How Customary Is Customary International Law?

By Kadens, Emily; Young, Ernest A. | William and Mary Law Review, February 2013 | Go to article overview
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How Customary Is Customary International Law?

Kadens, Emily, Young, Ernest A., William and Mary Law Review


    A. Practice and the Extra Ingredient
    B. The Theory and Practice of Custom
    C. Customary Law and Contemporary
       Human Rights


The ambiguity of the lawmaker has long been a central problem in international law. Writing in the positivist tradition, H.L.A. Hart famously doubted that international law is law at all because it lacks not only a single sovereign lawmaker but also a system of "secondary rules" for the making and alteration of legal norms. (1) Treaties bind by consent, but only between the parties. Even when large majorities of countries sign on to multilateral agreements, we often lack any authoritative method for determining those agreements' meaning or guaranteeing consistent enforcement. In any event, treaty law leaves large gaps, (2) and often those gaps exist in those areas with the most pressing need for law. In an earlier age, international lawyers frequently turned to natural law to fill these gaps, (3) but a revival of the natural law tradition seems unlikely at a time when countries with widely varying religious, philosophical, and political traditions aspire to agree on one international law. (4)

Enter custom--the only form of law without a lawmaker still recognized in our post-lapsarian world. At certain times and places in world history, custom is thought to have given rise to a coherent and effective set of legal norms "from the bottom up"--that is, without the command of a single sovereign. (5) If merchants operating across state borders over time can produce a set of customary rules to govern their transactions, even without formal consent or the intervention of a sovereign authority, (6) then perhaps independent nations similarly can derive binding norms of conduct from their own practices. Conventional wisdom in international law thus holds that the international community has developed a set of definable rules through custom that nations must accept as law. (7) This wisdom rests on extrapolation from the historical success of custom in commercial law. On this view, customary international law derives its appeal not only from a fear that it may be the only game in town but also from a widely held sense that it is, well, customary.

We question that latter assumption in this Article by comparing early theories of custom with the debates in which publicists engage today. Article 38(1)(b) of the Statute of the International Court of Justice asserts that custom, defined as "evidence of a general practice accepted as law," forms a fundamental part of international law. (8) This assumption about the role of custom has a well-known history extending back to the writings of the Spanish theologian Francisco Suarez (1548-1617), who equated the law of nations with custom in his Treatise on Laws and God the Lawgiver of 1613. (9) This history, however, has a prehistory that modern scholars do not know as well, and that prehistory sheds some interesting light on current debates about the usefulness of the standard definition of custom. The value of studying history lies not in any claim that premodern jurists had better answers than do scholars today, but rather in a historical perspective on the problem of how custom functions as law. That problem, then as now, remains largely intractable. The debates among jurists of the thirteenth and fourteenth centuries mirror the debates in which their intellectual descendants engage hundreds of years later. The story of custom, in both its past and present manifestations, thus underscores contemporary doubts about the usefulness of customary law on the international plane. Part I of this Article surveys the historical development of customary law. Part II ventures some suggestions as to what that history can tell us about current debates over customary international law.

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How Customary Is Customary International Law?


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