Natural Law and Customary Law Alexander Orakhelashvili* I. Introduction The principal focus of this contribution is the process whereby the threshold of law-making is crossed through the formation of customary law. This problem has multiple dimensions. Given that the doctrinal discourse on this subject occasion- ally appeals to categories not subsumable within the consensual positivism, it is necessary to examine the normative and conceptual setting in which such catego- ries can be perceived, and this above all covers natural law. It is not intended to provide a comprehensive analysis of natural law theories, but to focus on natural law in clarifying where the dividing line between positivist and extra-positivist (in- cluding naturalist) argument lies, in a way responsive to the need of the above- mentioned mainline argument of this contribution. The clarification of the natural- ist/positivist dichotomy at the start precedes the delimitation of the field of con- sensual customary rules from that of inherent rules of general international law. At the same time, this analysis will focus only on such theoretical or practical aspects of natural and customary law which directly relate to and consider the structural characteristics of international law as the inter-State legal system. The relevance of natural and customary law in general jurisprudence and legal theory is besides the point of the present analysis. The problem of customary law has received widespread doctrinal attention. The aim of this contribution is not to provide yet another comprehensive discussion of the elements of customary law but to address the issues that have not so far re- ceived the adequate attention, are left open or are subject of disagreement, and this attempt making a further doctrinal step. In particular, this analysis focuses specifi- cally on factors responsible for the crossing of the threshold of law-making in the process of custom-generation. The principal issues are the relevance of consensual element, especially the meaning of psychological element of custom-generation, the link between customary law and natural law, and the issue of inherent rules. Of all aspects of the emergence of customary law, this contribution focuses on its psy- chological element, as the most debated issue. It is intended to focus more on the nature of the process of expression of opinio juris, rather than proving opinio juris of individual rules. The relevance of the other element of customary law – State practice – is hardly ever disputed. Despite the occasional objections,1 it is firmly * LLM cum laude (Leiden); PhD (Cantab.); Junior Research Fellow, Jesus College, Oxford. 1 There are occasional objections to the role of State practice in custom-generation. Judge D e C a s t r o , following the approach of German historical school, asserted that “practice (usages) is not the foundation of customary law, but that it is the sign by which the existence of a custom may be known. The custom is produced by the community of conviction, not by the will of men, whose acts ZaöRV 68 (2008), 69-110 http://www.zaoerv.de/ © 2008, Max-Planck-Institut für ausländisches öffentliches Recht und Völkerrecht 70 Orakhelashvili recognised that customary law develops on the basis of State practice. On the other hand, the previous contributions have not so far properly located the often con- tested concept of opinio juris in the context of interaction between positivist and naturalist arguments. This contribution is neither theoretical nor exclusively practice-oriented. It ad- dresses conceptual aspects raised by customary law and its place within the struc- ture of the international legal system. This is a priority of focus and the reference to theoretical or practical aspects is meant as auxiliary to this primary task. The va- riety of writings advance different theories that must be confronted and examined. It is particularly important to bring all the relevant approaches together and assess them in terms of the governing systemic framework of international law, which has not been done for the long period of time. The lack of doctrinal consensus on the emergence of customary law2 is observable today as it was at earlier stages. In terms of evidence, there are few pronouncements on customary law made by in- ternational tribunals. The gist of the doctrinal debate relates to the understanding of these pronouncements and this contribution cannot be an exception to this pat- tern.3 II. Natural Law 1. The Essence, Origin and Development of the Concept of Natural Law Natural law (jus naturale) has during the entire history of legal science occupied a central place in terms of understanding the nature of law in general and interna- tional law in particular. The issues of its essence, origin, scope and interaction with positive law are essential in considering whether it has its place in the international legal system and can be the legitimate object of the study of international law. The only manifest this community of ideas.” Separate Opinion, Fisheries Jurisdiction (UK/Ireland), ICJ Reports 1974, 100. 2 For the latest such attempt see A. V e r d r o s s , Entstehungsweisen und Geltungsgrund des uni- versellen völkerrechtlichen Gewohnheitsrechts, ZaöRV 29 (1969), 635. 3 This contribution does not examine the issues of custom-generation at the example of peremp- tory norms of general international law (jus cogens), which is a specific problem that relates to the small group of public order rules and thus governed by specific criteria that do not necessarily apply to the mainline process of custom-generation dealt with in the present contribution. For the custom- generation process at the example of jus cogens see A. Orakhelashvili, Peremptory Norms in In- ternational Law, Oxford 2006, Chapter 5; on the same problem see also S. K a d e l b a c h , Zwingendes Völkerrecht, Berlin 1992, in particular Chapter 5, particularly at 185-188, and id., Jus Cogens, Obliga- tions Erga Omnes and Other Rules – The Identification of Fundamental Norms, in: C. Tomuschat/J.- M. Thouvenin, The Fundamental Rules of the International Legal Order, 2006, 21-41. Nor does this contribution deal with the limitations on the custom-generation process such as those provided by the existing treaty regulation in the face of conflicting State practice. On this see the International Court’s decision on Land and Maritime Boundary between Cameroon and Nigeria, General List No. 94, Judgment of 10 October 2002. ZaöRV 68 (2008) http://www.zaoerv.de/ © 2008, Max-Planck-Institut für ausländisches öffentliches Recht und Völkerrecht Natural Law and Customary Law 71 concept of natural law refers to rules and principles deducible from nature, reason, or the idea of justice. In addition, the concept of natural law also relates to phe- nomena that are not expressly denoted as natural law, but cannot be explained by reference to positivist criteria. In line with these broach characteristics, the precise definition and parameters of conceiving natural law have been evolving and alter- ing over different periods of history. This has demonstrated the different logical possibilities of viewing natural law that is not least caused by the legal, social, reli- gious or political sentiment at the relevant time. In terms of its origin, natural law is perceived as the law that is not laid down by the human authority generally competent to create law in the relevant legal system, that is the legislature in national legal systems and State consent in international law. In terms of its essence, natural law is often perceived as the law of natural state that is the law applicable to societies that have not yet established the organised le- gal community. It may or may not survive after such organised community is established. Another way of perceiving the essence of natural law is the law appli- cable to nature, that is the law regulating the most natural elements of life of hu- man beings as well as other biological creatures. Yet another possibility is to con- ceive natural law as the law expressing the essence and idea of law, the basic values law is supposed to serve and embody, that is rules expressive of the ideal of justice, or the principles concerning the inherent nature of the relevant legal institutions. Viewed from different angles, natural law may be conceived as paramount and immutable, or as subject to changes whenever the need for this arises in the rele- vant legal community. It is on occasions conceived either as divine law derived from the will of God or secular law reflective of the nature of law or of legal com- munity. The essence of natural law calls for understanding its interaction with positive law. Depending on doctrinal orientation, natural law is perceived as law from which the validity of positive law derives, or the law which sets limits to the valid- ity and operations of positive law, or again the law which provides a fallback source applicable rules and principles should positive law have no answer as to how the relevant situation is governed. Given these different logical possibilities, natural law has been accorded differ- ent relevance in different historical contexts. In one way or another, the relevance of natural law is acknowledged not only by naturalists but also within those doc- trinal trends that do not expressly state their adherence to the natural law doctrine, and even those that on their face are generally opposed to the natural law doctrine. Among the Roman jurists, natural law was viewed as the law derived from the nature of human beings, and as law expressive of the basic ideas of justice. Accor- ding to C i c e r o , natural law is immutable. In Middle Ages, the divine concept of God-given natural law acquired increasing relevance, especially in the writings of Thomas A q u i n a s who at the same time did not view it as the immutable law.