Causal Loops, Ontological Crises, and Customary International Law
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Causal Loops, Ontological Crises, and Customary International Law
German Yearbook of International Law, Online First : pp. 1–30 | First published online: June 26, 2025
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Dr. Henrique Marcos, Lecturer in Law, Faculty of Law, European School, Maastricht University, Bouillonstraat 1-3, 6211 LH Maastricht, the Netherlands
Abstract
Abstract: For a norm of customary law to exist, a group of legal subjects must believe that it imposes an obligation to perform a specific action. Yet, until such a norm emerges, no obligation can arise. If the norm does not exist, it cannot impose any obligation, and so the subjects are not obligated. Without obligation, there can be no customary norm. This causal loop leads to an ontological crisis in international law: customary law should not exist, and yet it apparently does. This article examines two explanations for the origin of customary law. The first, the error thesis, argues that the initial belief in obligation is mistaken. The second, the biconditional thesis, suggests that customary law and legitimate expectations are co-constitutive, each depending on the other for existence. Drawing on research in social ontology, the biconditional thesis reinterprets the relationship between the collective recognition of legal subjects, the social world, and international norms.