The Relevance of Subsequent Agreement and Subsequent Practice for the Interpretation of Treaties

Abstract

In May 2012, the International Law Commission (ILC) appointed a special rapporteur, Georg Nolte, to complete a project on "subsequent agreements and subsequent practice in relation to the interpretation of treaties." Previously referred to by the name "treaties over time," the project is expected to result by 2016 in a series of "observations" or "conclusions" about how the meaning of a treaty might be determined based, at least in part, on the conduct of the States Parties after the treaty is concluded.

The project raises a large number of interesting issues, some of which concern terminology and line drawing, others that concern theory and history, and still others that concern when and how States and tribunals rely upon this phenomenon. This essay discusses the extent to which subsequent agreements and practice have actually been a relevant or important component of treaty law in the past and present, and what level of importance they might enjoy in the future. In other words, while there are certainly examples of the use of subsequent conduct in different fields of international law, how pervasive is this phenomenon, and is it increasing or decreasing in its relevance?

Keywords: Vienna Convention, treaty interpretation, subsequent agreement, subsequent practice