Custom, Normative Practice, and the Law

By Postema, Gerald J. | Duke Law Journal, December 2012 | Go to article overview
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Custom, Normative Practice, and the Law

Postema, Gerald J., Duke Law Journal


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.


  I. The Additive Conception of Custom
 II. Against Addition
III. Integration, Not Addition: A Normative Practice Analysis
     of Custom
     A. Custom's Complexity
     B. Custom as a Normative Practice
     C. Discursive Normative Practices
 IV. Customary Law
     A. What Makes Custom Law? The Generic Question
     B. What Makes a Custom a Law? The Specific Question


Customs, social rules, and conventions are pervasive in our lives. They guide our actions as we navigate complex interactions of social life; they give social significance to the material things that often mediate those relations; and, even more, they define horizons within which actions we conceive and deliberatively entertain actions we undertake. Moreover, for millennia custom has been regarded as an important kind, or source, or ground of law. Although its importance has seemed to decline in modern legal systems, it is often not far below the surface in important parts of municipal law, and it is still thought to play an indispensable role in international law.

An analysis that breaks custom into an external element--regularities of behavior (usus)--and an internal element--convictions of custom followers that behavior conforming to the regularities is legally required (opinio juris)--has been nearly irresistible to theorists of law and of custom generally. What is more natural than to think that custom is a matter of consistent patterns of behavior observable from the outside plus some interior state like belief, attitude, or conviction, which turns patterns of behavior into norms for behavior? Yet, this additive conception of custom, despite its dominance, is deeply flawed, if not incoherent. Many of its problems are frequently rehearsed and recognized, and then almost immediately ignored. The jurisprudence of custom has long been in the grip of a kind of additive addiction, fed by the irresistible naturalness of its approach and the absence of any plausible alternative.

The project of this Essay is to sketch such an alternative, an integrated account that proposes to understand legally relevant customs as embedded in and arising from discursive normative practices. Inspiring this alternative approach is a brief sketch of custom by an ancient sophist turned stoic, which provides a useful foil for a terse characterization of the additive conception. (It also provides evidence that the additive conception is not completely irresistible.) I then seek to break the addiction to this conception in three steps. First, I briefly show how the "outside" versus "inside" trope that dominates thinking about custom beguiles theorists into an uncritical adoption of the additive conception. Second, I argue that this conception is bedeviled by problems deeper than the paradoxes and uncertainties widely, if uncomfortably, acknowledged in the jurisprudence of custom. Finally, I articulate and defend an alternative conception, the normative practice account. For this purpose, I focus on three core concepts and the interrelationships between them: normative practice, reciprocally oriented conduct, and discursive interaction.

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