Conceptions of custom in international law

Abstract

International legal theory has long relied on a concept of custom to explain one of the purported 'sources' of international law. That reliance, however, has been largely devoid of philosophical attention to the concept of custom itself, instead seeking to formalise the method through which 'non-legal' custom can be transformed into 'law'. This thesis advances the proposition that such an approach adopts an unnecessarily narrow view of the concept of custom, and results in the neglect of alternative paradigms of custom and their potential manifestations in international law. To consider the concept of custom in its own right, this study examines how custom has been conceived in philosophical analysis beyond the work of international legal theory. The results reveals not one but three conceptions of custom, concerned respectively with treating custom as a source of law; as a mode of rights independent or equal to law; and as a foundation of interaction from which law is generated. These contrasting paradigms of custom are then traced into their counterparts in international legal theory, in an illustration of the degree to which that theory can draw upon contrasting ideas about custom's significance. The discussion aims to highlight the assumptions the orthodox sources theory has taken for granted, and to reinvigorate the alternative position which challenge those views. To evaluate those challenges, their manifestations at international junctures are considered alongside their corresponding notions of authority, law and community. Where these appear to correspond with understandings about the present international system, the paradigms offer alternative pictures to be rebuilt into doctrines of customary law. This study argues, however, that international legal theory cannot rely upon only one of the conceptions if it is to explain and utilise custom as a legal concept. Instead, this paper suggests a reconception of custom which seeks to reconcile the contributions each paradigm makes, by formulating a notion of 'compound custom' to link the foundational social element of custom with its de facto operation and the more formal processes that generate agreement and obligation. This paradigm of 'compound custom' offers an alternative basis from which international legal theory may seek to build new theories and doctrines to explain what is truly customary about customary international law.