Customary International Law

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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 piece raises. Why is it that the Court so often resorts to ‘asserting’ customary international law instead of providing more robust reasoning to back up the rules that it identifies? Though the precise reasons why the Court takes the approach it does are a matter for speculation, I suspect that this has to do with limitations that are inherent to the standard methodology to establish custom (the ‘inductive method’, to use Professor Talmon’s terminology), in the shaping of which the Court itself has played a large part. As Professor Talmon suggests, systemic reasoning – argument by principle and argument by analogy – has been a major catalyst for development in international law, filling gaps that would…

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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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