Implying rights and obligations that are not explicitly set forth in a treaty is not a technique of treaty interpretation explicitly recognized in the Vienna Convention. But the practice of treaty interpretation supplies numerous examples of interpretively implied consequences of express treaty commitments. This chapter focuses on some of the best-known examples of treaty interpretation based on necessary implications ranging from the theory of implied powers of international organizations to the doctrine of positive obligations in international human rights law. Building on philosopher Robert Brandom’s theory of inferentialism, it argues that what is presented as necessary implications in treaty interpretation are discursively articulated inferential consequences of formal commitments undertaken under the treaty.

The author examines the place of consent in treaty interpretation at the time of the marginalization of the role of the intention of the parties. Whether the characterization of international law as a legal system grounded in State consent has ever been empirically true is, as he argues, open to discussion. For him, the law of treaties, however, is commonly seen as ‘a bastion of consensualism’. This sense of confidence has, however, never sat easily with treaty interpretation. The author claims that, despite the lip service sometimes paid to the fiction of the common intention of the parties, the official doctrine of treaty interpretation rests on the primacy of the terms of the treaty.