Uncertainty in the Formal Sources of International Law: Customary International Law and Some of its Problems

Posted: 29 Feb 2008 Last revised: 6 Feb 2013

See all articles by Jörg Kammerhofer

Jörg Kammerhofer

University of Freiburg - Faculty of Law

Date Written: June 1, 2004


Uncertainty abounds in international law and customary international law is no exception. This article seeks to delineate this uncertainty and explain its causes. Not only is there uncertainty surrounding the exact nature of the two elements considered necessary for custom-formation - state practice and opinio juris - we also do not know how custom-formation works. It is not clear what precisely 'state practice' is, nor do we know how we can have a belief that something is already law in order to create it. The particular uncertainties of customary international law point directly to systemic uncertainties at a higher level. Article 38 of the Statute of the International Court of Justice is convenient, but is it authoritative? What is the basis of our knowledge regarding customary law-making? This article argues that two commonly used approaches to provide a theoretical underpinning - deduction and induction - are fundamentally flawed in their pure forms. Their problems are alleviated, but not solved, by combining them. Without a dominant legal culture and without a written constitution to blind us to other possibilities, not even a pragmatic outlook can save us from uncertainty. However, even where the law is not disputed, it remains an ideal, not real. Law is based on the fiction that it exists.

Keywords: Customary international law, opinio juris, state practice, evidence, sources of international law, Hans Kelsen, Pure Theory of Law

Suggested Citation

Kammerhofer, Jörg, Uncertainty in the Formal Sources of International Law: Customary International Law and Some of its Problems (June 1, 2004). European Journal of International Law, Vol. 15, pp. 523-553, 2004, Available at SSRN: https://ssrn.com/abstract=803752

Jörg Kammerhofer (Contact Author)

University of Freiburg - Faculty of Law ( email )

D-79098 Freiburg

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