- Rules of treaty interpretation — Vienna Convention on the Law of Treaties — Permanent Court of International Justice (PCIJ)
The Vienna Convention on the Law of Treaties of 1969 established a distinct hierarchy between the general rule of interpretation and supplementary means. Article 32 of the Convention subordinates the use of supplementary means to various assumptions connected with the outcome of the interpretation made on the basis of the general rule contained in Article 31. The list of the supplementary means laid down in Article 32 is not exhaustive and the Vienna Convention says nothing about the concept of preparatory works, of circumstances surrounding the conclusion of the treaty, and about the concept of other supplementary means of interpretation. These and other critical observations can be resolved by reference to indications from the comments of the International Law Commission and from international case law. The rule established in Article 32 can be considered to correspond to the international custom. The use of supplementary means of interpretation is important when the application of the general rule leaves the meaning ambiguous, obscure, or absurd. Recent international case law appears to illustrate the reasons that can lead the interpreter to find, in the supplementary means, a confirmation of the meaning emerging from the application of the general rule expressed in Article 31.