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Custom, Normative Practice, and the Law

32 Pages Posted: 16 Jul 2013  

Gerald J. Postema

University of North Carolina - Philosophy and Law

Date Written: November 1, 2012


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 behavioral regularities, but rather the integration of meaningful conduct into a web of legally recognized reasons and arguments.

Keywords: Custom, Normative Practice, opinio juris, international law, social interaction

JEL Classification: Z 00

Suggested Citation

Postema, Gerald J., Custom, Normative Practice, and the Law (November 1, 2012). Duke Law Journal, Vol. 62, No. 707, 2012; UNC Legal Studies Research Paper No. 2294081. Available at SSRN: or

Gerald J. Postema (Contact Author)

University of North Carolina - Philosophy and Law ( email )

Van Hecke-Wettach Hall, 160 Ridge Road
CB #3380
Chapel Hill, NC 27599-3380
United States

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