The Role of Consent and Uncertainty in the Formation of Customary International Law

While treaty norms only bind states that have explicitly consented to a treaty, the case is less clear with customary international law. According to the prevailing opinion in international law scholarship, states are not bound by a customary norm if they have persistently objected to the formation of the norm. This contribution will show that the concept of persistent objection cannot be consistently applied to all areas of international law. It proposes a classification of three different types of norms – norms protecting a common good, norms of coordination and norms related to ethical values. In each of these three fields, the considerations for whether states can be bound against their expressed will differ. In the case of common goods, state consent is perceived as an epistemological tool in order to cope with uncertainty. Dissent is, therefore, no compelling reason for a state not to be bound by a specific norm. Norms of coordination basically protect the expectations of other states, so that only such states are bound that do not explicitly object. The most difficult case is ethical norms, where states have a margin of discretion in balancing competing rights and interests, but cannot inhibit the validity of the norm through individual objection.