A Sliding Scale Approach to Travaux in Treaty Interpretation: The Case of Investment Treaties

Materials produced during the negotiation of treaties, commonly called travaux préparatoires (travaux), are given formal significance as a supplementary means of treaty interpretation under article 32 of the Vienna Convention on the Law of Treaties (VCLT). Travaux present both risks and opportunities for treaty interpretation, and international adjudicators have differed in how they define the rationale for referring to travaux, how they use these materials, and even more fundamentally, what materials they classify as travaux. This article proposes a methodology to guide the more structured identification and use of travaux. Under the proposed sliding scale approach, treaty interpreters assess the utility of material to the interpretive exercise by reference to its precise qualitative features and the context of interpretation, rather than by categorizing materials as travaux or not. The article uses the interpretation of investment treaties in investor-state arbitration as a case study to illustrate the proposed approach and its utility. The discussion, including the proposed sliding scale approach, is nonetheless equally relevant for interpreting all manner of treaties.