The Customary International Law Game


Structural realists in political science and some rationalist legal scholars argue that customary international law cannot affect state behavior: that it is “epiphenomenal.” This article develops a game theoretic model of a multilateral prisoner’s dilemma in the customary international law context that shows that it is plausible that states would comply with customary international law under certain circumstances. Our model shows that these circumstances relate to: (i) the relative value of cooperation versus defection, (ii) the number of states effectively involved, (iii) the extent to which increasing the number of states involved increases the value of cooperation or the detriments of defection, including whether the particular issue has characteristics of a commons problem, a public good, or a network good, (iv) the information available to the states involved regarding compliance and defection, (v) the relative patience of states in valuing the benefits of long-term cooperation compared to short-term defection, (vi) the expected duration of interaction, (vii) the frequency of interaction, and (viii) whether there are also bilateral relationships or other multilateral relationships between the involved states.

This model shows that customary international law is plausible in the sense that it may well affect state behavior where certain conditions are met. It shows what types of contexts, including malleable institutional features, may affect the ability of states to produce and comply with customary international law. This article identifies a number of empirical strategies that may be used to test the model.


International Law | International Trade Law | Law and Economics | Law and Society

Date of this Version

April 2005