Methods of Identification of International Custom: A New Role for Opinio Juris?

  • Hanna BourgeoisEmail author
  • Jan Wouters


Over the past few years, numerous authors have articulated alternative methods for identifying rules of customary international law in those branches of international law which reflect moral considerations and are often characterised by strong opinio juris, but inconsistent State practice or even a lack of actual State practice. They generally consider the traditional method of customary law formation and identification inappropriate since it requires both consistent State practice and, in rather subordinate order, opinio juris. In 2012, the International Law Commission (ILC) eventually decided to place the topic of formation and identification of customary international law on the agenda and appointed Sir Michael Wood Special Rapporteur for the topic (Special Rapporteur). Between 2013 and 2016, the Special Rapporteur issued four reports and sixteen draft conclusions on the identification of customary international, which were subsequently commented upon by the ILC’s drafting committee. Some have criticised the ILC for taking a very classical State-centred approach to customary international law by reinforcing the central role of States in the formation of customary international law and by applying the traditional test of both consistent practice and opinio juris. This chapter argues that the ILC has left more room than one may think at first sight for a method that may further humanitarian and ethical interests without compromising on the unity and coherence of international law. Thereto, this chapter seeks to redefine the role of opinio juris in the identification of customary international law and to reconsider its relationship with practice, while simultaneously demonstrating how such an approach falls within the boundaries set out by the ILC.


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Copyright information

© Springer Nature Switzerland AG 2018

Authors and Affiliations

  1. 1.Research Foundation – Flanders (FWO) and Leuven Centre for Global Governance StudiesLeuvenBelgium
  2. 2.Institute for International Law, KU LeuvenLeuvenBelgium

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