Proving Customary Norms
Ontology and Evidence in International Law
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Abstract
This article addresses the epistemological and conceptual challenges involved in proving the existence of customary norms in international law. It argues that confusion surrounding usus and opinio juris stems from a failure to distinguish between the ontology of customary norms and the determination of their existence. Drawing on legal epistemology and social theory, the paper conceptualizes customary norms as products of socially constituted structures grounded in shared expectations. On this account, it is not required to prove that States regard their conduct as legally mandatory, but rather that second-order normative expectations are manifested through patterns of practice. Methodologically, the article defends a dual inferential model: inductive reasoning to establish practice (usus), complemented by abductive reasoning to infer the existence of shared normative expectations (opinio juris). It proposes narrative reconstruction as an appropriate evidentiary method and makes observations on the standard of proof required for customary international law.
Keywords
Legal epistemology, social normsDownloads
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DOI
https://doi.org/10.33115/udg_bib/qf.i11.23272Published
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