Derogation and Defeasibility in International Law

In this chapter, we discuss the way in which implicit exceptions operate in the context of international law, with special reference to peremptory norms of general international law (i.e. jus cogens). To do so, we develop a theoretical model of exceptions based upon the notion of normative conflict. This model allows us to explain the relationship between derogation and defeasibility of peremptory norms of general international law. The chapter is organized in three parts. We begin by explaining the difference between explicit and implicit exceptions in light of the way in which different types of norms may conflict (section 1). We then consider the existence of explicit and implicit exceptions in international law vis-à-vis the existence of peremptory norms of general international law, which are by definition non-derogable (section 2). Finally, we employ our theoretical model—illustrated in section 1—to analyse Article 53 of the Vienna Convention on the Law of Treaties 1969, arguing that, in relation to jus cogens, the idea of non-derogation should be understood as referring to implicit and not explicit exceptions (section 3).