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Treaty Interpretation And The Incorporation Of Extraneous Legal Rules

Published online by Cambridge University Press:  17 January 2008

Duncan French
Dr, Senior Lecturer in Law, University of Sheffield, United Kingdom.


This paper considers under what circumstances, and for what reasons, an international tribunal may want to range beyond the primary text of a treaty to determine its ‘correct’ meaning; such extraneous legal material potentially including rules of customary international law, other treaties between the parties, general principles of law, and documents of a ‘soft law’ nature. The paper suggests a variety of ‘mechanisms’ by which a tribunal may undertake a broader interpretative approach, though all ultimately raise the same inevitable tension between accusations of judicial activism and counter-arguments of inflexibility and insularity. Nevertheless, many tribunals and individual judges continue to utilize such techniques, particularly noticeable in some recent environmental disputes. The paper will conclude with a note of caution; that though such interpretations are becoming an increasingly significant part of modern judicial decision-making—something that is generally to be welcomed—tribunals must concurrently take care to ensure that they remain within the accepted parameters of the adjudicative function.

Copyright © British Institute of International and Comparative Law 2006

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2 8 ILM (1969) 679.

3 Libyan Arab Jamahiriya/Chad [1994] ICJ Reports 6, 21. As regards the WTO, see United States — Standards for Reformulated and Conventional Gasoline, Report of the Appellate Body (AB-1996–1) (29 Apr 1996) (WT/DS2/AB/R) and Japan—Taxes on Alcohol Beverages Report of the Appellate Body (AB-1996–2) (4 Oct 1996) (WT/DS8, 10–11/AB/R).

4 For instance, see the work of the study group established by International Law Commission on fragmentation of international law: difficulties arising from the diversification and expansion of international law (Report on Fifty-Sixth Session (2004) Supplement No 10 (A/59/10)). See also, with specific regard to UNCLOS, A Boyle ‘Further Development of the Law of the Sea Convention: Mechanisms for Change’ (2005) 54 International and Comparative Law Quarterly 563–84.

5 This raises, in turn, important questions both over the scope of the principle of intertemporality and whether that one is looking for is the intention of the parties to the dispute or, more broadly, the parties to the treaty, where this is different? On both question, see subsequent discussion.

6 Judgment of 6 Nov 2003 <>, separate opinion of Judge Buergenthal, para 22. Emphasis added.

7 One might go further and say it is also a ‘mandatory’ aspect of treaty interpretation, on which see subsequent discussion.

8 This, however, raises another question as to what area of international law does a specific treaty fall; a matter briefly considered by judge Higgins in Oil Platforms, as discussed below.

9 Thirlway, HThe Law and Procedure of the International Court of Justice 1960–1989 Part One60 British Yearbook of International Law (1989) 135–43.Google Scholar

10 For a recent and excellent discussion of this provision, see McLachlan, CThe Principle of Systemic Integration and Art 31(3)(c) of the Vienna Convention’ (2005) 54 International and Comparative Law Quarterly (2005) 279319.CrossRefGoogle Scholar

11 cf ibid 288: ‘Despite the skepticism often expressed by academic … for express references to canons of interpretation.’

12 The difficulties with principles and rules in statu nascendi are considered below.

13 ICJ Reports (1971) 16, 31.

14 ICJ Reports (1997) 7, 67. This case is not, however, without its difficulties, on which see subsequent discussion.

15 Sands, P ‘Environmental Protection in the Twenty-first Century: Sustainable Development and International Law’ in Revesz, R et al. (eds) Environmental Law, the Economy and Sustainable Development (CUP Cambridge 2000) 405.Google Scholar

17 ICJ Reports (1971) 16, 31–2.

18 See, for instance, Kentin, E ‘Sustainable Development in International Investment Dispute Settlement: the ICSID and NAFTA Experience’ in Schrijver, N and Weiss, F (eds) International Law and Sustainable Development: Principle and Practices (Martinus Nijhoff Publishers Leiden/Boston 2004) 324: ‘Critics have pointed out that, due to their background, arbitrators may be inclined to apply investment law in isolation of other fields of law.’Google Scholar

19 cf Art 38(2) ICJ Statute.

20 Judgment of 6 Nov 2003, separate opinion of judge Buergenthal, para 22.

21 ibid para 28.

22 Aust, AModern Treaty Law and Practice (CUP Cambridge 2000) 184.Google Scholar

23 Separate opinion of judge Buergenthal, para 22.

24 Separate opinion of judge Higgins, para 49.

25 As he puts it, there are ‘jurisdictional restraints on the Court's freedom of treaty interpretation’ (separate opinion of judge Buergenthal, para 28). For a general summary of the case, see Bekker, POil Platforms (Iran v United States)’ (2004) 98 American Journal of International Law 550–8.CrossRefGoogle Scholar

26 Separate opinion of judge Buergenthal, para 24.

27 Declaration of judge Koroma.

28 Separate opinion of judge Simma, para 9.

29 Separate opinion of judge Buergenthal, para 29.

30 Judgment of 6 Nov 2003, para 41.

31 Separate opinion of judge Buergenthal, para 29.

32 8 UST 899.

33 Separate opinion of judge Higgins, para 47.

34 ibid para 46. She goes on to note that ‘[i]t is not a provision [referring to Art XX(1)(d) of the 1955 Treaty] that on the face of it envisages incorporating the entire substance of international law on a topic not mentioned in the clause—at least not without more explanation than the Court provides’ (emphasis added).

35 Orakhelashvili, ARestrictive Interpretation of Human Rights Treaties in the Recent Jurisprudence of the European Court of Human Rights’ (2003) 14 European Journal of International Law 537.CrossRefGoogle Scholar

36 Judgment of 6 Nov 2003, para 41.

37 Separate opinion of judge Simma, para 3.

38 ibid para 9.

39 Dissenting opinion of judge Al-Khasawneh, para 9.

40 Separate opinion of judge Buergenthal, para 23.

41 Orakhelashvili, AOil Platforms (Islamic Republic of Iran v United States of America), Merits Judgment of 6 Nov 2003’ (2004) 53 International and Comparative Law Quarterly 759.CrossRefGoogle Scholar

42 ibid: ‘It is one thing to say that the Court cannot adjudicate on matters not covered by a treaty conferring jurisdiction to it, and it is quite another thing to argue that the Court should adjudicate on the matters covered by a treaty in a manner leading to the result which the parties to that treaty are not allowed at all to achieve through exercise of their contractual powers.’

43 This is not to deny the importance of jus cogens, either generally, or potentially within the case, simply, that this is not the only, or necessarily the most important, aspect.

44 As regards applicable law provisions in a compromis, a recent interesting example was the arbitral agreement between Belgium and the Netherlands concerning the Iron Rhine railway, which requested the tribunal ‘to render its decision on the basis of international law, including European law if necessary, while taking into account the Parties’ obligations under Art 292 of the EC Treaty' (Arbitration regarding the Iron Rhine Railway (Belgium v The Netherlands) (The Hague 24 May 2005) <>).

45 A not dissimilar issue of interpretation qua application might arise if a tribunal were called upon to interpret the following recitals from the preamble of the 2000 Cartagena Protocol on Biosafety (39 ILM (2000) 1027): ‘Emphasizing that this Protocol shall not be interpreted as implying a change in the rights and obligations of a Party under any existing international agreements, Understanding that the above recital is not intended to subordinate this Protocol to other international agreements’.

46 See generally, Pauwelyn, JConflict of Norms in Public International Law: How WTO Law Relates to Other Rules of Public International Law (CUP Cambridge 2003).CrossRefGoogle Scholar

47 cf ‘customary rules of interpretation are, so far, the only portions of customary international law to have found their way meaningfully into WTO dispute settlement’ Matsushita, M et al. The World Trade Organization: Law, Practice and Policy (OUP Oxford 2003) 64).Google Scholar

48 It is beyond the scope of this paper to include even a representative sample of international treaties which expressly incorporate other international rules. However, one particularly interesting if slightly different example is North American Free Trade Agreement (NAFTA) (32 ILM (1993) 289 and 605) Art 104: ‘In the event of any inconsistency between this Agreement and the specific trade obligations set out in [certain environmental agreements]…such obligations shall prevail to the extent of the inconsistency, provided that where a Party has a choice among equally effective and reasonably available means of complying with such obligations, the Party chooses the alternative that is the least inconsistent with the other provisions of this Agreement…’.

49 See, for instance, Art 221 UNCLOS.

50 McLachlan (n 10) 314: ‘although the United States had not ratified UNCLOS, it had accepted during the course of argument [in Shrimp-Turtle] that the relevant provisions for the most part reflected international customary law.’

51 cf Southern Bluefin Tuna Cases (New Zealand v Japan; Australia v Japan), (Provisional Measures) (ITLOS) (1999) (39 ILM (2000) 1359), separate opinion of Judge Treves: ‘Even though… [the 1995 Straddling Stocks] Agreement is independent from the United Nations Law of the Sea Convention, it has remarkable links with it. Article 4 provided that the Agreement “shall be interpreted and applied in the context of and a manner consistent with the [Unitd Nations Law of the Sea] Convention”’ (para 10). One should note, of course, that the Straddling Stocks Agreement was negotiated to implement the relevant provisions of UNCLOS, thus arguably creating a closer nexus between these two conventions than between UNCLOS and those other rules only referenced generically in the text.

52 Island of Palmas Case (1928) 2 RIAA 829 per Judge Huber: ‘a juridical fact must be appreciated in the light of the law contemporary with it, and not of the law in force at the time when a dispute in regard to it arises or falls to be settled.’

53 ICJ Reports (1971) 16, 31.

54 Thirlway (n 9) 136–7.

55 ICJ Reports (1997) 7, 67–8.

56 Thirlway (n 9) 137.

57 ICJ Reports (1997) 7, 78.

58 ICJ Reports (1978) 3, 32. See also Case concerning Kasikili/Sedudu Island (Botswana/Namibia) [1999] ICJ Reports declaration per Judge Higgins, 1045 at 1113: ‘The term “the main channel” is not a “generic term” (cf Aegean Sea Continental Shelf case, ICJ Reports 1978, para 77)–that is to say, a known legal term, whose content the Parties expected would change through time’.

59 Thirlway (n 9) 142.

60 AB-1998-4, 12 Oct 1998 (WT/DS58/AB/R).

61 para 129.

62 para 130.

63 This raises, however, the complex issue of the relationship between GATT 1947 and GATT 1994. See Art II(4) WTO Agreement: ‘The General Agreement on Tariffs and Trade 1994 … is legally distinct from the General Agreement on Tariffs and Trade, dated 30 Oct 1947’.

64 para 131.

65 Note 114.

66 ICJ Reports (1971) 16, 31. Cf Gabčíkovo-Nagymaros ICJ Reports (1997) 122, separate opinion per Judge Bedjaoui: ‘the essential basis for the interpretation of a treaty remains the “fixed reference” to contemporary international law at the time of its conclusion. The “mobile reference” to the law which will subsequently have developed can be recommended only in exceptional cases.’

67 cf Thirlway (n 9) 137: ‘It may be objected that the ‘entire legal system prevailing’ … included the principle of intertemporal law, so that … [the sentence] … rather evades than meets the difficulty’. See also Iron Rhine Railway (2005) para 79: ‘Art 31, para 3, subpara (c) of the Vienna Convention also requires there to be taken into account “any relevant rules of international law applicable in the relations between the parties.” The intertemporal rule would seem to be one such “relevant rule”.’

68 Iron Rhine Railway (2005) para 80.

69 ibid para 82.

70 ICJ Reports (1997) 7, 68.

71 It is to be noted that in the literature, the notion or principle of contemporaneity is used both to mean what I have previously referred to as the principle of intertemporality (arguably the traditional sense) and to reflect how I most often use the term, somewhat in line with Vice President Weeramantry's view in Gabčíkovo-Nagymaros.

72 Art 31(1): ‘A treaty shall be interpreted in good faith in accordance with the ordinary meaning to be given to the terms of the treaty in their context and in the light of its object and purpose.’

73 Sands, P ‘Sustainable Development: Treaty, Custom, and the Cross-fertilization of International Law’ in Boyle, A and Freestone, D (eds) International Law and Sustainable Development—Past Achievements and Future Challenges (OUP Oxford 1999) 4950.Google Scholar

74 ILC Report (n 4) 301.

75 McLachlan (n 10) 280.

76 Aust (n 22) 183: ‘[t]he meaning of the expression … is not clear but should probably be construed strictly, so that the article would not apply when a general treaty impinges indirectly on the content of a particular provision of an earlier treaty.’

77 In addition, as McLachlan notes, in contrasting the rule of interpretation contained within article 31(3)(c) with these other approaches, ‘[i]nterpretation, on the other hand, precedes all of these techniques, since it is only by means of a process of interpretation that it is possible to determine whether there is in fact a true conflict of norms at all’ (McLachlan (n 10) 286).

78 ibid 280.

79 This specialism refers not only to the law developed, but also very often to the diplomats and lawyers involved in such legal developments.

80 ILC Report (n 4) 301.

81 ibid 300.

82 See Boyle (n 4) 569: ‘If the integrity and global character of … [UNCLOS] are to be preserved, courts must necessarily approach interpretation by reference to Art 31(3)(c) with some caution.’

83 cf Yearbook of the International Law Commission 1966, Vol II 222: ‘It [the Commission] considered that … the relevance of rules of international law for the interpretation of treaties in any given case was dependent on the intentions of the parties, and that to attempt to formulate a rule covering comprehensively the temporal element would present difficulties.’

84 ILC Report (n 4) n 650.

85 Sands (n 73) 57.

86 Judgment of 6 Nov 2003, separate opinion of Judge Higgins, para 46.

87 ibid. Emphasis added.

89 McLachlan (n 10) 313–15.

90 I have reworked McLachlan's classification, somewhat, as he sees this first exception not as a qualification but as a further acceptable understanding of Art 31(3)(c). For ease presentation, however, I consider it makes more sense to consider it as a qualification.

91 McLachlan (n 10) 315.

92 McLachlan goes further by noting that ‘Art 31 is concerned with the promulgation of a general rule, which would apply to the interpretation of a treaty irrespective of whether any particular parties to it may happen to be in dispute’ (McLachlan (n 10) 315).

93 Cf Boyle, above n 4 at 571, n 43: ‘Apart from being inconsistent with the ILC Commentary on Art 31(3), this leaves unanswered the question how the article should be applied in other contexts, eg by treaty COPs, the UN, or foreign ministries.’

94 McLachlan (n 10) 314.

95 See Al-Adsani v United Kingdom (34 EHRR 11 (2002) 289, para 55): ‘[The European Convention on Human Rights] … cannot be interpreted in a vacuum … The Convention should so far as possible be interpreted in harmony with other rules of international law of which it forms part, including those relating to the grant of State immunity.’ cf Orakhelashvili (n 35) 560: ‘it appears that the Court's approach in Al-Adsani consists not in interpretation, but merely of non-application of Art 6 to the cases where it would otherwise apply.’

96 As an example, see Marvin Roy Feldman Karpa v United Mexican States (ICSID Case No ARB(AF)/99/1) (40 ILM (2001) 615) para 30: ‘Given the legal and the factual back ground of this case, the Tribunal deems it appropriate to recall that, under general international law…’ and para 33: ‘This result, obtained under general principles of international law, has now to be checked against the NAFTA legal framework’ (emphases added).

97 Judgment of 2 July 2003 (42 ILM (2003) 1118).

98 See text related to n 70.

99 See Kasikili/Sedudu Island [1999] ICJ Reports 1045, 1060: ‘In order to illuminate the meaning of words agreed upon in 1890, there is nothing that prevents the Court from taking into account the present-day state of scientific knowledge, as reflected in the documentary material submitted to it by the Parties.’

100 This is also not to ignore the doubly contested notion that environmental principles may find legitimacy in treaty interpretation as general principles of law.

101 ICJ Reports (1997) 7, 113: ‘In the application of an environmental treaty, it is vitally important that the standards in force at the time of application would be the governing standards.’

102 ICJ Reports (1997) 7, 78.

103 R Higgins ‘Natural Resources in the Case Law of the International Court’ in Boyle and Freestone (eds) (n 73) 111: ‘an innovation not only in the jurisprudence of the Court but also in the law relating to utilization of natural resources.’

104 cf A Boyle ‘The Gabčíkovo-Nagymaros Case: New Law in Old Bottles’ (1977) 8 Yearbook of International Environmental Law 14: ‘One can only guess at the instruments that the Court had in mind … It tells us much about the nature of contemporary international lawmaking that the Court seemed happy to treat a number of these new norms as law, that the parties must take account of, without further reference to state practice or authority.’

105 V Lowe ‘Sustainable Development and Unsustainable Arguments’ in Boyle and Freestone (eds) (n 73) 20.

106 ibid.

107 Birnie, P and Boyle, AInternational Law and the Environment (2nd edn OUP Oxford 2002) 95.Google Scholar

108 Judgment of 2 July 2003, para 101.

109 ‘but only insofar as such law and practice are relevant’ (ibid).

110 The tribunal, however, raised the question whether actualization was necessary ‘of a treaty made scarcely ten years earlier’ (para 103).

111 para 102.

112 Specifically, the 1999 Aarhus Convention on Access to Information, Public Participation in Decision-Making and Access to Justice in Environmental Matters (now in force) and draft proposals for a related EC directive.

113 McDorman, TAccess to Information under Article 9 of the OSPAR convention’ (2004) 98 American Journal of International Law 337. See also Iron Rhine Railway (2005): ‘[t]here is considerable debate as to what, within the field of environmental law, constitutes “rules” or “principles”; what is “soft law”; and which environmental treaty law or principles have contributed to the development of customary international law … The mere invocation of such matters does not, of course provide the answers … ’ (para 58).CrossRefGoogle Scholar

114 ibid 338.

115 ibid.

116 cf paragraph 145: ‘this submission is confirmed by Articles 4 and 5 of the International Law Commission Draft Articles on the Responsibility of States for Internationally Wrongful Acts.’ This may, of course, be a moot point as these articles may be taken to reflect customary international law, though the tribunal does not say this expressly.

117 Quoting from Maritime Delimitation and Territorial Questions between Qatar and Bahrain [2001] ICJ Reports 40, 68. See also Art 18 of the 1969 Vienna Convention on the Law of Treaties.

118 Article 9 OSPAR (2003), dissenting opinion of Griffith, para 19.

119 Separate opinion of Judge Treves, para 10. Emphasis added. Cf Arbitral Tribunal constituted under annex VII of the United Nations convention on the Law of the Sea: Southern Bluefin Tuna Case (Australia and New Zealand v Japan) (Award on Jurisdiction and Admissibility) (2000) (39 ILM (2000) 1359) para 71: ‘Finally, the Tribunal observes that, when it comes into force, the [Straddling Stocks] Agreement…should, for States Parties to it, not only go far towards resolving procedural problems that have come before this Tribunal but, if the Convention is faithfully and effectively implemented, ameliorate the substantive problems that have divided the Parties.’ Nevertheless, the key point to note is that the arbitral tribunal was not prepared to give effect to the Straddling Stocks agreement prior to entry into force.

120 Shrimp-Turtle (1998) para 130. Moreover, in its report, the Appellate Body makes explicit reference to both official non-binding texts, such as the 1992 Rio Declaration on Environment and Development and Agenda 21, as well as more general policy documents, such as the 1987 report of the World Commission on Environment and Development, Our Common Future.

121 Boyle (n 104) 14: ‘Judge Weeramantry's expansive and eloquent use of general principles of law will doubtless add to his reputation for creative and original perspectives on the legal process.’

122 ICJ Reports (1997) 7, 113–14. See also Weeramantry's, dissenting opinion in Kasikili/Sedudu Island, ICJ Reports (1999) 1045, 1183: ‘Environmental standards transcend temporal barriers … Consequently, in environmental matters, today's standards attach themselves to yesterday's transactions, and must be given due effect in judicial determinations stemming from them.’Google Scholar

123 Mox Plant (Provisional Measures) (2001) Order of 3 Dec 2001 (41 ILM (2002)405), separate opinion of Judge Wolfrum: ‘It is still a matter of discussion whether the precautionary principle or the precautionary approach in international environmental law has become part of international customary law.’

124 AB-1997–4, 16 Jan 1998 (WT/DS26/AB/R, WT/DS48/AB/R).

125 para 124. Emphasis removed.

126 Similar language can be seen in the more recent decision of ITLOS in Case Concerning Land Reclamation by Singapore in and around the Straits of Johor (Malaysia v Singapore) (Provisional Measures) (2003) (Order of 8 Oct 2003) para 99: ‘prudence and caution require [the parties] establish mechanisms for exchanging information and assessing the risks or effects of land reclamation works and devising ways to deal with them in areas concerned.’

127 Beef Hormones (1998) para 124.

128 As a recent example of the potential role of the precautionary principle on treaty interpretation, see the dissenting opinion by Griffith in Article 9 OSPAR (2003). In particular, relying explicitly on the precautionary principle, he argued that the finding of the majority ‘that Ireland “has failed to demonstrate” adverse effect … must be vitiated as predicated upon the wrong approach to the burden of proof’ (para 75).

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