From Abundance to Indeterminacy: The Precautionary Principle and Its Two Camps of Custom

The question of what status the precautionary principle enjoys in international law has once again reared its head, most recently in the Indus Waters Treaty dispute between India and Pakistan before the Permanent Court of Arbitration. This article assesses the current state of play in respect of the precautionary principle and its status in international law. It identifies what it terms the two camps of custom - the custom camp and the no-custom camp - which find themselves on opposing sides in the debate. The article argues that the two camps are equally guilty of misunderstanding the precautionary principle and the nature of customary international law, though for different reasons. In so doing, the article shows that one side is guilty of 'precaution spotting', whereas the other ignores the implications of the 'rule v. standard' dialectic. These two concepts help us to understand the different claims advanced by the two camps. They also alert us to the fact that it is possible to conceptualize customary international law along two separate lines of inquiry: one lending emphasis to state practice and one relying on statements and declarations of rules. In pursuing these arguments, the article compares the precautionary principle with (other) norms of customary law, such as the 'no-harm rule' and the rules on cross-border environmental impact assessment, and argues that customary international law is best understood if we come to accept that there are multiple ways of identifying customary international rules.