[Joost Pauwelyn is Professor of International Law at the Graduate Institute of International and Development Studies in Geneva and Manfred Elsig is Associate Professor of International Relations and Deputy Managing Director of the World Trade Institute of the University of Bern.]
In principle, the Vienna Convention rules on treaty interpretation apply equally to all treaties and all international tribunals. In practice, however, we observe a wide variation in methods and choices of treaty interpretation: across tribunals, in different policy areas, and even before the same tribunal looked at over time.
The international relations (IR) literature has largely overlooked the factors that explain the extent and scope of treaty interpretation. Although 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 behavior across international tribunals. This chapter tries to fill this gap by providing a conceptual toolkit inspired by IL and IR theories to approach (i) the various types of “interpretation choices” (we describe five such choices, see table below) and (ii) underlying factors that may drive or explain these choices, distinguishing between factors related to “demand-side interpretation space” and “supply-side interpretation incentives”. We provide illustrative examples to tease out our explanatory framework looking at a variety of tribunals (ICJ, ICC, ICTY, ECtHR, GATT/WTO, ECJ etc.) but do not engage in proper empirical testing.
As to the importance of treaty interpretation, two caveats apply. First, our claim is not that treaty interpretation is always the crucial factor in the outcome of disputes. In some cases, the tribunal’s establishment of the facts rather than the law is more important. Second, although we believe that a tribunal’s stated method of interpretation influences outcomes (especially where a court’s discretion is bound by a particular method selected by earlier courts), we do acknowledge that, in some cases, a tribunal’s interpretative method may be little more than an ex post justification or “façade” for an outcome reached on other grounds. (Table 1)
We suggest that variation of interpretative methods across tribunals is not randomly distributed. We realize that the factors we list here are not exhaustive and sometimes overlap. Still, we believe that the framework captures the essential drivers and offers a useful way to distinguish between them. The choice of interpretation (or the mix) is a result of the interaction of two variables: “interpretation space” (largely determined by treaty negotiators or principals setting up the tribunal) and “interpretation incentives” (experienced mainly by the judges on international tribunals). (Table 2)
Interpretation space (the demand side) is defined by the degree of contract completeness and oversight of principals. We conjecture that the greater the incompleteness and the more difficult for principals to collectively act the greater this space within which international tribunals can (or have discretion/freedom to) act.
Interpretation incentives (the supply side) are a result of institutional features and guiding norms that differ from one tribunal to the other. As to institutional features we discuss a tribunal’s lifespan, the composition of its constituency, and institutional competition. As to norms, three factors influence the supply side of interpretation: legitimacy, interpretative community, and legal tradition.
In summary, we argue that the greater the interpretation space the more likely tribunals are to use expansive interpretation strategies. This should be reflected in particular in teleological, evolutionary, and gap-filling interpretation techniques. However, this interpretation space interacts with a crucial second factor: a tribunal’s motivation (interpretation incentives). Having the space to engage in expansive interpretation strategies not always leads to such strategies: space is a necessary but not a sufficient condition and how this space is filled out depends on interpretation incentives. We have listed institutional factors and norm-type factors that condition a tribunal’s motivation. These supply-side incentives may, in turn, steer the tribunal toward more or less expansive strategies. At this stage, we only provide examples to illustrate our framework. The next step would be to explore in greater detail the interaction effects between interpretation space and interpretation incentives to offer more specific hypotheses to be tested empirically.