The Notion of ‘Agreement’

Abstract

Chapter 8 is dedicated to the normative heart of subsequent practice, namely the notion of ‘agreement’. A single instance of practice and even an accumulated body of practice do not, in themselves, satisfy the requirements under article 31(3)(b) VCLT. To acquire the status of a primary means of interpretation, subsequent practice in the application of the treaty must be capable of establishing the agreement of all parties regarding the treaties’ interpretation. Unlike under article 31(3)(a) VCLT, the parties’ agreement under article 31(3)(b) VCLT is not manifest. The interpreter therefore needs to assess all potentially relevant practice to determine whether this practice, taken as a whole, actually establishes the parties’ agreement. This additional intellectual operation is not a dispensable add-on. It is, on the contrary, the sine qua non that justifies the status of subsequent practice as a primary means of interpretation by linking it to the agreement of the parties as the true masters of the treaty.