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

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Global Justice, Human Rights and the Modernization of International Law

Abstract

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.

Respectively, PhD Fellow of the Research Foundation—Flanders (FWO), Leuven Centre for Global Governance Studies—Institute for International Law, KU Leuven, and Jean Monnet Chair ad personam, Professor of International Law and International Organizations, Director, Leuven Centre for Global Governance Studies—Institute for International Law, KU Leuven.

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Notes

  1. 1.

    See Brierly and Clapham (2012), p. 57; or Fonte (2011), p. 104.

  2. 2.

    Roberts (2001), p. 764.

  3. 3.

    Ibid., p. 758.

  4. 4.

    Henkin (1995a), p. 32; as referred to by Roberts (2001), p. 764.

  5. 5.

    International Law Commission, Second report on identification of customary international law by Michael Wood, UN Doc. A/CN.4/672, 22 May 2014, p. 2.

  6. 6.

    International Law Commission, Provisional summary record of the 3132nd meeting, sixty-forth session (first part), UN Doc. A/CN.4/SR.3132, 7 June 2012, p. 16.

  7. 7.

    International Law Commission, First report on formation and evidence of customary international law by Michael Wood, UN Doc. A/CN.4/663, 17 May 2013; International Law Commission, Second report on identification of customary international law by Michael Wood, UN Doc. A/CN.4/672, 22 May 2014; International Law Commission, Third report on identification of customary international law by Michael Wood, UN Doc. A/CN.4/682, 27 March 2015; International Law Commission, Fourth report on identification of customary international law by Michael Wood, UN Doc. A/CN.4/695, 8 March 2016.

  8. 8.

    International Law Commission, Text of the draft conclusions provisionally adopted by the Drafting Committee on identification of customary international law, sixty-eight session (2 May–10 June and 4 July–12 August 2016), UN Doc. A/CN.4/L.872, 30 May 2016.

  9. 9.

    International Law Commission, Report of the International Law Commission on the work of its sixty-eighth session (2 May–10 June and 4 July–12 August 2016), UN General Assembly Official Records, sixty-eight session, Supplement No 10, Chapter V: Identification of customary international law, UN Doc. A/71/10.

  10. 10.

    See for example, Arajärvi (2017), p. 31; Deplano (2017), p. 232; or Odermatt (2017).

  11. 11.

    See 2016 Draft Conclusion 4, para. 1, International Law Commission, Text of the draft conclusions provisionally adopted by the Drafting Committee on identification of customary international law, sixty-eight session (2 May–10 June and 4 July–12 August 2016), UN Doc. A/CN.4/L.872, 30 May 2016 (“The requirement, as a constituent element of customary international law, of a general practice means that it is primarily the practice of States that contributes to the formation, or expression, of rules of customary international law.”). See also International Law Commission, Third report on identification of customary international law by Michael Wood, UN Doc. A/CN.4/682, 27 March 2015, para. 70 (“States remain the primary subjects of international law and, as explained in the second report, it is primarily their practice that contributes to the formation, and expression, of rules of customary international law.”); Nolte (2017), p. 11; Odermatt (2017), p. 493.

  12. 12.

    See Brierly and Clapham (2012), p. 57. See also an overview by Roberts (2001), pp. 757–761; or Thirlway (2015), p. 498.

  13. 13.

    Thirlway (2015), p. 498.

  14. 14.

    Henkin (1995b), pp. 180–181; Henkin (1995a), p. 38; Roberts (2001), p. 777; Simma and Alston (1992), p. 99; Thirlway (2015), p. 499.

  15. 15.

    Thirlway (2014), p. 177; Thirlway (2015), p. 499. See also Roberts (2001), p. 777; Schachter (1991), pp. 330–361; or Simma and Alston (1992), pp. 99–100.

  16. 16.

    Meron (2005), p. 821.

  17. 17.

    Frulli (2015), p. 87.

  18. 18.

    Ibid., p. 90.

  19. 19.

    Wouters and Ryngaert (2009), p. 114.

  20. 20.

    Müllerson (1998), pp. 161–162.

  21. 21.

    See for example, Jennings (1981), p. 67; Guzman (2005), p. 153; or Lepard (2010). See however for critiques of these alternative approaches, Goldsmith and Posner (2005), pp. 132–133; or Byers (1999), p. 165.

  22. 22.

    See for example, Schachter (1982), pp. 334–335; Meron (1989), pp. 92–94; Flauss (1998), p. 65; Kolb (2003), p. 129; Cohen (2012), p. 388; or Lillich (1996), pp. 12–14.

  23. 23.

    See for example, Kolb (2003), p. 129; Meron (2011), p. 32; or Cassese (2005), pp. 160–161.

  24. 24.

    See for example, Schabas (2009), p. 77.

  25. 25.

    See also the work of the International Law Association, Committee on Formation of Customary (General) International Law, Final Report, Statement of Principles Applicable to the Formation of General Customary International Law, Report of the 69th Conference, London, 2000, p. 742 and 751–752 (stating on the one hand that “a substantial manifestation of acceptance by States that a customary rule exists may compensate for a relative lack of practice” and on the other hand that “it is not always and probably not even usually, necessary to prove the existence of any sort of subjective element in addition to the objective element.”).

  26. 26.

    International Law Commission, Second report on identification of customary international law by Michael Wood, UN Doc. A/CN.4/672, 22 May 2014, para. 28; Or as eloquently noted by Huang Huikang during the ILC debate on the Third Report of the Special Rapporteur: ‘uniform standards must be applied to the identification of customary international law regardless of the field of law or the intended end-user of the draft conclusions. The application of different standards would exacerbate the fragmentation of customary international law and even call its validity into question’. International Law Commission, Sixty-seventh session (first part), Provisional summary record of the 3253rd meeting, UN Doc. A/CN.4/SR.3253, 15 July 2015. See also ICJ, Ahmadou Sadio Diallo (Republic of Guinea v. Democratic Republic of the Congo), Compensation, Judgment of 12 June 2012, ICJ Reports 2012 (Declaration of Judge Greenwood) (“International law is not a series of fragmented specialist and self-contained bodies of law, each of which functions in isolation from the others; it is a single, unified system of law and each international court can, and should, draw on the jurisprudence of other international courts and tribunals, even though it is not bound necessarily to come to the same conclusions.”); or International Law Commission, First report on formation and evidence of customary international law by Michael Wood, UN Doc. A/CN.4/663, 17 May 2013, para. 19; International Law Commission, Report of the International Law Commission on the work of its fifty-eight session (1 May–9 June and 3 July–11 August 2006), UN General Assembly Official Records, sixty-first session, Supplement No 10, UN. Doc A/61/10, para. 251.

  27. 27.

    Mettraux (2005), p. 18.

  28. 28.

    International Law Commission, First report on formation and evidence of customary international law by Michael Wood, UN Doc. A/CN.4/663, 17 May 2013, para. 70; International Law Commission, Second report on identification of customary international law by Michael Wood, UN Doc. A/CN.4/672, 22 May 2014, para. 28.

  29. 29.

    ICTY, Prosecutor v. Kupreškić et al., IT-95-16-T, Judgment of 14 January 2000, para. 527; International Law Commission, Second report on identification of customary international law by Michael Wood, UN Doc. A/CN.4/672, 22 May 2014, para. 28.

  30. 30.

    Extraordinary Chambers in the Courts of Cambodia, Supreme Court Chamber, Co-Prosecutors v. Kaing Guek Eav alias ‘Duch’ Appeal Judgment of 3 February 2012, 001/18-07-2007-ECCC/SC, para. 93; International Law Commission, Second report on identification of customary international law by Michael Wood, UN Doc. A/CN.4/672, 22 May 2014, para. 28.

  31. 31.

    Worster (2013), p. 470.

  32. 32.

    ICJ, Delimitation of the Maritime Boundary in the Gulf of Maine Area (Canada v. United States), Judgment of 20 January 1982, ICJ Reports 1984, para. 111 (italics added); Worster (2013), p. 470.

  33. 33.

    ICJ, Armed Activities on the Territory of the Congo (D.R. Congo v. Uganda), Judgment of 19 December 2005, ICJ Reports 2005, paras 161–162, 213–214, 244; ICJ, Case Concerning Military and Paramilitary Activities in and Against Nicaragua (Nicaragua v. United States), Merits, Judgment of 27 June 1986, ICJ Reports 1986, paras 215, 218; ICJ, Corfu Channel (United Kingdom of Great Britain and Northern Ireland v. Albania), Merits, Judgment of 9 April 1949, ICJ Reports 1949, p. 22; Worster (2013), p. 470.

  34. 34.

    Worster (2013), pp. 470–471.

  35. 35.

    Ibid., pp. 470–471.

  36. 36.

    (Stating that “[t]he ICJ in many cases emphasized that partly by virtue of their humanitarian character many norms articulated in treaties involving international humanitarian law now form part of customary law.”) Lepard (2010), pp. 146–147.

  37. 37.

    Ibid., p. 146; ICJ, Corfu Channel (United Kingdom of Great Britain and Northern Ireland v. Albania), Merits, Judgment of 9 April 1949, ICJ Reports 1949, p. 22.

  38. 38.

    ICJ, Case Concerning Military and Paramilitary Activities in and Against Nicaragua (Nicaragua v. United States), Merits, Judgment of 27 June 1986, ICJ Reports 1986, para. 218; ICJ, Legality of the Threat or Use of Nuclear Weapons, Advisory Opinion, Judgment of 8 July 1996, ICJ Reports 1996, paras 79, 86; Lepard (2010), pp. 146–147.

  39. 39.

    See for example, ICJ, Case Concerning Military and Paramilitary Activities in and Against Nicaragua (Nicaragua v. United States), Merits, Judgment of 27 June 1986, ICJ Reports 1986; ICTY, Appeals Chamber, Prosecutor v. Tadic, IT-94-1-A, Judgment of 15 July 1999; ICTR, Appeals Chamber, Feidinand Nahimana, Jean-Bosco Barayagwiza, and Hassan Ngeze v. The Prosecutor, ICTR-99-52-A, Judgment of 28 November 2007; ICTY, Prosecutor v. Kupreškić et al., IT-95-16-T, Judgment of 14 January 2000; or Extraordinary Chambers in the Courts of Cambodia, Supreme Court Chamber, Co-Prosecutors v. Kaing Guek Eav alias ‘Duch’ Appeal Judgment of 3 February 2012, 001/18-07-2007-ECCC/SC; See for criticism, Meron (2005), p. 819; Roberts (2001), pp. 758–759; and Simma and Alston (1992), pp. 96–97.

  40. 40.

    See also the criticism by Thirlway (2014), pp. 185–190.

  41. 41.

    ICJ, Corfu Channel (United Kingdom of Great Britain and Northern Ireland v. Albania), Merits, Judgment of 9 April 1949, ICJ Reports 1949, p. 22 (italics added) (Particularly, the ICJ noted that “[t]he obligations incumbent upon the Albanian authorities consisted in notifying, for the benefit of shipping in general, the existence of a minefield in Albanian territorial waters and in warning the approaching British warships of the imminent danger to which the minefield exposed them. Such obligations are based, not on the Hague Convention of 1907, No. VTII, which is applicable in time of war, but on certain general and well-recognized principles, namely: elementary considerations of humanity, even more exacting in peace than in war; the principle of the freedom of maritime communication; and every State’s obligation not to allow knowingly its territory to be used for acts contrary to the rights of other States.”).

  42. 42.

    Thirlway (2014), p. 186.

  43. 43.

    ICJ, Case Concerning Military and Paramilitary Activities in and Against Nicaragua (Nicaragua v. United States), Merits, Judgment of 27 June 1986, ICJ Reports 1986, paras 215, 218 (The ICJ added that it considered it justified to judge the conduct of the US according to the fundamental general principles of humanitarian law, which result inter alia from “the laws of humanity and the dictates of the public conscience”).

  44. 44.

    ICJ, Legality of the Threat or Use of Nuclear Weapons, Advisory Opinion, Judgment of 8 July 1996, ICJ Reports 1996, para. 78.

  45. 45.

    Ibid., para. 74 (italics added).

  46. 46.

    Ibid., para. 75.

  47. 47.

    Ibid., para. 78.

  48. 48.

    Ibid., para. 79.

  49. 49.

    Ibid., para. 79 (italics added).

  50. 50.

    Thirlway (2014), p. 187.

  51. 51.

    ICJ, Legality of the Threat or Use of Nuclear Weapons, Advisory Opinion, Judgment of 8 July 1996, ICJ Reports 1996, pp. 493–494 (Dissenting Opinion by Judge Weeramantry). See also Thirlway (2014), p. 187.

  52. 52.

    ICJ, Legality of the Threat or Use of Nuclear Weapons, Advisory Opinion, Judgment of 8 July 1996, ICJ Reports 1996, p. 493 (Dissenting Opinion by Judge Weeramantry).

  53. 53.

    Ibid., pp. 409–410 (Dissenting Opinion by Judge Shahabuddeen). See also Thirlway (2014), p. 187.

  54. 54.

    (Italics added).

  55. 55.

    Thirlway (2014), p. 190.

  56. 56.

    ICJ, Case Concerning United States Diplomatic and Consular Staff in Iran (United States v. Iran), Judgment of 24 May 1980, ICJ Reports 1980, para. 91 (italics added). (Particularly stating the following: “Wrongfully to deprive human beings of their freedom and to subject them to physical constraint in conditions of hardship is in itself manifestly incompatible with the principles of the Charter of the United Nations, as well as with the fundamental principles enunciated in the Universal Declaration of Human Rights.”). Schachter has contended that the ICJ only “rhetorically relied on the Declaration as a touchstone of legality”, Schachter (1991), p. 339; Wouters and Ryngaert (2009), p. 123.

  57. 57.

    Wouters and Ryngaert (2009), pp. 123–124.

  58. 58.

    ICTY, Appeals Chamber, Prosecutor v. Tadic, Decision on the Defence Motion for Interlocutory Appeal on Jurisdiction, IT-94-1, Judgment of 2 October 1995, para. 119 (italics added) (“Indeed, elementary considerations of humanity and common sense make it preposterous that the use by States of weapons prohibited in armed conflicts between themselves be allowed when States try to put down rebellion by their own nationals on their own territory.”).

  59. 59.

    As held by the ICJ in the Nicaragua case: “the Geneva Conventions are in some respects a development, and in other respects no more than the expression, of such principles [read: fundamental general principles of humanitarian law] […]. [A]n obligation [to respect and to ensure respect for the Geneva Conventions in all circumstances] does not derive only from the Conventions themselves, but from the general principles of humanitarian law to which the Conventions merely give specific expression”, ICJ, Case Concerning Military and Paramilitary Activities in and Against Nicaragua (Nicaragua v. United States), Merits, Judgment of 27 June 1986, ICJ Reports 1986, p. 218 and 220; Wouters and Ryngaert (2009), p. 124.

  60. 60.

    Wouters and Ryngaert (2009), p. 124.

  61. 61.

    Thirlway (2014), p. 189.

  62. 62.

    See also Boas (2012), p. 90.

  63. 63.

    ICJ, South West Africa Cases (Ethiopia v. South Africa; Liberia v. South Africa), Second Phase, Judgment of 18 July 1966, ICJ Reports 1966, para. 49.

  64. 64.

    For a comprehensive discussion on the various definitions of opinio juris which have been suggested in the literature on international law, see Dahlman (2012).

  65. 65.

    ICJ, North Sea Continental Shelf Cases (Federal Republic of Germany v. Denmark; Federal Republic of Germany v. Netherlands), Judgment of 20 February 1969, ICJ Reports 1969, para. 77 (italics added).

  66. 66.

    Ibid., pp. 104 and 130 (Separate Opinion of Judge Fouad Ammoun) (italics added).

  67. 67.

    ICJ, Colombian-Peruvian asylum case (Columbia v. Peru), Judgment of 20 November 1950, ICJ Reports 1950, p. 286 (italics added).

  68. 68.

    ICJ, Barcelona Traction, Light and Power Company, Limited (Belgium v. Spain), Judgment of 5 February 1970, ICJ Reports 1970, p. 306 (Separate Opinion of Judge Ammoun) (italics added).

  69. 69.

    ICJ, Case Concerning Right of Passage over Indian Territory (Portugal v. India), Merits, Judgment of 12 April 1960, ICJ Reports 1960, p. 90 (Dissenting Opinion of Judge Moreno Quitana) (italics added).

  70. 70.

    (italics added).

  71. 71.

    Roberts (2001), p. 758.

  72. 72.

    Ibid., pp. 758, 763; Simma and Alston (1992), p. 89; Kolb (2003), p. 126.

  73. 73.

    ICJ, Case Concerning Military and Paramilitary Activities in and Against Nicaragua (Nicaragua v. United States), Merits, Judgment of 27 June 1986, ICJ Reports 1986, para. 184.

  74. 74.

    2016 Draft Conclusion 2, International Law Commission, Text of the draft conclusions provisionally adopted by the Drafting Committee on identification of customary international law, sixty-eight session (2 May–10 June and 4 July–12 August 2016), UN Doc. A/CN.4/L.872, 30 May 2016 (italics added).

  75. 75.

    2016 Draft Conclusion 9, para. 1, ibid. (italics added).

  76. 76.

    Hereby quoting Müllerson (1998), p. 163; International Law Commission, Second report on identification of customary international law by Michael Wood, UN Doc. A/CN.4/672, 22 May 2014, para. 67.

  77. 77.

    Hereby citing Thirlway (1972), p. 68; International Law Commission, Third report on identification of customary international law by Michael Wood, UN Doc. A/CN.4/682, 27 March 2015, para. 16.

  78. 78.

    International Law Commission, Third report on identification of customary international law by Michael Wood, UN Doc. A/CN.4/682, 27 March 2015, para. 16.

  79. 79.

    International Law Commission, Third report on identification of customary international law by Michael Wood, UN Doc. A/CN.4/682, 27 March 2015 (footnote 28).

  80. 80.

    Hereby quoting the representative of South Africa in the Sixth Committee, ibid., para. 16. See however the disagreement by Mr. Kamto and Mr. Petric during the ILC debates on the Third Report of the Special Rapporteur, International Law Commission, Sixty-seventh session (first part), Provisional summary record of the 3252nd meeting, UN Doc. A/CN.4/SR.3252, 12 April 2016, p. 14; International Law Commission, Sixty-seventh session (first part), Provisional summary record of the 3253rd meeting, UN Doc. A/CN.4/SR.3253, 15 July 2015, p. 8.

  81. 81.

    International Law Commission, Report of the International Law Commission on the work of its sixty-eighth session (2 May–10 June and 4 July–12 August 2016), UN General Assembly Official Records, sixty-eight session, Supplement No 10, Chapter V: Identification of customary international law, UN Doc. A/71/10, p. 84.

  82. 82.

    Roberts states that “the law is (prescription) […] what the practice has been (description) or what the practice ought to be (normativity).” Roberts (2001), p. 761. Tasoulias proposes to adopt “a disjunctive conception of the content of opinio juris, one that distinguishes two broad types of cases: (1) cases where opinio juris concerns the creation or revision of customary international law; and (2) cases where opinio juris concerns the persistence across time of a norm that has already come into existence at some earlier stage”. Tasioulas (2007), p. 202. Also Lepard proposes the following novel definition of opinio juris: “the requirement that states generally believe that it is desirable now or in the near future to have an authoritative legal principle or rule prescribing, permitting, or prohibiting certain conduct”. Lepard is, however, convinced that opinio juris is sufficient to create a customary international law norm and that State practice may serve as one source of evidence of a belief that a certain rule is desirable now or in the near future. Lepard (2010), pp. 8, 97.

  83. 83.

    See also Worster (2013).

  84. 84.

    Roberts (2001), pp. 766–767 (As noted by Roberts, “the conflicting values of description and normativity and their respective risks of being an apology for power or utopian and unachievable, represent the fundamental tension in legal argument. […] Thus, international legal argument is always dynamic. […] The dynamic between description and normativity represents the “deep doctrinal schizophrenia” of law or a “disciplinary hamster wheel” from which theorists appear unable to escape.”). See also Arajärvi (2017), p. 18.

  85. 85.

    ICJ, South West Africa Cases (Ethiopia v. South Africa; Liberia v. South Africa), Second Phase, Judgment of 18 July 1966, ICJ Reports 1966, para. 91.

  86. 86.

    Kirgis (1987), p. 149.

  87. 87.

    Ibid., p. 149.

  88. 88.

    Ibid., p. 149.

  89. 89.

    International Law Commission, Second report on identification of customary international law by Michael Wood, UN Doc. A/CN.4/672, 22 May 2014, para. 28.

  90. 90.

    Ibid., para. 28.

  91. 91.

    International Law Commission, Third report on identification of customary international law by Michael Wood, UN Doc. A/CN.4/682, 27 March 2015, para. 17.

  92. 92.

    See International Law Commission, Second report on identification of customary international law by Michael Wood, UN Doc. A/CN.4/672, 22 May 2014, para. 28; International Law Commission, Sixty-seventh session (first part), Provisional summary record of the 3252nd meeting, UN Doc. A/CN.4/SR.3252, 12 April 2016.

  93. 93.

    See also Arajärvi (2017), p. 33.

  94. 94.

    See also the comment made by Mr. Šturma, International Law Commission, Sixty-sixth session (second part), Provisional summary record of the 3226th meeting, UN Doc. A/CN.4/SR.3226, 17 July 2014; International Law Commission, Third report on identification of customary international law by Michael Wood, UN Doc. A/CN.4/682, 27 March 2015, p. 7, footnote 31.

  95. 95.

    International Law Association, Committee on Formation of Customary (General) International Law, Final Report, Statement of Principles Applicable to the Formation of General Customary International Law, Report of the 69th Conference, London, 2000, p. 753.

  96. 96.

    Wouters and Ryngaert (2009), p. 130.

  97. 97.

    Schachter (1991), p. 90; as quoted by Lepard (2010), p. 127.

  98. 98.

    International Law Commission, Second report on identification of customary international law by Michael Wood, UN Doc. A/CN.4/672, 22 May 2014, para. 29; International Law Commission, Third report on identification of customary international law by Michael Wood, UN Doc. A/CN.4/682, 27 March 2015, para. 17 (“[T]he assessment of the constituent elements needs to take account of the context in which the alleged rule has arisen and is to operate.”); International Law Commission, Report of the International Law Commission on the work of its sixty-eighth session (2 May–10 June and 4 July–12 August 2016), UN General Assembly Official Records, sixty-eight session, Supplement No 10, Chapter V: Identification of customary international law, UN Doc. A/71/10, pp. 85–86. See also ICJ, North Sea Continental Shelf Cases (Federal Republic of Germany v. Denmark; Federal Republic of Germany v. Netherlands), Judgment of 20 February 1969, ICJ Reports 1969, pp. 175–178 (Dissenting Opinion by Judge Tanaka).

  99. 99.

    International Law Commission, Report of the International Law Commission on the work of its sixty-eighth session (2 May–10 June and 4 July–12 August 2016), UN General Assembly Official Records, sixty-eight session, Supplement No 10, Chapter V: Identification of customary international law, UN Doc. A/71/10, p. 85.

  100. 100.

    2016 Draft Conclusion 6, para. 3, International Law Commission, Text of the draft conclusions provisionally adopted by the Drafting Committee on identification of customary international law, sixty-eight session (2 May–10 June and 4 July–12 August 2016), UN Doc. A/CN.4/L.872, 30 May 2016.

  101. 101.

    International Law Commission, Report of the International Law Commission on the work of its sixty-eighth session (2 May–10 June and 4 July–12 August 2016), UN General Assembly Official Records, sixty-eight session, Supplement No 10, Chapter V: Identification of customary international law, UN Doc. A/71/10, p. 92.

  102. 102.

    Ibid., p. 93.

  103. 103.

    2016 Draft Conclusion 7, paras 1 and 2, International Law Commission, Text of the draft conclusions provisionally adopted by the Drafting Committee on identification of customary international law, sixty-eight session (2 May–10 June and 4 July–12 August 2016), UN Doc. A/CN.4/L.872, 30 May 2016.

  104. 104.

    2016 Draft Conclusion 8, para. 1, ibid.

  105. 105.

    International Law Commission, Report of the International Law Commission on the work of its sixty-eighth session (2 May–10 June and 4 July–12 August 2016), UN General Assembly Official Records, sixty-eight session, Supplement No 10, Chapter V: Identification of customary international law, UN Doc. A/71/10, p. 96.

  106. 106.

    Ibid., pp. 94–95.

  107. 107.

    ICJ, Case Concerning Military and Paramilitary Activities in and Against Nicaragua (Nicaragua v. United States), Merits, Judgment of 27 June 1986, ICJ Reports 1986; Wouters and Ryngaert (2009), p. 114.

  108. 108.

    ICJ, Case Concerning Military and Paramilitary Activities in and Against Nicaragua (Nicaragua v. United States), Merits, Judgment of 27 June 1986, ICJ Reports 1986; Wouters and Ryngaert (2009), p. 114.

  109. 109.

    Wouters and Ryngaert (2009), p. 114.

  110. 110.

    Ibid., p. 114.

  111. 111.

    Ibid., p. 114.

  112. 112.

    Ibid., p. 114.

  113. 113.

    ICJ, Case Concerning Military and Paramilitary Activities in and Against Nicaragua (Nicaragua v. United States), Merits, Judgment of 27 June 1986, ICJ Reports 1986, para. 186.

  114. 114.

    Ibid., para. 186. See also the International Law Association, Committee on the Formation of Rules of Customary International Law, Final Report of the Committee: Statement of Principles Applicable to the Formation of General Customary International Law, 2000, p. 753.

  115. 115.

    ICJ, Case Concerning Military and Paramilitary Activities in and Against Nicaragua (Nicaragua v. United States), Merits, Judgment of 27 June 1986, ICJ Reports 1986, para. 186. As early as 1951 the ICJ recognised that uncertainties or contradictions do not necessarily threaten the existence of a rule of customary international law. See ICJ, Fisheries case (United Kingdom v. Norway), Judgment of 18 December 1951, ICJ Reports 1951, p. 138 (“The Court considers that too much importance need not be attached to the few uncertainties or contradictions, real or apparent, which the United Kingdom Government claims to have discovered in Norwegian practice. They may be easily understood in the light of the variety of the facts and conditions prevailing in the long period which has elapsed since 1812, and which are not such as to modify the conclusions reached by the Court [relating to the existence of a rule of customary international law].”). See also International Law Commission, Second report on identification of customary international law by Michael Wood, UN Doc. A/CN.4/672, 22 May 2014, para. 57; Meron (2005), p. 820; Thirlway (2014), p. 68; Simma and Alston (1992), p. 97; and Roberts (2001), p. 765.

  116. 116.

    ICJ, Case Concerning Military and Paramilitary Activities in and Against Nicaragua (Nicaragua v. United States), Merits, Judgment of 27 June 1986, ICJ Reports 1986, para. 188. Kirgis argues that the ICJ’s “primary reliance on normative words rather than on a combination of words and consistent deeds” in Nicaragua may be explained by “the need for stability.” See Kirgis (1987); Wouters and Ryngaert (2009), p. 114. On the role of verbal State practice, see infra, Sect. 3.2.3.

  117. 117.

    Schachter (1996), p. 538; Schachter supports the Nicaragua approach though, Schachter (1991), p. 340; Wouters and Ryngaert (2009), p. 113.

  118. 118.

    Simma and Alston (1992), p. 97.

  119. 119.

    Ibid., p. 97; See however, Cheng (1965), p. 37 (Stating that “there is no reason why an opinio juris communis may not grow up in a very short period of time among all or simply some Members of the United Nations with the result that a new rule of international customary law comes into being among them. And there is also no reason why they may not use an Assembly resolution to ‘positivize’ their new common opinio juris.”). See also Bernhardt (1987), p. 266 (Stating that he “would even accept that in exceptional circumstances no practice is necessary if a certain rule according to which a certain behaviour is either necessary or prohibited has been universally approved. In so far [he] would accept the possibility of “instant law”.”).

  120. 120.

    See also the following statement by the ICRC it its 2005 study on customary international law (as further discussed below), “Opinio juris plays an important role […] in certain situations where the practice is ambiguous, in order to decide whether or not that practice counts towards the formation of custom”.] Henckaerts and Doswald-Beck (2005), p. xlvi.

  121. 121.

    In a number of cases, the ICJ has taken into consideration verbal acts such as official statements as State practice, including in: ICJ, Fisheries Jurisdiction Case (Federal Republic of Germany v. Iceland), Merits, Judgment of 25 July 1974, ICJ Reports 1974; ICJ, Case Concerning Military and Paramilitary Activities in and Against Nicaragua (Nicaragua v. United States), Merits, Judgment of 27 June 1986, ICJ Reports 1986, para. 190; ICJ, Case Concerning the Gabčíkovo-Nagymaros Project (Hungary v. Slovakia), Judgment of 25 September 1997, ICJ Reports 1997, paras 49–58. See also support by Akehurst (1974); International Law Association, Committee on Formation of Customary (General) International Law, Final Report, Statement of Principles Applicable to the Formation of General Customary International Law, Report of the 69th Conference, London, 2000, pp. 14–15; and Villiger (1997), pp. 20–21. Certain authors do not consider verbal practice a valid indicator for the formation of a new customary international law rule. For example, d’Amato and Roberts make a clear distinction between action (State practice) and statements (opinio juris), see D’Amato (1969), pp. 89–90; d’Aspremont (2014) Customary International Law as a Dance Floor—Part II, EJIL TALK! https://www.ejiltalk.org/customary-international-law-as-a-dance-floor-part-ii/. Accessed 18 January 2018; d’Aspremont (2015); Roberts (2001), p. 757. Roberts defends this position by arguing that when using statements as evidence of State practice, this fuses “lex lata and lex ferenda”. However, in her analysis of State practice, she takes into consideration “reasons for a lack of protest over breaches” (see also infra, Sect. 3.2.4). Id. One may question, however, why protests over breaches, which are usually recorded in statements by States, can be used in the analysis of State practice, while statements as such may only serve as opinio juris. As already mentioned by Wouters and Ryngaert (2009), p. 115, “Protests could certainly be deprived of any normative aspirations (opinio juris), and thus qualify as State practice.”

  122. 122.

    Wouters and Ryngaert (2009), p. 115.

  123. 123.

    ICTY, Appeals Chamber, Prosecutor v. Tadic, Decision on the Defence Motion for Interlocutory Appeal on Jurisdiction, IT-94-1, Judgment of 2 October 1995, para. 99.

  124. 124.

    Ibid., para. 99.

  125. 125.

    Wouters and Ryngaert (2009), p. 116.

  126. 126.

    Ibid., p. 116.

  127. 127.

    Henckaerts and Doswald-Beck (2005) and Wouters and Ryngaert (2009), p. 116.

  128. 128.

    Henckaerts and Doswald-Beck (2005), p. xliv.

  129. 129.

    In its 2005 Study, the ICRC took into account verbal acts such as military manuals, national legislation, national case-law, instructions to armed and security forces, military communiqués during war, diplomatic protests, opinions of official legal advisers, comments by governments on draft treaties, executive decisions and regulations, pleadings before international tribunals, statements in international organisations and at international conferences and government positions taken with respect to resolutions of international organisations. The ICRC also considered physical acts such as, for example, battlefield behavior, the use of certain weapons and the treatment provided to different categories of persons. See ibid., p. xxxviii.

  130. 130.

    Ibid., pp. 604–607. Universal jurisdiction is generally defined as jurisdiction that finds its sole basis in the nature of a crime “without regard to where the crime was committed, the nationality of the alleged or convicted perpetrator, the nationality of the victim, or any other connection to the State exercising such jurisdiction.” See Principle 1(1) of the Princeton Principles on Universal Jurisdiction (2001), reprinted in Macedo (2004).

  131. 131.

    Henckaerts and Doswald-Beck (2005), p. 605 (“Several States have incorporated the list of war crimes contained in the Statute [of the ICJ] in their national legislation and vested jurisdiction in their courts to prosecute persons suspected of having committed such war crimes on the basis of the principle of universal jurisdiction.”).

  132. 132.

    Ibid., pp. 604–607 (The ICRC also took into account treaties such as the Geneva Conventions of 1949, the Additional Protocol I of 1977, and a number of other treaties which oblige State Parties to provide for universal jurisdiction over certain crimes, including the UN Convention against Torture and the Inter-American Convention on Forced Disappearances (See infra Sect. 3.4)).

  133. 133.

    On 3 November 2006, John B. Bellinger, the Legal Adviser of the US Department of State, and William J. Haynes, General Counsel of the US Department of Defense, sent a letter to Jakob Kellenberger, the President of the ICRC. This letter was made public in March 2007 and reproduced at: Mandsager (2007); For a response see Henckaerts (2007). See also for an early critical technical assessment by a US Department of Defence official writing in his own name: Parks (2005), pp. 208–212.

  134. 134.

    Mandsager (2007), pp. 515–516 (particularly, the letter notes: “Rather than indicating a position expressed out of a sense of a customary legal obligation, in the sense pertinent to customary international law, a State’s military manual often [properly] will recite requirements applicable to that State under treaties to which it is a party. Reliance on provisions of military manuals designed to implement treaty rules provides only weak evidence that those treaty rules apply as a matter of customary international law in non-treaty contexts. Moreover, States often include guidance in their military manuals for policy, rather than legal, reasons. For example, the United States long has stated that it will apply the rules in its manuals whether the conflict is characterized as international or non-international, but this clearly is not intended to indicate that it is bound to do so as a matter of law in non-international conflicts. Finally, the Study often fails to distinguish between military publications prepared informally solely for training or similar purposes and those prepared and approved as official government statements.”).

  135. 135.

    International Law Commission, Second report on identification of customary international law by Michael Wood, UN Doc. A/CN.4/672, 22 May 2014, para. 37.

  136. 136.

    Hereby quoting Shaw (2014), p. 54.

  137. 137.

    Hereby quoting Thirlway (1972), p. 68; International Law Commission, Third report on identification of customary international law by Michael Wood, UN Doc. A/CN.4/682, 27 March 2015, para. 16.

  138. 138.

    Wood (2016), p. 8.

  139. 139.

    2016 Draft Conclusion 6, para. 1, International Law Commission, Text of the draft conclusions provisionally adopted by the Drafting Committee on identification of customary international law, sixty-eight session (2 May–10 June and 4 July–12 August 2016), UN Doc. A/CN.4/L.872, 30 May 2016.

  140. 140.

    Note that according to 2016 Draft Conclusion 13, para. 2, “[r]egard may be had, as appropriate, to decisions of national courts concerning the existence and content of rules of customary international law, as a subsidiary means for the determination of such rules.” Ibid.

  141. 141.

    International Law Commission, Second report on identification of customary international law by Michael Wood, UN Doc. A/CN.4/672, 22 May 2014, para. 41; International Law Commission, Report of the International Law Commission on the work of its sixty-eighth session (2 May–10 June and 4 July–12 August 2016), UN General Assembly Official Records, sixty-eight session, Supplement No 10, Chapter V: Identification of customary international law, UN Doc. A/71/10, p. 92.

  142. 142.

    International Law Commission, Report of the International Law Commission on the work of its sixty-eighth session (2 May–10 June and 4 July–12 August 2016), UN General Assembly Official Records, sixty-eight session, Supplement No 10, Chapter V: Identification of customary international law, UN Doc. A/71/10, p. 91.

  143. 143.

    See Rule 151 Henckaerts and Doswald-Beck (2005), pp. 552–555 (the 2005 Study also referred to numerous treaties, including international humanitarian law treaties and statutes of international the International Criminal Tribunal for Rwanda [ICTR] and the Special Court for Sierra Leone, as well as to practice of international organisations and case law of international criminal tribunals including the ICTR and the ICTY (see infra, Sects. 3.3 and 3.4)); Wouters and Ryngaert (2009), p. 115.

  144. 144.

    Simma and Paulus (1999) (Stating that “opinio juris may be deduced from the conclusion of treaties or voting records in international fora, up to the point where practice and opinio juris cannot be clearly distinguished from each other.”); Wouters and Ryngaert (2009), p. 115.

  145. 145.

    Wouters and Ryngaert (2009), p. 115.

  146. 146.

    International Law Commission, Second report on identification of customary international law by Michael Wood, UN Doc. A/CN.4/672, 22 May 2014, para. 80.

  147. 147.

    Ibid., para. 70.

  148. 148.

    Ibid., para. 74.

  149. 149.

    International Law Commission, Third report on identification of customary international law by Michael Wood, UN Doc. A/CN.4/682, 27 March 2015, para. 15.

  150. 150.

    Ibid., para. 15. See also Thirlway (2015), p. 502.

  151. 151.

    2016 Draft Conclusion 3, para. 2, reads as follows: “Each of the two constituent elements is to be separately ascertained. This requires an assessment of evidence for each element”, International Law Commission, Text of the draft conclusions provisionally adopted by the Drafting Committee on identification of customary international law, sixty-eight session (2 May–10 June and 4 July–12 August 2016), UN Doc. A/CN.4/L.872, 30 May 2016.

  152. 152.

    International Law Commission, Report of the International Law Commission on the work of its sixty-eighth session (2 May–10 June and 4 July–12 August 2016), UN General Assembly Official Records, sixty-eight session, Supplement No 10, Chapter V: Identification of customary international law, UN Doc. A/71/10, p. 87.

  153. 153.

    Ibid., p. 99.

  154. 154.

    Arajärvi (2017), p. 35.

  155. 155.

    Henkin (1995a), p. 36; Roberts (2001), p. 777.

  156. 156.

    Henkin (1995a), p. 38; Henkin (1995b), pp. 180–181; Roberts (2001), p. 777; Simma and Alston (1992), p. 99; Thirlway (2015), p. 499.

  157. 157.

    International Law Commission, Report of the International Law Commission on the work of its sixty-eighth session (2 May–10 June and 4 July–12 August 2016), UN General Assembly Official Records, sixty-eight session, Supplement No 10, Chapter V: Identification of customary international law, UN Doc. A/71/10, p. 90.

  158. 158.

    See 2016 Draft Conclusion 6, para. 2, International Law Commission, Text of the draft conclusions provisionally adopted by the Drafting Committee on identification of customary international law, sixty-eight session (2 May–10 June and 4 July–12 August 2016), UN Doc. A/CN.4/L.872, 30 May 2016.

  159. 159.

    2016 Draft Conclusion 6, para. 1, ibid.

  160. 160.

    International Law Commission, Report of the International Law Commission on the work of its sixty-eighth session (2 May–10 June and 4 July–12 August 2016), UN General Assembly Official Records, sixty-eight session, Supplement No 10, Chapter V: Identification of customary international law, UN Doc. A/71/10, p. 91. See also PCIJ, Lotus, Judgment of 7 September 1927, Series A No. 10, para. 76 (“Even if the rarity of the judicial decisions to be found among the reported cases were sufficient to prove in point of fact the circumstance alleged by the Agent for the French Government, it would merely show that States had often, in practice, abstained from instituting criminal proceedings, and not that they recognized themselves as being obliged to do so; for only if such abstention were based on their being conscious of having a duty to abstain would it be possible to speak of an international custom.”); ICJ, Arrest Warrant of 11 April 2000 (Democratic Republic of the Congo v. Belgium), Judgment of 14 February 2002, ICJ Reports 2002, p. 145 (Dissenting Opinion by Judge Van Den Wyngaert).

  161. 161.

    International Law Commission, Report of the International Law Commission on the work of its sixty-eighth session (2 May–10 June and 4 July–12 August 2016), UN General Assembly Official Records, sixty-eight session, Supplement No 10, Chapter V: Identification of customary international law, UN Doc. A/71/10, p. 86.

  162. 162.

    Ibid., p. 91.

  163. 163.

    Ibid., p. 91.

  164. 164.

    Roberts (2001), p. 777.

  165. 165.

    Ibid., p. 778; Henkin (1995a), p. 41.

  166. 166.

    Roberts (2001), p. 778.

  167. 167.

    ICJ, Arrest Warrant of 11 April 2000 (Democratic Republic of the Congo v. Belgium), Judgment of 14 February 2002, ICJ Reports 2002, p. 145 (Dissenting Opinion by Judge Van Den Wyngaert arguing that “[a] “negative practice” of States, consisting in their abstaining from instituting criminal proceedings, cannot, in itself, be seen as evidence of an opinio juris. Abstinence may be explained by many other reasons, including courtesy, political considerations, practical concerns and lack of extraterritorial criminal jurisdiction.”).

  168. 168.

    See also Mathias (2016), pp. 24–30.

  169. 169.

    2016 Draft Conclusion 4, para. 2, International Law Commission, Text of the draft conclusions provisionally adopted by the Drafting Committee on identification of customary international law, sixty-eight session (2 May–10 June and 4 July–12 August 2016), UN Doc. A/CN.4/L.872, 30 May 2016.

  170. 170.

    Odermatt (2017), p. 502.

  171. 171.

    International Law Commission, Report of the International Law Commission on the work of its sixty-eighth session (2 May–10 June and 4 July–12 August 2016), UN General Assembly Official Records, sixty-eight session, Supplement No 10, Chapter V: Identification of customary international law, UN Doc. A/71/10, p. 88.

  172. 172.

    Ibid., p. 89.

  173. 173.

    Ibid., p. 89. See further, Odermatt (2017) and Wessel (2016).

  174. 174.

    Blokker (2017), p. 8.

  175. 175.

    International Law Commission, Report of the International Law Commission on the work of its sixty-eighth session (2 May–10 June and 4 July–12 August 2016), UN General Assembly Official Records, sixty-eight session, Supplement No 10, Chapter V: Identification of customary international law, UN Doc. A/71/10, p. 89.

  176. 176.

    Ibid., p. 89.

  177. 177.

    Blokker (2017), pp. 8–9.

  178. 178.

    Ibid., p. 9.

  179. 179.

    Ibid., p. 9.

  180. 180.

    Not all States support this initiative, see for example the position of the Informal Expert Group on Customary International Law of the Asian-African Consultative Organization, Yee (2015).

  181. 181.

    Blokker (2017), pp. 4–6.

  182. 182.

    International Law Commission, Fourth report on identification of customary international law by Michael Wood, UN Doc. A/CN.4/695, 8 March 2016, para. 19.

  183. 183.

    2016 Draft Conclusions 6, paras 1 and 3 concerns general rules on forms of practice, whereas 2016 Draft Conclusion 8, para. 1 notes that “practice must be general”. See International Law Commission, Text of the draft conclusions provisionally adopted by the Drafting Committee on identification of customary international law, sixty-eight session (2 May–10 June and 4 July–12 August 2016), UN Doc. A/CN.4/L.872, 30 May 2016. Moreover, in the Commentaries to 2016 Draft Conclusion 8, paragraph 1, no reference is made to other actors than States, see International Law Commission, Report of the International Law Commission on the work of its sixty-eighth session (2 May–10 June and 4 July–12 August 2016), UN General Assembly Official Records, sixty-eight session, Supplement No 10, Chapter V: Identification of customary international law, UN Doc. A/71/10, pp. 94–95.

  184. 184.

    2016 Draft Conclusion 5, 2016 Draft Conclusion 6, para. 2, and 2016 Draft Conclusion 7, International Law Commission, Text of the draft conclusions provisionally adopted by the Drafting Committee on identification of customary international law, sixty-eight session (2 May–10 June and 4 July–12 August 2016), UN Doc. A/CN.4/L.872, 30 May 2016.

  185. 185.

    International Law Commission, Report of the International Law Commission on the work of its sixty-eighth session (2 May–10 June and 4 July–12 August 2016), UN General Assembly Official Records, sixty-eight session, Supplement No 10, Chapter V: Identification of customary international law, UN Doc. A/71/10, p. 91.

  186. 186.

    Blokker (2017), pp. 5–6.

  187. 187.

    2016 Draft Conclusion 10, para.1, provides that “[e]vidence of acceptance as law (opinio juris) may take a wide range of forms.”]. See International Law Commission, Text of the draft conclusions provisionally adopted by the Drafting Committee on identification of customary international law, sixty-eight session (2 May–10 June and 4 July–12 August 2016), UN Doc. A/CN.4/L.872, 30 May 2016.

  188. 188.

    International Law Commission, Report of the International Law Commission on the work of its sixty-eighth session (2 May–10 June and 4 July–12 August 2016), UN General Assembly Official Records, sixty-eight session, Supplement No 10, Chapter V: Identification of customary international law, UN Doc. A/71/10, pp. 97–101.

  189. 189.

    Blokker (2017), p. 10.

  190. 190.

    Ibid., pp. 10–11.

  191. 191.

    2016 Draft Conclusion 6, para. 2, International Law Commission, Text of the draft conclusions provisionally adopted by the Drafting Committee on identification of customary international law, sixty-eight session (2 May–10 June and 4 July–12 August 2016), UN Doc. A/CN.4/L.872, 30 May 2016 (“Forms of State practice include, but are not limited to: diplomatic acts and correspondence; conduct in connection with resolutions adopted by an international organization or at an intergovernmental conference; conduct in connection with treaties; executive conduct, including operational conduct “on the ground”; legislative and administrative acts; and decisions of national courts.”).

  192. 192.

    2016 Draft Conclusion 6, para. 1, ibid.

  193. 193.

    2016 Draft Conclusion 15, ibid.

  194. 194.

    See commentaries by Murphy (2015), pp. 830–831.

  195. 195.

    ILC Draft Conclusion 4, para. 3 reads as follows: “Conduct of other actors is not practice that contributes to the formation, or expression, of rules of customary international law, but may be relevant when assessing the practice referred to in paragraphs 1 and 2”, see International Law Commission, Text of the draft conclusions provisionally adopted by the Drafting Committee on identification of customary international law, sixty-eight session (2 May–10 June and 4 July–12 August 2016), UN Doc. A/CN.4/L.872, 30 May 2016. In a response to the concern of certain States that “the wording of draft conclusion 4, paragraph 3, dealing with the conduct of actors other than States and international organizations, was too strict, in that it does not adequately recognize the important contribution that such actors may make to international practice related to their work and the possible development of customary international law”, the Special Rapporteur stressed in his Fourth Report that “the words may be relevant when assessing the practice [of States and international organisations]”, found in paragraph 3, which acknowledge that although the conduct of “other actors” is not directly creative, or expressive, of customary international law, it may very well have an important (albeit indirect) role in the development and identification of customary international law, See International Law Commission, Fourth report on identification of customary international law by Michael Wood, UN Doc. A/CN.4/695, 8 March 2016.

  196. 196.

    International Law Commission, Report of the International Law Commission on the work of its sixty-eighth session (2 May–10 June and 4 July–12 August 2016), UN General Assembly Official Records, sixty-eight session, Supplement No 10, Chapter V: Identification of customary international law, UN Doc. A/71/10, p. 89.

  197. 197.

    Ibid., p. 89.

  198. 198.

    Ibid., p. 90.

  199. 199.

    Ibid., p. 90.

  200. 200.

    Ibid., p. 90.

  201. 201.

    ICTY, Appeals Chamber, Prosecutor v. Tadic, Decision on the Defence Motion for Interlocutory Appeal on Jurisdiction, IT-94-1, Judgment of 2 October 1995, para. 109.

  202. 202.

    ICJ, Arrest Warrant of 11 April 2000 (Democratic Republic of the Congo v. Belgium), Judgment of 14 February 2002, ICJ Reports 2002, pp. 154–155 (Dissenting Opinion by Judge Van Den Wyngaert) (italics added).

  203. 203.

    2016 Draft Conclusion 6, para. 2, International Law Commission, Text of the draft conclusions provisionally adopted by the Drafting Committee on identification of customary international law, sixty-eight session (2 May–10 June and 4 July–12 August 2016), UN Doc. A/CN.4/L.872, 30 May 2016. See also Mathias (2016) (Listing a number of acts which may play an important role in the formation of customary international law: “official meetings and correspondence between governmental representatives and organization officials, including the Secretary-General or his special envoys and representatives; the conclusion of agreements or arrangements between States and international organizations (including, but not limited to, host country agreements); the treatment of the organization, its property and its staff; the instructions provided by governments to their representatives as to which agendas should be pursued in the work of the organization, etc.”).

  204. 204.

    2016 Draft Conclusion 10, para. 2, International Law Commission, Text of the draft conclusions provisionally adopted by the Drafting Committee on identification of customary international law, sixty-eight session (2 May–10 June and 4 July–12 August 2016), UN Doc. A/CN.4/L.872, 30 May 2016.

  205. 205.

    International Law Commission, Report of the International Law Commission on the work of its sixty-eighth session (2 May–10 June and 4 July–12 August 2016), UN General Assembly Official Records, sixty-eight session, Supplement No 10, Chapter V: Identification of customary international law, UN Doc. A/71/10, p. 103.

  206. 206.

    ILC Draft Conclusion 11, para. 1, International Law Commission, Text of the draft conclusions provisionally adopted by the Drafting Committee on identification of customary international law, sixty-eight session (2 May–10 June and 4 July–12 August 2016), UN Doc. A/CN.4/L.872, 30 May 2016.

  207. 207.

    ICJ, North Sea Continental Shelf Cases (Federal Republic of Germany v. Denmark; Federal Republic of Germany v. Netherlands), Judgment of 20 February 1969, ICJ Reports 1969, para. 72; International Law Commission, Third report on identification of customary international law by Michael Wood, UN Doc. A/CN.4/682, 27 March 2015, para. 39.

  208. 208.

    ICJ, North Sea Continental Shelf Cases (Federal Republic of Germany v. Denmark; Federal Republic of Germany v. Netherlands), Judgment of 20 February 1969, ICJ Reports 1969, para. 74.

  209. 209.

    ECtHR, Van Anraat v. The Netherlands, Decision on Admissibility, 65389/09, Judgment of 6 July 2010, paras 35–36, 88 (after first having referred to the North Sea Continental Shelf and Nicaragua cases, the ECtHR held that: “it is possible for a treaty provision to become customary international [humanitarian] law. For this it is necessary that the provision concerned should, at all event potentially, be of a fundamentally norm-creating character such as could be regarded as forming the basis of a general rule of law; that there be corresponding settled State practice; and that there be evidence of a belief that this practice is rendered obligatory by the existence of a rule of law requiring it (opinio juris sive necessitates).”).

  210. 210.

    ILC Draft Conclusion 12, paras 1 and 2, International Law Commission, Text of the draft conclusions provisionally adopted by the Drafting Committee on identification of customary international law, sixty-eight session (2 May–10 June and 4 July–12 August 2016), UN Doc. A/CN.4/L.872, 30 May 2016.

  211. 211.

    ILC Draft Conclusion 12, para. 3, ibid.

  212. 212.

    International Law Commission, Sixty-seventh session (first part), Provisional summary record of the 3250st meeting, UN Doc. A/CN.4/SR.3250, 8 March 2016, pp. 10–11. See also the comments made by Mr. Hmoud during the ILC debates on the Fourth Report of the Special Rapporteur, International Law Commission, Sixty-seventh session (first part), Provisional summary record of the 3251st meeting, UN Doc. A/CN.4/SR.3251, 9 June 2015, pp. 10–11.

  213. 213.

    Deplano (2017), p. 243.

  214. 214.

    Blokker (2017), p. 9; Deplano (2017), p. 253.

  215. 215.

    ILC Draft Conclusion 13, para. 1, International Law Commission, Text of the draft conclusions provisionally adopted by the Drafting Committee on identification of customary international law, sixty-eight session (2 May–10 June and 4 July–12 August 2016), UN Doc. A/CN.4/L.872, 30 May 2016.

  216. 216.

    Henckaerts and Doswald-Beck (2005), p. xl.

  217. 217.

    See also Akehurst (1974), pp. 14–15 (“A statement that something is morally obligatory may help to create rules of international morality; it cannot help to create rules of international law.”); Reisman (1981) (“[D]emands rich in authority signals but without adequate control intention communications may yield, at least for some, expressions of morality,” but it would be “improper to call them law.”).

  218. 218.

    For a more extensive discussion on the role of ethics in the development of customary international law, see Thirlway (2014), pp. 83–86. See also Lepard (2010) (yet, as noted above, Lepard is convinced that opinio juris is sufficient to create a customary international law norm and that State practice may serve as one source of evidence of a belief that a certain rule is desirable now or in the near future.). For a more general discussion on the role of ethics in international law, see Childress (2012).

  219. 219.

    ICJ, South West Africa Cases (Ethiopia v. South Africa; Liberia v. South Africa), Second Phase, Judgment of 18 July 1966, ICJ Reports 1966, para. 49.

  220. 220.

    Ibid., para. 49.

  221. 221.

    Ibid., para. 50.

  222. 222.

    ICTY, Prosecutor v. Kupreškić et al., IT-95-16-T, Judgment of 14 January 2000, para. 524.

  223. 223.

    Schachter (1991), p. 90; as quoted by Lepard (2010), p. 127.

  224. 224.

    See criticism by Simma and Alston on Schachter’s list based on the Restatement (Third) Foreign Relations Law of the United States (1987), § 702, Simma and Alston (1992), p. 95; Schachter (1982), pp. 333–342.

  225. 225.

    Roberts (2001), p. 789 (italics added).

  226. 226.

    Ibid., p. 761; Tasioulas (2007), p. 202.

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Authors and Affiliations

  1. Research Foundation – Flanders (FWO) and Leuven Centre for Global Governance Studies, Leuven, Belgium

    Hanna Bourgeois & Jan Wouters

  2. Institute for International Law, KU Leuven, Leuven, Belgium

    Hanna Bourgeois & Jan Wouters

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  1. Hanna Bourgeois
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  1. Department of Political and International Sciences, University of Siena, Siena, Italy

    Riccardo Pisillo Mazzeschi

  2. Faculty of Law, Catholic University of Milan, Milan, Italy

    Pasquale De Sena

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Bourgeois, H., Wouters, J. (2018). Methods of Identification of International Custom: A New Role for Opinio Juris?. In: Pisillo Mazzeschi, R., De Sena, P. (eds) Global Justice, Human Rights and the Modernization of International Law. Springer, Cham. https://doi.org/10.1007/978-3-319-90227-2_5

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