Unravelling the Mystery of Jus Cogens in International Law

Abstract

Jus cogens is a mysterious body of international law. For decades, international lawyers have sought to answer a range of questions about jus cogens. Yet uncertainty persists. This essay makes a start in unravelling the mystery by addressing a basic question: how jus cogens is made, changed, or unmade. Prominent in existing explanations of jus cogens law-making is the idea of consent. Many attempts have been made to show that jus cogens is consensually made, or that it is not. I suggest that we should abandon consent-based explanations; consent is not a useful lens through which to analyse jus cogens law-making. At the same time, existing accounts which do reject consent are not persuasive either. I seek to show how we can more effectively explain jus cogens law-making without relying on the idea of consent. In essence, a rule of international law becomes jus cogens because it is believed by certain legal officials – principally states – to be morally paramount. These moral beliefs are social facts which go to the weight of the rule, with the consequence that the rule’s weight increases. Jus cogens rules are weighty rules in international law. This explanation of jus cogens law-making draws upon familiar insights in the philosophy of law, and circumvents the problems which trouble existing approaches.