The articles in this symposium issue demonstrate the problems and potential in the use of custom in modern legal systems. Marie Kim describes South Korea's struggles to fit custom, both age-old and possibly recently invented, into a modern constitutional structure. Professors Modéer and 0rebech detail the different directions Eastern and Western Scandinavian countries have taken, with Sweden showing more tolerance for custom in its property law and treatment of the Sàmi and Norway adhering to a code-based system that only begrudgingly allows custom to sneak in at the margins. One of those margins in Europe, as Pascale Fournier and Pascal McDougall's Article demonstrates, is the family law customs of Jewish and Muslim minorities in Germany, an issue that will likely prove a continuing challenge to the civil law systems of Europe. Professor Kostritsky undertakes an extensive survey of the various ways in which law and economics adherents use and try to define norms, a form of custom that has emerged from the shadows to prove that custom has not completely disappeared even in our heavily regulated and legalized society. By contrast, Henry Smith suggests that the age of custom is largely over in American law, at least in the field of property, because custom can only function within relatively small communities and cannot provide generalizable rules of law. Finally, Professor Schauer offers Hartian insight into the perennially difficult question of how to define custom, a problem with which jurists have been struggling since at least the twelfth century.
Despite the current flood of interest in bottom-up lawmaking that these articles represent, custom is preeminently pre-modern law-law before the common use of legislation, before the sovereign nation-state.1 And if the medieval jurists peered over our shoulders they would, I suspect, conclude that lawyers today do not quite understand how custom works.
This should come as no real surprise. The jurists of the medieval and early modern periods lived in a world saturated with customs that formed many, even most, of the legally-enforceable rules of decision governing their lives and their society.2 They had to try to understand it. We live in a world in which custom is something of a novelty and in which we instinctively hold positivist notions about the sources and nature of law. Wrapping our modern minds around pre-modern custom would require putting aside notions of law that have had two or three hundred years to take hold. But if we were to try, we might find that the medieval jurists have something valuable to teach us about custom and how we currently use the concept.
First, and perhaps most importantly, studying the writings of the Roman and canon law jurists of Europe between the twelfth and seventeenth centuries would reassure us that our confusion about custom is not new. Both then and now, legal scholars have begun with a definition of custom that derives ultimately from the Romans and contains two parts: an objective requirement that an act be done repeatedly over time, and a subjective requirement that the people engaging in the act do so out of a sense of legal obligation, what has since the nineteenth century been called the opinio juris/
Looking at the way the jurists treated this definition of custom, we might realize that, despite sharing the same definition with them, we do not have quite the same respect for it. Because they defined custom as a form of law, the jurists understood that not every behavior, no matter how longstanding or binding, deserved to be denominated a custom. As a consequence, they created elaborate distinctions dividing custom (repeat behavior binding the whole relevant community due to the "people's will or their tacit consent")4 from other categories." They drew the first distinction between mere longstanding practices (usus or mos) and custom. The former lacked the requisite opinio juris. Custom required both usus and the sense of being bound. …