This collection of chapters provides the most comprehensive study of the theory and practice on the contribution of international organisations and non-State actors to the formation of customary international law. It offers new practical and theoretical perspectives on one of the most complex questions about the making of international law, namely the possibility that actors other than states contribute to the making of customary international law. Notwithstanding the completion by the International Law Commission of its work on the identification of customary international law, the making of customary international law remains riddled with acute practical and theoretical controversies which have been left unresolved and which continue to be intensively debated in both practice and scholarship. Making extensively reference to the case-law of international law courts and tribunals as well as the practice of treaty-monitoring bodies while also engaging with the most recent scholarly work on customary international law, this new volume provides innovative tools and guidance to legal scholars, researchers in law, law students, lecturers in law, practitioners, legal advisers, judges, arbitrators, and counsels as well as tools to address contemporary questions of international law-making.
malfunctioning of the dominant approach of custom as a ‘source’ ofinternationallaw, and suggests avenues to refresh international lawyers’ reflections on customary international law.
1 Opinio juris and State practice in the dominant approach to customary international law
Despite the widespread scholarly inclination to extract the two-element variant of the doctrine of customary law from Article 38 of the Statute of the Permanent Court of International Justice and the International Court of Justice, it can be defended that the two elements of custom, namely, practice
Commission plays in international law today, as it is argued below in this chapter, remains to be seen.
12 International Law Commission, A/CN.4/672 (n 3), 2/68, fn 6.
13 Sir RY Jennings , ‘ What Is International Law and How Do We Tell When We See It ’ in Martti Koskenniemi (ed), The Library of Essays in International Law: SourcesofInternationalLaw ( Ashgate 1981 ) 60 .
14 International Law Commission, A/71/10 (n 7), 81.
15 ibid 101.
16 Once the General Assembly has taken action in relation to a final draft of the Commission, such as by
practice of the community of international lawyers who construct social arrangements that orientate the way in which an emerging customary rule can be argued. That would include, among others, the use of a technical legal language that takes into account the orthodox discourse on the sourcesofinternationallaw, preferably (and ironically) including the orthodox two-element approach of practice and opinio juris ; reference to the rule being the product of State consent or acquiesce as well as arguments trying to prove its present; 90 as well as harmony between the
character seems, in the eyes of the author of this chapter, rather overblown. The first construction is the very principle that non-State actors contribute to the formation of custom. Since the inception of international law, they have been playing a crucial role in the making of norms, including customary norms. 4 Whilst such a role has never been captured by the modern categories of the doctrine of the sourcesofinternationallaw, there seems to be no reason why recognising their cardinal (albeit informal or indirect) contribution to the custom-making process ought to
principle will provide a consensual starting point for future debates. Lastly, by offering some tentative thoughts as to the relationship between subjects and sourcesofinternationallaw, the chapter suggests there are good legal grounds why the International Law Commission should leave behind a State-centric view of the sourcesofinternationallaw and recognise the autonomous lawmaking power of international organisations.
1 It is generally accepted that international organisations possess, explicitly or otherwise, the power to conclude treaties, J Klabbers
Institutions ( Springer 2010 ) 777 .
69 J Klabbers , ‘ Sources of International Organizations’ Law: Reflections on Accountability ’ in J d’Aspremont and Samantha Besson (eds), The Oxford Handbook of the SourcesofInternationalLaw ( Oxford University Press 2017 ) 987 ; and A Reinisch , ‘ Sources of International Organizations’ Law: Why Custom and General Principles are Crucial ’ in J d’Aspremont and S Besson (eds), The Oxford Handbook of the SourcesofInternationalLaw ( Oxford University Press 2017 ) 1007 .
70 Reinisch (n 69
traditional, normative analysis of law. However, the International Law Commission study has an original feature which has no precedent in either the previous work of the International Law Commission on international customary law or the academic literature: according to the Conclusions, the practice of international organizations as such may, under certain circumstances, be constitutive of custom. Such a proposition has revived the scholarly debate on the sourcesofinternationallaw in general, and the relevance of international customary law in the modern international
International Community Law Review 263 .
32 E.g. North Sea Continental Shelf case (n 29) paras 75–79; Military and Paramilitary Activities in and against Nicaragua (n 29) paras 183–85; Jurisdictional Immunities of the State (Germany v Italy, Greece Intervening) 2012 ICJ Reports 99, para 55.
33 As Kammerhofer sagely notes that ‘the range of uncertainty in international law’ is often the result of basing our arguments ‘on what other lawyers before us have said, not an any objective “proof”’. J Kammerhofer, ‘Uncertainty in the Formal SourcesofInternationalLaw
International Law’, Max Planck Encyclopedia of Public International Law (2007) para 23 http://opil.ouplaw.com/view/10.1093/law:epil/9780199231690/law-9780199231690-e1476?rskey=SUFjJt&result=1&prd=EPIL accessed 29 December 2017.
9 Hugh Thirlway , The SourcesofInternationalLaw (1st edn, Oxford University Press 2014 ) 56 , n 14.
10 Anthea Roberts and Sandesh Sivakumaran, ‘Lawmaking by Nonstate Actors: Engaging Armed Groups in the Creation of International Humanitarian Law’ (2012) 37 Yale Journal of International Law 4; Sophie Rondeau, ‘Participation of