An Experimental Contribution to the Theory of Customary (International) Law

23 Pages Posted: 5 May 2010

See all articles by Christoph Engel

Christoph Engel

Max Planck Society for the Advancement of the Sciences - Max Planck Institute for Research on Collective Goods; University of Bonn - Faculty of Law & Economics; Erasmus University Rotterdam (EUR), Erasmus School of Law, Rotterdam Institute of Law and Economics, Students; Universität Osnabrück - Faculty of Law

Date Written: April 2010

Abstract

In their majority, public international lawyers postulate that for a new rule of customary law to originate, two conditions must be fulfilled: there must be consistent practice, and it must be shown that this practice is motivated by the belief that such behaviour is required in law. Maurice Mendelson (Recueil des Cours 272 (1998) 155) has challenged this view. He believes that the majority view ignores the fundamentally incomplete nature of public international law. He claims that the new rule emerges because mere practice leads to convergent expectations. This paper uses data from student experiments with a linear public good to show that behaviour converges even absent verbal communication; that convergence is guided by mean contributions in the previous round, which serve as an implicit norm; that freeriding on this implicit norm is regarded as illegitimate; that cooperation can be stabilised at a high level if “reprisals” are permitted. Hence the mechanism of norm formation proposed by Maurice Mendelson is fully borne out by the experimental data.

Keywords: customary international law, opinio iuris, experiment, linear public good

JEL Classification: C91, D03, D23, F53, H41, K33

Suggested Citation

Engel, Christoph, An Experimental Contribution to the Theory of Customary (International) Law (April 2010). MPI Collective Goods Preprint, No. 2010/13, Available at SSRN: https://ssrn.com/abstract=1599464 or http://dx.doi.org/10.2139/ssrn.1599464

Christoph Engel (Contact Author)

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Universität Osnabrück - Faculty of Law

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