The Politics of Treaty Interpretation: Variations and Explanations Across International Tribunals

International tribunals rely on interpretation of legal texts as a crucial tool in adjudication. What is puzzling is the increasingly wide variation we observe in treaty interpretation by international tribunals across policy areas and over time. The international relations (IR) literature has largely overlooked the factors that explain the extent and scope of treaty interpretation. While there is an extensive normative literature in international law (IL) as to the right way to interpret, empirical work still lacks mid-range theories to account for the observed variance of behaviour across international tribunals. This chapter tries to fill this gap by providing a conceptual toolkit inspired by IL and IR theories to approach the various types of interpretation (interpretation choices) and underlying explanations (demand side interpretation space and supply side interpretation incentives).

In IL scholarship, attention has focused on the normative question of how treaties should be interpreted, especially with reference to the Vienna Convention on the Law of Treaties (VCLT) referring, in turn, to text, context, object and purpose and preparatory works of a treaty (Gardiner 2008; Van Damme 2009). These Vienna Convention rules apply, in principle, to all international tribunals irrespective of their institutional set-up, subject matter or geographical scope. Divergence between international tribunals in the practical application of these rules of treaty interpretation has been pointed out (Weiler 2010). Yet, categorizing where exactly international tribunals have diverged in their approach and, especially, thinking about what factors might explain these differences, has received little or no attention. Instead, divergence has been labelled as an incorrect application of the Vienna Convention rules or proof that these rules are outdated or should not fully apply to a particular tribunal (Klabbers 2010:33). This chapter leaves the normative issue aside and focuses on the descriptive and conceptual aspects: What is it that international tribunals actually do and how could this behaviour be explained, first, within the same tribunal operating over time and, second, across tribunals operating in different contexts or regimes?

In IR scholarship, increasing attention has been paid to the role of international tribunals (e.g. in the broader “legalization” debate or as agents vs. trustees) and to the design of dispute settlement mechanisms in international agreements (Koremenos 2007; Alter 2008a). Other studies have addressed the effects of proliferation of international tribunals and forum-shopping (Drezner 2006; Busch 2007). In addition, most of the commitment literature in IR focuses on the question why states sign or ratify international agreements and what factors explain the degree of implementation of or compliance with international agreements. Yet, what has been largely overlooked is the stage between commitment and compliance, more specifically, the process by which commitments are interpreted in the first place. While many actors in the realm of international politics may eventually influence the way treaty obligations are interpreted (in particular, treaty parties themselves), the key institutions (and usually the last resort) engaging in this process are increasingly international tribunals (Romano 2007). These tribunals are called upon to engage in an interpretation, precisely because member states or other actors that may have standing cannot agree among themselves on a way to read the commitments.

This chapter attempts to push the conceptual borders across both fields. After defining and discussing the increased importance of treaty interpretation (Part II), we first describe the five interpretation choices that international tribunals most commonly make (Part III). We then offer a framework that may explain these choices (Part IV). We provide illustrative examples to tease out our explanatory framework, but do not engage in proper empirical testing. At this stage, our goal is merely to demonstrate that tribunals have a varying degree of interpretation space within which they must select between different interpretative techniques. Understanding these techniques and the factors that may explain their adoption can, in turn, provide useful insights into the operation, role and optimal design of international tribunals.