International treaties often reflect long-term agreements that are difficult to amend. For instance, we see the difficulty associated with amending the United Nations Charter, despite longstanding calls for institutional reform. We also see the stalemate with the Doha Round of trade negotiations, where disagreements between developed and developing countries have prevented amendment to WTO obligations to further reduce trade barriers. It is in this context that I suggest we look to treaty interpretation tools to adapt treaties to evolving circumstances. In particular, the conduct of treaty parties subsequent to the conclusion of a treaty allows an interpreter to gauge how the parties intend to apply treaty obligations to changing times and circumstances. My remarks address (1) the framework for interpreting treaties; (2) how treaty interpretation can be used to adopt an evolved interpretation of treaty terms; and (3) the distinction between an evolved treaty interpretation and treaty modification.
FRAMEWORK FOR TREATY INTERPRETATION
It is generally accepted that Articles 31-33 of the Vienna Convention reflect customary principles of treaty interpretation. Article 31(1) requires interpretation to be undertaken in good faith, in accordance with the ordinary meaning of the treaty terms in their context and in light of their object and purpose. Article 31(2) defines in further detail the meaning of "context." Article 31(3) requires that "together with the context" the interpreter take into account
(a) any subsequent agreement between the parties regarding the interpretation of the treaty or the application of its provisions; (b) any subsequent practice in the application of the treaty which establishes the agreement of the parties regarding its interpretation;
(c) any relevant rules of international law applicable in the relations between the parties.
Within Article 31 there is no interpretative hierarchy. It was envisioned by the International Law Commission (ILC) that "the application of the means of interpretation in the article would be a single combined operation. All the various elements, as they were present in any given case, would be thrown into the crucible, and their interaction would give the legally relevant interpretation." (1)
Of the provisions mentioned above, Articles 31(3)(a) and (b), in particular, offer the possibility to adopt an evolved interpretation of treaty terms. Both articles require an interpreter to take into account the subsequent conduct of treaty parties where such conduct demonstrates an agreement as to the interpretation of treaty terms. In this regard, the distinction between Articles 31(3)(a) and (b) is more formalistic than substantive. A formal written agreement between the parties agreeing to the meaning of an otherwise ambiguous term would likely fall within Article 31(3)(a). On the other hand, independent actions of both parties, temporally separated, that appear to demonstrate agreement between them on the meaning of the treaty are more likely to come within Article 31(3)(b). There is a spectrum of conduct between these two, and in this regard, Articles 31(3)(a) and (b) can be seen to be on a continuum, with the former requiring a higher evidentiary threshold. (2) That continuum also represents the weight to be accorded to the party agreement for the purposes of treaty interpretation. The stronger the case for the conduct to come within Article 31(3)(a), the more weight that should be given to the conduct as expressing an authentic interpretation of the text.
EVOLUTIVE APPROACH TO TREATY INTERPRETATION
Are there any boundaries to the parties' ability to agree to an evolved interpretation of treaty terms? In his work on the subject with the ILC, Professor Georg Nolte has noted that treaties can "change over time," "must adapt to new situations," and "evolve according to the social needs of the international community. …