Subsequent Agreements and Practice: The Battle over Interpretative Power

Subsequent agreements and practices are important mechanisms by which treaty parties can assert their continued interpretive authority over treaties without having to amend those treaties. However, when states delegate power to international courts and tribunals to resolve disputes, they also delegate some interpretive authority to these judicial bodies. This delegation is typically implied and partial rather than express and exclusive. As a result, the claim of treaty parties to interpretive authority over their treaties exists in tension with the claim of international courts and tribunals to interpretive authority over the same treaties. In this Chapter, I argue that fights over the relevance of subsequent agreements and practice of the treaty parties before international courts and tribunals should be understood as representing a battle over interpretive power. On one level, this battle results in a dialogue between treaty parties and international courts and tribunals over the proper interpretation of those treaties. On another level, it represents a power play between two rival sources of interpretive authority that exist in tension with one anothe