Customary International Law

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Determining Customary International Law: The ICJ’s Methodology and the Idyllic World of the ILC

Editor's Note: This is the author's concluding post in the EJIL:Debate! regarding an article in the current issue of EJIL Vol. 26 (2015) No 2, by Stefan Talmon. The original post is here. See also the posts discussing the article by Omri Sender and Michael Wood, Harlan G. Cohen and Fernando Lusa Bordin. I am very grateful to Sir Michael Wood and Omri Sender, as well as Harlan G. Cohen and Fernando Lusa Bordin, for their thoughtful comments on my EJIL article. Both Harlan and Fernando seem to agree with my main propositions and, in particular, with the proposition that the ICJ, in order to determine rules of customary international law, uses induction and deduction as well as assertion. They raise interesting questions that I did not address in my article, such as why the ICJ was not more interested in developing a clear methodology and why States might actually prefer ‘methodological mayhem’, or the flexibility of methodological uncertainty, over…

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Induction, Assertion and the Limits of the Existing Methodologies to Identify Customary International Law

Professor Talmon’s article on the methodologies employed by the International Court of Justice to ascertain custom is as important as it is timely now that the International Law Commission is advancing with its study on the identification of customary international law. To contribute to the debate, I propose to elaborate on a crucial question that the…

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Methodology and Misdirection: Custom and the ICJ

In Determining Customary International Law: The ICJ's Methodology between Induction, Deduction and Assertion, Stefan Talmon revisits the old debate over inductive and deductive methods for finding customary international law (CIL) to see whether we can now, fifty years after the original debates, learn any lessons about whether, when, and how the International Court of Justice uses each.

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

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…

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Determining Customary International Law: The ICJ’s Methodology between Induction, Deduction and Assertion

Methodology is probably not the strong point of the International Court of Justice (ICJ) or, indeed, of international law in general. Unlike its approach to methods of treaty interpretation, the ICJ has hardly ever stated its methodology for determining the existence, content and scope of the rules of customary international law that it applies. There are only isolated…

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