How customary is customary international law?

• Author: Kadens, Emily

TABLE OF CONTENTS INTRODUCTION I. AN INTELLECTUAL GENEALOGY II. THE HISTORY OF CUSTOM AND CURRENT DEBATES ABOUT CUSTOMARY INTERNATIONAL LAW A. Practice and the Extra Ingredient B. The Theory and Practice of Custom C. Customary Law and Contemporary Human Rights CONCLUSION INTRODUCTION

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.

1. AN INTELLECTUAL GENEALOGY

   Following the parameters laid down in Roman law, (10) the medieval jurists believed that custom consisted of acts, repeated with some degree of frequency over some period of time, that the community--or some part thereof--understood itself to be obligated to continue performing due to its tacitus consensus, a phrase usually translated as "tacit consent." (11) Scholars of customary international law today begin, whether in support or opposition, from nearly identical premises. (12)

   Nearly, that is, but not quite identical, for modern publicists generally use the principles of state action plus opinio iuris (the sense of being bound) to define custom. (13) Some publicists have claimed that the nineteenth-century replacement of tacit consent with opinio iuris represented a distinct caesura with a premodern approach of lesser sophistication and usefulness. (14) The older so-called consent theory suggested a sort of contractual basis to custom. The medieval jurists did sometimes describe the workings of custom in contractual language, speaking of tacitus consensus and asking, for example, whether all members of a community, including those lacking capacity to contract, had to give their consent. (15) But the Latin word consensus had subtler meanings than just "consent" in a purely contractual sense. One of the leading Latin dictionaries defines the word variously as "agreement, accordance, unanimity, [and] concord." (16) The jurists' discussions of custom make clear that they did not hold simplistic, contractual views of custom formation. In fact, modern scholars will hear in the voices of the medieval jurists much that will sound familiar.

   The medieval jurists recognized that humans engaged in many types of repeat behavior, not all of which rose to the level of custom as law. (17) Individuals acquired habits; family, social, or occupational groups developed preferred practices; courts and chanceries established styles, for instance for documents or procedures. None of these habits, usages, practices, or styles constituted customary law, despite the fact that in colloquial speech any of them might be referred to as a custom, (18) The jurists needed a way to distinguish mere nonbinding practices from binding customary law, and they found this in the interlocking criteria of duration, repetition, and tacitus consensus.

   Duration proved to be the least controversial issue, though not for lack of options. Custom was, by its nature, defined by tradition. As the great fourteenth-century Italian jurist Bartolus de Sassoferrato (1313-1357) wrote, "A statute obtains [its] consent expressly, and therefore does not require other conjectures [about its existence].

   But custom requires tacit [consent]. Therefore a long passage of time is necessary, so that [the custom] may become apparent through the consent of the people and their perseverance [in the act]." (19) Although some jurists initially thought that the duration requirement meant "since time immemorial," (20) and others argued for the canon law rules of forty years, the scholarly consensus soon coalesced around ten years (21) "provided that uniform and frequent acts occurred within this period." (22) A longer period, of course, made the existence of the custom more certain, but only a decade was needed. (23)

   Frequency of acts proved more difficult to pin down, but the requirement was important because the jurists saw repetition of behavior as a key indicator of tacitus consensus. (24) According to Bartolus, "[T]he people are not understood to have consented, unless the act occurs frequently." (25) How many times during a decade did an act have to be repeated in order for its repetition to establish the requisite consent? Certainly "as many concrete instances would have to be proved as would sufficiently indicate the tacit consent of the people." (26) The Ordinary Gloss, the authoritative commentary written in the margins around the texts of the Roman law and completed around 1230 by the Italian law professor Franciscus Accursius (c. 1182-1263), promoted the idea that "twice makes a custom," (27) but not everyone agreed. Some thought that when the Roman law text on which they were all commenting said "frequenter" it literally meant "frequently," and twice was not frequent. (28) On the other end of the spectrum, the thirteenth-century French law professor Jacques de Revigny (c. 1230-1296) effectively foresaw the concept of "instant custom" when he offered this hypothetical about the creation of the custom of primogenitor:

   Assume that the whole population of a city, or a majority of it, tacitly performs one act. We are at the beginning of the introduction of that custom by which the oldest son inherits everything. At a certain time, that whole city went to war. All or almost all the men were killed. On one day [their] sons adopt the usage that the oldest son takes everything, and thus the people, or a majority of them, have tacitly consented by one act. Is this legislation? Certainly not, because something becomes a statute by the means of express discussion among the community about what shall be law in the future. (29) As long as the community continued to maintain the usage of primogenitor, he said, then the single act introduced a custom. (80)

   But even if the jurists accepted the Gloss's maxim that "twice makes a custom," they fretted over how that corresponded to the duration requirement. For example, they argued over the custom-creating efficacy of the following situation: An act happens on day one, and is repeated the next day. Then ten years go by and the act is not repeated again, though no one has opposed it. Is there a custom? (31) Odofredus (d. 1265), who taught at the University of Bologna in the first half of the thirteenth century, wrote that his predecessors Johannes Bassianus (late twelfth century) and Azo Porcius (fl. 1150-1230) believed that such a scenario did introduce a custom. (32) But Odofredus's teacher, Jacobus Balduinus (d...