The International Court of Justice and Customary International Law: A Reply to Stefan Talmon

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There is much to agree with in Professor Talmon’s article, which addresses the International Court of Justice’s methodology for the determination of rules of customary international law, and concludes that “the main method employed by the Court is neither induction nor deduction but, rather, assertion.” But there are some questionable aspects, including its conclusion.

The Court’s approach to the identification of rules of customary international law

Professor Talmon regrets the lack of discussion, both by the Court itself and by writers, of the methodology used by the Court to determine the existence, content and scope of rules of customary international law. But the Court has of course stated in its 2012 Jurisdictional Immunities of the State judgment that in order to determine the existence of a rule of customary international law “it must apply the criteria which it has repeatedly laid down for identifying a rule of customary international law” – as indeed it has. The Court recalls its pronouncements in the North Sea Continental Shelf and Continental Shelf (Libyan Arab Jamahiriya/Malta) cases, where it “made clear” that “the existence of a rule of customary international law requires that there be “a settled practice” together with opinio juris” (I.C.J. Reports 2012, p. 99, at p. 122, para. 55). It could well have cited to other decisions as well, among them Military and Paramilitary Activities in and against Nicaragua and Legality of the Threat or Use of Nuclear Weapons. A coherent methodology does come into sight in these (individually and even more so in the aggregate), even if not all questions relating to it have been fully addressed. It is one thing to suggest, as some have, that the Court does not consistently adhere to this stated methodology; it is a different thing altogether to argue, as Professor Talmon does, that the Court “has hardly ever stated” such methodology.

Writers, too – as some of Professor Talmon’s own footnotes suggest – have not left the question of the Court’s methodology untouched. Alvarez-Jiménez’s “Methods for the Identification of Customary International Law in the International Court of Justice’s Jurisprudence: 2000-2009” (cited at Talmon’s n. 24), Geiger’s “Customary International Law in the Jurisprudence of the International Court of Justice: A Critical Appraisal”, Ferrer Lloret’s “The unbearable lightness of customary international law in the jurisprudence of the International Court of Justice”, Hagemann’s “Die Gewohnheit als Völkerrechtsquelle in der Rechtssprechung des internationalen Gerichtshofes” (Schweiz. Jahrb. X,1953, 61 — 88), Benvenisti’s “Customary International Law as a Judicial Tool for Promoting Efficiency”, and most recently Tams’s “Meta-Custom and the Court: A Study in Judicial Law-Making”, to name but a few – all these attest that the Court’s methodology has attracted far more than “little interest”.

The work of the International Law Commission (ILC) on the topic Identification of customary international law shows, moreover, that indeed a good deal can be deduced (more on this rather innocent word below) from a careful reading of the judgments and advisory opinions of the ICJ (and the PCIJ). Certain separate and dissenting opinions of the judges, and several of their extra-judicial writings, are valuable in this respect as well. It is a pity that Professor Talmon’s article appears to have been finalized in July 2014, so understandably no account is taken of the ILC’s work in 2014 and 2015. By July 2015 this had resulted in a set of 16 draft conclusions provisionally adopted by the Drafting Committee, drawing heavily on case-law of the International Court.

Induction v. deduction

Professor Talmon provides his own definitions for ‘inductive’ and ‘deductive’ methods, but then complains of the Court’s “inconsistent and non-technical use of induction and deduction.” In fact, it is not at all clear that the Court ever applies a truly ‘deductive’ method to the determination of customary international law. In any event, the Court itself does not use abstract terms, such as ‘induction’ and ‘deduction’, to describe what it does. It does not engage in theoretical speculation; no amount of strained parsing of various occasional formulations or reliance on a few fleeting references can change that.

No importance attaches to the Court’s occasional use of the word ‘deduce’, which in a plain English simply means ‘reach a conclusion’. (It is thus a little unfair to refer, as Professor Talmon does, to “the Court’s peculiar and untechnical use of the term ‘deduce’”.) Paragraph 94 of Barcelona Traction is scarcely a reference to a ‘deductive method’ for the determination of rules of customary international law. Professor Talmon likewise relies rather heavily on the words ‘can be’ in paragraph 111 of the judgment of the Chamber of the International Court in Gulf of Maine. But that paragraph does not suggest that the Court sometimes adopts a deductive method. It makes a different (if not entirely convincing) point, distinguishing ‘fundamental norms’ from rules of customary international law. The French text of the Judgment (the authoritative text, whatever that may signify) does not have any equivalent of the words ‘can be’; it refers simply to “une série de règles coutumières dont la présence dans l’opinio juris des États se prouve par voie d’induction en partant de l’analyse d’une pratique suffisamment étoffée et convaincante, et non pas par voie de déduction en partant d’idées préconstituées à priori.” That is to say, induction ‘yes’, deduction ‘no’.

Professor Talmon’s analysis does not, moreover, distinguish between cases where the Court has explicitly referred to rules of customary international law, and cases where it may well have resorted to other sources of law (indeed the Court itself does not always make such distinction clear). Unqualified reliance on the Court’s references to rules and principles of general international law that were not clearly applied as custom, does not assist the thesis that the Court determines rules of customary international law through deductive reasoning in order to avoid a non liquet.


Unlike induction and deduction, assertion is self-evidently not a methodology for determining the existence of a rule of customary international law. It is essentially a way of drafting a judgment, a way of stating a conclusion familiar to lawyers working in certain national systems.

As if to reply to Professor Talmon, Judge Tomka has explained in an important address given when he was President of the International Court that

“… authors are correct in drawing attention to the prevalent use of general statements of rules in the Court’s modern practice, although they take the point too far by insisting on theorizing this development. In fact, the Court has never abandoned its view, firmly rooted in the wording of the Statute, that customary international law is “general practice accepted as law”—that is, in the words of a recent case, that “the existence of a rule of customary international law requires that there be a ‘settled practice’ together with opinio juris”. However, in practice, the Court has never found it necessary to undertake such an inquiry for every rule claimed to be customary in a particular case and instead has made use of the best and most expedient evidence available to determine whether a customary rule of this sort exists. Sometimes this entails a direct review of the material elements of custom on their own, while more often it will be sufficient to look to the considered views expressed by States and bodies like the International Law Commission as to whether a rule of customary law exists and what its content is, or at least to use rules that are clearly formulated in a written expression as a focal point to frame and guide an inquiry into the material elements of custom.”

This ‘pragmatic’ approach has recently been sternly criticised, for lack of rigour, by Professor Sienho Yee, Special Rapporteur of an AALCO Informal Expert Group, who has proposed that the following ‘command’ be added at the end of the ILC’s current draft conclusion 2 [3]: “In the identification of customary international law, a rigorous and systematic approach shall be applied.” With respect, the criticism is unjustified. A ‘rigorous and systematic approach’ does not preclude the ‘pragmatic’ approach in appropriate cases, for example where the written text relied upon by the Court is itself the result of a rigorous and systematic review of practice and acceptance as law, and as such has met with the general acceptance of States.

Some bold statements

Beyond this, there are some bold assertions in the article that may raise an eyebrow or two, each of which could be the subject of a posting in its own right. These include the following:

  • “the fact that determining the law also always means developing and, ultimately, creating the law.”
  • “there are certain situations in which the inductive method is impossible to use. Four such situations may be identified…. If induction were the only method for ascertaining the rules of customary international law, the court would have to pronounce a non liquet whenever the inductive method was practically impossible to apply (and treaty rules or general principles were inapplicable).”
  • “a logical rule requires a smaller pool of state practice and opinio juris.”
  • “The inductive method is, however, just as subjective, unpredictable and prone to law creation by the Court as the deductive method.”
  • “There is no greater danger of law creation in deduction than there is in induction.”
  • “The gateway for judicial legislation is neither induction nor deduction but, rather, the ICJ’s use of assertion as a method to determine the rules of customary international law.”
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