Concepts of Solidarity in the International Law of Obligations Moving beyond a One-sided Conceptualization of Solidarity

Concepts such as obligations erga omnes, interdependent obligations and jus cogens aim to clarify the implications of solidarity in international legal relationships for the (non-)performance of international obligations. Various scholarly accounts focus on the way in which these concepts have contributed to international law’s structural transformation towards greater solidarity and the effectuation of common interests in positive international law. This paper sheds new light on this familiar narrative. By proceeding from Hohfeld’s understanding of legal relations, it uncovers how existing concepts of solidarity focus solely on one side of international legal relationships, namely that of the right-holders. This has contributed to a preoccupation with optional solidarity in the international law of obligations; addressing the implications of solidarity for the circle of state(s) and/or international organizations(s) that are entitled to respond to an internationally wrongful act or material breach of treaty.

However, solidarity may also manifest itself amongst the duty-bearers in legal relations. In order to fully capture the legal implications of international law’s structural change towards cooperation and the pursuit of common interests, the international law of obligations is in need of concepts that further engage with this other side of legal relations. With this in mind, the paper introduces and explores the concept of shared obligations. The implications of solidarity amongst the bearers of obligations are not optional, but concern the performance of obligations, shared responsibility and the nature of the secondary obligations of cessation and reparation that may arise as a result of such responsibility.