This chapter examines the process whereby the concept of jus cogens was introduced into international law during the 1968–69 Vienna Conference on the Law of Treaties. The 1969 Vienna Convention on the Law of Treaties, the conference’s final product, declared that some rules of international law command universal authority, with Article 53 recognizing ‘peremptory norms of general international law’ (without specifying which norms counted as such). Yet the negotiations through which jus cogens entered into the law of treaties were marked by wide-ranging debates about the nature and limits of the treaty-making power, and ultimately about the basic structure and orientation of international law more generally. On the one hand were lawyers and diplomats from socialist and nonaligned states for whom the concept was potentially useful as a means of undercutting the legality of unequal treaties, colonial concession agreements, and other substantively unjust instruments. On the other hand were lawyers and diplomats from industrialized countries who were committed to the traditional principle of pacta sunt servanda—the ‘sanctity of compacts’—and deeply skeptical of any attempt to introduce a normative spectrum in which a select group of rules would have controlling authority over all others.

As a doctrine of positive international law, jus cogens superveniens gives juridical effect to the natural law’s prohibition of conduct violative of aspects of the transnational common good that reflect absolute human rights. In order to be fully valid in the sense that it commands a moral obligation of compliance, a measure for regulating the life of a community must be reasonable. A measure cannot be reasonable if its purpose is not the preservation or enhancement of the common good. The common good is the full array of physical, cultural, and institutional arrangements that facilitate the ability of persons in their various communities, including the transnational community, to advance their human flourishing. Human rights are conclusions of practical reason that always constitute essential aspects of the common good. Some human rights are ‘absolute’ in that they are not subject to limitation or restriction on any grounds, because any such limitation or restriction can do nothing but damage the common good. Although natural law is binding in reason, the positive law and other juridical measures of official authority are frequently required to effectively serve the common good.

EU law has a complex relationship with the concept of peremptory norms. On the one hand, the case law of the ECJ shows a pattern of ‘avoidance’ of peremptory norms of general international law, namely a reluctance by this Court to consider the legal effects of such norms in cases where they may be relevant. This is clear in the Kadi and Front Polisario/Western Sahara sagas. On the other hand, EU law has ‘assimilated’ the concept of peremptory norms more than it may seem at first sight. Indeed, it may be affirmed that EU law has its own system of peremptory norms. Such as system is based on norms and principles that have some of the defining features of the peremptory norms of general international law (including a system of enhanced responsibility for serious breaches of such peremptory norms). While, in analytical terms, this characterization does not matter much for EU law, it is certainly critical to the proposition that general international law does not exclude the existence of a regional jus cogens.

The author concludes the volume by reflecting on the interface between philosophy and law, arguing that they are both complementary and interdependent. He shows examples of the legal translation of philosophical principles and stresses the necessity to establish a system of responsibility – that is, a clear system of sanctions – so that philosophical and legal norms do not remain mere gratuitous statements. The chapter reflects on the philosophical foundations of legal responsibility, the historical movement of gradual individualization of responsibility and the shift to joint obligation to respond to collective threats and challenges. It ultimately argues that classical responsibility reduced to an essentially inter-individual relationship is technically very sophisticated, both philosophically and legally, but insufficient to face collective challenges (in particular the environmental crisis).

Throughout the years, various legal concepts have emerged that recognize that more than two states (in the form of one duty-bearer and one right-holder) may be involved when it comes to the performance of an international obligation, and that this can have relevant implications for treaty and responsibility relations. In this respect one may think of concepts such as obligations erga omnes, interdependent obligations and jus cogens. This chapter explores and analyses the way in which the international law of obligations, through these concepts, has addressed legal relations that involve more than simply one duty-bearer and one right-holder. By doing so, the chapter aims to illustrate the limits but also the B1:L9