Legally binding custom is conventionally analyzed in terms of two independent elements: regularities of behavior (usus) and convictions of actors engaging in the behavior that it is legally required (opinio juris). This additive conception of custom is deeply flawed. This Essay argues that we must abandon the additive conception and replace it with an account of custom that understands legally relevant customs as norms that arise from discursive normative practices embedded in rich contexts of social interaction characterized by intermeshing anticipations and interconnected conduct. The hallmark of legally binding customs, it is argued, is not the addition of belief or conviction to behavior, but rather the integration of meaningful conduct into a web of legally recognized reasons and arguments.
Gerald J. Postema, Custom, Normative Practice, and the Law, 62 Duke LawJournal 707-738 (2012).
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