that custom requires a methodology all of its own. Secondly, scholarship on the role of domestic courts in the development of international law has persuasively demonstrated that domestic courts can contribute to international law both formally and informally, especially in areas where there are lacunae or the law is yet to be developed. Thus, the practice of domestic courts with respect to the interpretation of custom may prove a valuable source in our study and understanding of this developing field. Finally, because by turning to domestic courts we open the door to a wealth of cases which can provide us with examples and insight into the interpretation of custom. Depending on the legal system in place, domestic courts may be faced with the task of interpreting not only CIL but also domestic custom. Thus, domestic courts may be uniquely positioned to provide insight into the methodology of interpreting custom as a source of law. This paper examines the interpretation of custom by domestic courts in a handful of cases, and makes some preliminary observations based on them.