Skip to main content Accessibility help

Manifest Intent and the Generation by Treaty of Customary Rules of International Law

  • Anthony D’Amato (a1)


The World Court’s recent decision in the North Sea Continental Shelf Cases is a major contribution to that branch of the theory of customary international law dealing with norm-creation by means of a treaty. The Court articulated a new methodology for determining which provisions in treaties can form the basis of universally binding customary law. As the spreading network of international conventions becomes more fine-meshed, the substantive rules of international customary law may be expected to conform more and more closely to the provisions in these conventions. The World Court has implicitly recognized this process in many prior opinions, but it was not until the Continental Shelf decision that the link between treaty and custom was focused upon with precision. I shall argue in this essay that the Court used a method which might be called the rule of manifest intent, that this method differs from a more traditional approach found in the writings of publicists, and that this new method accords well with the growing need to objectify and place upon a scientific basis the methodology by which one may determine what in fact are the rules of customary law.



Hide All

1 [1969] I.C.J. Rep. 3; 63 A.J.I.L. 591 (1969); 8 Int. Legal Materials 340 (1969).

2 The equidistance line leaves to a coastal state “all those portions of the Continental Shelf that are nearer to a point on its own coast than they are to any point on the coast of” the adjacent coastal state. [1969] I.C.J. Rep. 3, at 18.

3 Text in 52 A.J.I.L. 858 (1958).

4 [1969] I.C.J. Rep. 3, at 26.

5 Ibid, at 18.

6 Ibid.

7 Ibid, at 24.

8 Ibid, at 24-25.

9 Ibid, at 28.

10 Ibid, at 36.

11 Fuller, , The Problems of Jurisprudence 9 (temp, ed., 1949).

12 Although tangential to the present essay, it may be noted that the Court grounded the necessity for an equitable result in the customary international law of the continental shelf, particularly in the notion of “equitable principles” in the Truman Proclamation of 1945, one of the earliest components of the international law on this subject. [1969] I.C.J. Rep. 3, at 33.

13 I have attempted to spell this out in detail elsewhere. See D’Amato, ‘Treaties as a Source of General Rules of International Law,” 3 Harvard Int. Law J. 1 (1962). Cf. idem, “Legal Aspects of the French Nuclear Tests,” 61 A.J.I.L. 66, 76-77 (1967).

14 A fourth possibility considered by the Court, but irrelevant to the present essay, is whether an equidistance rule exists solely in customary or natural law. The Court decided this question in the negative.

15 “[T]his contention . . . clearly involves treating [Article 6] as a norm-creating provision which has constituted the foundation of, or has generated a rule which, while only conventional or contractual in its origin, has since passed into the general corpus of international law . . . .” [1969] LC.J. Rep. 3, at 42.

16 Ibid, at 43.

17 Ibid, at 42.

18 Ibid, at 40, 43.

19 See D’Amato, , “The Concept of Special Custom in International Law,” 63 A.J.I.L. 211 (1969).

20 [1969] LC.J. Rep. 3, at 43.

21 Ibid.

22 Article 6, par. 2, Convention on the Continental Shelf, 52 A.J.I.L. 858, 860 (1958).

28 See Schwarzenberger, , “International Jus Cogens?”, 43 Texas Law Rev. 455 (1965); Riesenfeld, , “Jus Dispositivum and Jus Cogens in International Law: In the Light of a Recent Decision of the German Supreme Constitutional Court,” 60 A.J.I.L. 511 (1966); Verdross, , “Jus Dispositivum and Jus Cogens in International Law,” 60 A.J.I.L. 55 (1966).

24 [1969] LC.J. Rep. 3, at 43.

25 Ibid.

26 Ibid.

27 Ibid, at 41.

28 Ibid, at 131.

29 Ibid, at 199.

30 52 A.J.I.L. 834 (1958).

31 Ibid, at 842.

32 Ibid, at 851.

33 [1969] I.C.J. Rep. 3, at 43.

34 Ibid.

35 Ibid, at 45.

36 Ibid, at 46.

37 See D’Amato, loc. cit. note 13 above, and also the many examples given in Baxter, , “Multilateral Treaties as Evidence of Customary International Law,” 41 Brit. Yr. Bk. Int. Law 275 (1965-1966). In “The Treaty as a Law-Declaring and Custom- Making Instrument,” 22 Egyptian Rev. Int. Law 51, 73-74 (1966), Dr. Shihata claims that state practice with respect to the exemption from capture as prize of war of coastal fishing vessels did not originate in treaties. However, a closer reading of the case he cites to prove this point, The Paquete Habana, 175 U.S. 677, 687 (1900), clearly demonstrates the contrary. The first two precedents in that case were treaties concluded between the monarchs of France and England in 1403 and 1521, recited in orders of the King of England as authority for his implementing legislation.

38 Nottebohm Case, Second Phase, [1955] I.C.J. Rep. 4, 22-23 (Bancroft treaties, Pan American Convention of 1906, and Hague Convention of 1930, the only specific references to any precedent in the entire opinion, and all not involving the parties to the case); Anglo-Norwegian Fisheries Case, [1951] I.C.J. Rep. 116, 131 (treaties and conventions divided as to ten-mile rule for bays); S.S. Wimbledon, P.C.I.J., Ser. A, No. 1, at 15, 28 (1923) (Suez and Panama treaties as precedents for a customary law of interpretation of the Versailles Treaty); International Commission of the Oder, P.C.I.J., Ser. A, No. 23, at 5, 27 (1929) (international river law developed by “subsequent conventions”); Mavrommatis Case, P.C.I.J., Ser. A, No. 2, at 6, 35 (1924) (arbitration treaties used for a customary law of treaty-interpretation for the Mandate treaty in the case).

39 Baxter, loc. cit. note 37 above.

40 Ibid. at 290. It may be noted that, although Professor Baxter seems to confine his remarks to multilateral conventions, no substantive distinction is offered between those and bilateral treaties. It would not seem that a bilateral treaty is different in kind from a multilateral treaty; only the number of parties is smaller. The Bancroft treaties, cited in the Nottebohm Case, note 38 above, were a series of bilateral treaties containing substantially similar provisions.

41 Second Phase, [1955] I.C.J. Rep. 4.

42 See D’Amato, , “Wanted: A Comprehensive Theory of Custom in International Law,” 4 Texas Int. Law Forum 28, 36-40 (1968).


Full text views

Total number of HTML views: 0
Total number of PDF views: 0 *
Loading metrics...

Abstract views

Total abstract views: 0 *
Loading metrics...

* Views captured on Cambridge Core between <date>. This data will be updated every 24 hours.

Usage data cannot currently be displayed