CHICAGO JoHN M. OLIN LAW EcoNoMIcs WORKINg PAPer no. 63 (2D SERIES) A Theory of Customary International Law Jackl. goldsmith and eric A. Posner THE LAW SCHOOL THE UNIVERSITY OF CHICAGO This paper can be downloaded without char The Chicago Working Paper Series Index http://www.lawuchicago.edu/publicatIons/working/index.html The Social Science Research Network Electronic Paper Collection http://papers.ssrn.com/paper.taf?abstract_id=145972
This paper can be downloaded without charge at: The Chicago Working Paper Series Index: http://www.law.uchicago.edu/Publications/Working/index.html The Social Science Research Network Electronic Paper Collection: http://papers.ssrn.com/paper.taf?abstract_id=145972 CHICAGO JOHN M. OLIN LAW & ECONOMICS WORKING PAPER NO. 63 (2D SERIES) A Theory of Customary International Law Jack L. Goldsmith and Eric A. Posner THE LAW SCHOOL THE UNIVERSITY OF CHICAGO
A Theory of Customary International Law Jackl. Goldsmithand eric A. Posner*e Customary international law ("CIL")is one of two primary forms of international law, the other being the treaty. CIL is typically defined as a"customary practice of states followed from a sense of legal obligation. "1 Conventional wisdom views CiL as a unitary phenomenon that pervades international law and international relations. Governments take care to comply with CiL and often incorporate its norms into domestic statutes. National courts apply CIL as a rule of decision, or a defense, or a canon of statutory construction. Nations argue about whether certain acts violate CIL. Violations of CIl are grounds for war or an international claim. Legal commentators view cil to be at the core of the study of international law And yet CIL remains an enigma. 2 It lacks a centrali lawmaker. a centralized executive enforcer. and a centralized authoritative decision-maker. The content of cil seems to track the nterests of powerful nations. The origin of CIl rules is not understood. We do not know why nations comply with CIL,or even what it means for a nation to comply with CIL. and we lack an explanation for the many changes in CIL rules over time. Both parts Associate Professor of Law, University of Chicago Professor of Law, University of Chicago. Thanks to Jaqueline Bhabha, Richard Epstein, Tracey Meares, Richard Ross, Cass Sunstein, Doug Sylvester, Adrian Vermeule, and participants at a workshop at the University of Chicago Law School for comments, and to Christopher Chow, Kyle gehrmann and Kathryn Walsh for research assistance I Restatement(Third)of the Foreign Relations Law of the United States S 102(2) (1986) 2 See G.J. H. van Hoof, Rethinking the Sources of International Law 176-178 (1983)("confusion and divergence of opinion... reign supreme as far as [Cil] is concerned"); David P. Fidler, Challenging the Classical Concept of Custom Perspectives on the Future of Customary International Law, 39 Ger. Y B. Int'l L. 198, 198(1997)("CIL stands at the heart of modern international law while generating frustration and frictions in its identification and application. CIL appears indispensable and incomprehensible.
A Theory of Customary International Law Jack L. Goldsmith* and Eric A. Posner** Customary international law (“CIL”) is one of two primary forms of international law, the other being the treaty. CIL is typically defined as a “customary practice of states followed from a sense of legal obligation.”1 Conventional wisdom views CIL as a unitary phenomenon that pervades international law and international relations. Governments take care to comply with CIL, and often incorporate its norms into domestic statutes. National courts apply CIL as a rule of decision, or a defense, or a canon of statutory construction. Nations argue about whether certain acts violate CIL. Violations of CIL are grounds for war or an international claim. Legal commentators view CIL to be at the core of the study of international law. And yet CIL remains an enigma.2 It lacks a centralized lawmaker, a centralized executive enforcer, and a centralized, authoritative decision-maker. The content of CIL seems to track the interests of powerful nations. The origin of CIL rules is not understood. We do not know why nations comply with CIL, or even what it means for a nation to comply with CIL. And we lack an explanation for the many changes in CIL rules over time. Both parts * Associate Professor of Law, University of Chicago. ** Professor of Law, University of Chicago. Thanks to Jaqueline Bhabha, Richard Epstein, Tracey Meares, Richard Ross, Cass Sunstein, Doug Sylvester, Adrian Vermeule, and participants at a workshop at the University of Chicago Law School for comments, and to Christopher Chow, Kyle Gehrmann and Kathryn Walsh for research assistance. 1 Restatement (Third) of the Foreign Relations Law of the United States § 102(2) (1986). 2 See G.J.H. van Hoof, Rethinking the Sources of International Law 176-178 (1983) (“confusion and divergence of opinion . . . reign supreme as far as [CIL] is concerned”); David P. Fidler, Challenging the Classical Concept of Custom: Perspectives on the Future of Customary International Law, 39 Ger. Y.B. Int’l L. 198, 198 (1997) (“CIL stands at the heart of modern international law while generating frustration and frictions in its identification and application. CIL appears indispensable and incomprehensible.”)
CHICAGO WORKING PAPER IN LAW AND ECONOMICS of CiL's standard definition raise perennial, and unanswered, uestions. It is unclear which state acts count as evidence of a custom, or how broad or consistent state practice must be to satisfy the custom requirement. It is also unclear what it means for a nation to follow a custom from a sense of legal obligation, or how one determines whether such an obligation exist This article presents a theory of Cil that seeks to sort out these and many other difficulties with the standard account of CIl. The theory uses simple game theoretical concepts to explain how what we call CIL arises, why nations" comply"with CIL as commonly understood, and how CIL changes. 3 After briefly describing conventional wisdom about CIL in Section I, Section II presents the theory. This theory views the behaviors that are traditionally thought to constitute a unitary CIL as variations of one of four different behavioral logics. First, some of what is called CiL is better thought of as behavior arising from coincidence of interest, where behavioral regularities result from the orivate advantage each state obtains from the same action regardless of the action of the other. Second some of what is called cil is better thought of as arising from coercion, where a powerful state(or 3 Our approach has many affinities with the rational choice school in international relations. See Cooperation Under Anarchy(ed. Kenneth Oye 1986): Jame Morrow, Modeling the Forms of International Cooperation: Distribution Versus Information, 48 Int'l Org. 387(1994); Duncan Nidal, Coordination Versus Prisoners Dilemma: Implications for International Cooperation, 79 Am. PoL. S Rev. 923(1985). In recent years international law scholarship has begun to borrow heavily from the international relations literature. See Anne-Marie Slaughter, et al.. International law and international relations: a New generation of Interdisciplinary Scholarship, 92 Am. J. Int'l L. 367(1998)(survey): Jeffrey Dunhoff Joel Trachtman, Economic Analysis of International Law: An Invitation and a Caveat(forthcoming)(different survey). However, this literature ontains no theory of CIL, a huge gap considering the fundamental role of CIL in international law. There has been no comprehensive analysis of customary international law through the lens of rational choice, game theory, and related approaches. See Dunhoff Trachtman, supra, at_(appendix). Michael Byers onstructivist school of international IL that differs from ours in methodology and conclusion. See Michael Byers, Custom, Power, and the Power of Rules, 17 Mich. J. Int'l L. 109(1995) Fernando Teson briefly sketches a game-theoretic account of CIL in order to criticize it on positive and especially normative grounds. See Fernando Teson, A Philosophy of International Law 74-77(1998)
CHICAGO WORKING PAPER IN LAW AND ECONOMICS 2 of CIL’s standard definition raise perennial, and unanswered, questions. It is unclear which state acts count as evidence of a custom, or how broad or consistent state practice must be to satisfy the custom requirement. It is also unclear what it means for a nation to follow a custom from a sense of legal obligation, or how one determines whether such an obligation exists. This article presents a theory of CIL that seeks to sort out these and many other difficulties with the standard account of CIL. The theory uses simple game theoretical concepts to explain how what we call CIL arises, why nations “comply” with CIL as commonly understood, and how CIL changes.3 After briefly describing conventional wisdom about CIL in Section I, Section II presents the theory. This theory views the behaviors that are traditionally thought to constitute a unitary CIL as variations of one of four different behavioral logics. First, some of what is called CIL is better thought of as behavior arising from coincidence of interest, where behavioral regularities result from the private advantage each state obtains from the same action regardless of the action of the other. Second, some of what is called CIL is better thought of as arising from coercion, where a powerful state (or 3 Our approach has many affinities with the rational choice school in international relations. See Cooperation Under Anarchy (ed. Kenneth Oye 1986); James Morrow, Modeling the Forms of International Cooperation: Distribution Versus Information, 48 Int’l Org. 387 (1994); Duncan Snidal, Coordination Versus Prisoners’ Dilemma: Implications for International Cooperation, 79 Am. Pol. Sc. Rev. 923 (1985). In recent years international law scholarship has begun to borrow heavily from the international relations literature. See Anne-Marie Slaughter, et al., International Law and International Relations: A New Generation of Interdisciplinary Scholarship, 92 Am. J. Int’l L. 367 (1998) (survey); Jeffrey Dunhoff & Joel Trachtman, Economic Analysis of International Law: An Invitation and a Caveat (forthcoming) (different survey). However, this literature contains no theory of CIL, a huge gap considering the fundamental role of CIL in international law. There has been no comprehensive analysis of customary international law through the lens of rational choice, game theory, and related approaches. See Dunhoff & Trachtman, supra, at __ (appendix). Michael Byers draws on the constructivist school of international relations to gives an account of CIL that differs from ours in methodology and conclusion. See Michael Byers, Custom, Power, and the Power of Rules, 17 Mich. J. Int’l L. 109 (1995). Fernando Teson briefly sketches a game-theoretic account of CIL in order to criticize it on positive and especially normative grounds. See Fernando Teson, A Philosophy of International Law 74-77 (1998)
CUSTOMARY INTERNATIONAL LAW coalition of states with convergent interests) forces or threatens to force other states to engage in acts that they would not do in the absence of such force. Although we take no position on how the labelCiL "ought to be used, scholars who use this label to refer to behavior arising from coincidence of interest or coercion usually are under the erroneous impression that the behavior reflects successful international cooperation Third are cases of true cooperation. These cases are best modeled as a bilateral iterated prisoners dilemma in which two states receive relatively high payoffs over the long term as long as both states resist the temptation to cheat in the short term If certain conditions are met, the resulting behavioral regularity can be one in which the higher payoffs are obtained. Fourth, some behavioral regulariti associated with CIL can arise when states face and solve bilateral coordination problems. In these cases, states receive higher payoffs if they take identical or symmetrical actions than if they do not. Both cooperation and coordination can be robust in bilateral contexts, but will not likely occur in multilateral contexts The theory suggests that most international behavioral regularities associated with CIL reflect coincidence of interest or coercion. These cases are trivial and have no normative content for states independently pursue their self-interest without generating gains from interaction. The theory also contemplates that some international behavioral regularities associated with CIL will reflect cooperation or coordination, but the theory suggests that these egularities will arise in bilateral, not multilateral, interactions. What appear to be multilateral CIL norms, then, are illusions, the product of some combination of (a) coincidence of interests among all, or almost all, states, (b)coercion by one or a few powerful states, or(c) a prisoner's dilemma or a coordination game played out in discrete bilateral contexts This theory differs from the standard conception of CIL in several fundamental respects It rejects the usual explanations of CIL based on opinio juris legality, morality, and related concepts. States do not comply with norms of Cil because of a sense of moral or legal obligation; rather, their compliance and the norms themselves emerge from the states pursuit of self-interested policies on the international stage. In other words, CiL is not an exogenous force
3 CUSTOMARY INTERNATIONAL LAW coalition of states with convergent interests) forces or threatens to force other states to engage in acts that they would not do in the absence of such force. Although we take no position on how the label “CIL” ought to be used, scholars who use this label to refer to behavior arising from coincidence of interest or coercion usually are under the erroneous impression that the behavior reflects successful international cooperation. Third are cases of true cooperation. These cases are best modeled as a bilateral iterated prisoner’s dilemma in which two states receive relatively high payoffs over the long term as long as both states resist the temptation to cheat in the short term. If certain conditions are met, the resulting behavioral regularity can be one in which the higher payoffs are obtained. Fourth, some behavioral regularities associated with CIL can arise when states face and solve bilateral coordination problems. In these cases, states receive higher payoffs if they take identical or symmetrical actions than if they do not. Both cooperation and coordination can be robust in bilateral contexts, but will not likely occur in multilateral contexts. The theory suggests that most international behavioral regularities associated with CIL reflect coincidence of interest or coercion. These cases are trivial and have no normative content, for states independently pursue their self-interest without generating gains from interaction. The theory also contemplates that some international behavioral regularities associated with CIL will reflect cooperation or coordination, but the theory suggests that these regularities will arise in bilateral, not multilateral, interactions. What appear to be multilateral CIL norms, then, are illusions, the product of some combination of (a) coincidence of interests among all, or almost all, states, (b) coercion by one or a few powerful states, or (c) a prisoner’s dilemma or a coordination game played out in discrete bilateral contexts. This theory differs from the standard conception of CIL in several fundamental respects. It rejects the usual explanations of CIL based on opinio juris, legality, morality, and related concepts. States do not comply with norms of CIL because of a sense of moral or legal obligation; rather, their compliance and the norms themselves emerge from the states’ pursuit of self-interested policies on the international stage. In other words, CIL is not an exogenous force
CHICAGO WORKING PAPER IN LAW AND ECONOMICS that controls the behavior of states; it is a label people attach to behavior that is generated endogenously from the interactions of states pursuing their self-interest. In addition, our theory rejects the traditional claim that the behaviors associated with cil reflect a single unitary logic. These behaviors instead reflect various and importantly different logical structures played out in discrete, historically contingent contexts. Finally, the theory is skeptical of the existence of law-like, multilateral behavioral regularities that are typically thought to constitute CIL. It holds that multinational regularities will invariably reflect coincidence of interest or coercion (and thus not be law-like), and that regularities that reflect cooperation or coordination arise only in bilateral contexts Section III tests the theory using case studies from four traditional areas of CIL: neutrality, diplomatic immunity, prize, and maritime jurisdiction. We chose to study these areas of the law because they represent a broad spectrum of CIL norms, and becaus these CIL norms are, according to conventional accounts, among the most robust that exist. The case studies teach several lessons The nain lesson is that cil as traditionally understood has little explanatory power. The international behaviors said to constitute CIL are actually disparate and changing practices that follow different logics depending on the interaction of state interests in rticular contexts. The case studies suggest that the behaviors associated with Cil do not reflect a unitary underlying logic, and hat Cil understood as a normative force does no independent work in guiding national behavior. The case studies als so reveal how commentators and courts commit errors of induction in moving from the observation of a behavioral regularity to the conclusion that a CiL rule exists. In addition, in analyzing CIL courts and commentators rely too heavily on what nations say at the expense of what they do and why they do it, and they tend to limit cil to behavioral regularities that are good"from their normative perspective to be CIL, denigrating regularities that are bad as comity"or a violation or an exception to the CIL rule. Finally, the case studies confirm that cil does not reflect multilateral, law-like behavioral regularities Section IV considers several extensions of the analysis. It unpacks the artificial assumption of a unitary state interest that lies
CHICAGO WORKING PAPER IN LAW AND ECONOMICS 4 that controls the behavior of states; it is a label people attach to behavior that is generated endogenously from the interactions of states pursuing their self-interest. In addition, our theory rejects the traditional claim that the behaviors associated with CIL reflect a single, unitary logic. These behaviors instead reflect various and importantly different logical structures played out in discrete, historically contingent contexts. Finally, the theory is skeptical of the existence of law-like, multilateral behavioral regularities that are typically thought to constitute CIL. It holds that multinational regularities will invariably reflect coincidence of interest or coercion (and thus not be law-like), and that regularities that reflect cooperation or coordination arise only in bilateral contexts. Section III tests the theory using case studies from four traditional areas of CIL: neutrality, diplomatic immunity, prize, and maritime jurisdiction. We chose to study these areas of the law because they represent a broad spectrum of CIL norms, and because these CIL norms are, according to conventional accounts, among the most robust that exist. The case studies teach several lessons. The main lesson is that CIL as traditionally understood has little explanatory power. The international behaviors said to constitute CIL are actually disparate and changing practices that follow different logics depending on the interaction of state interests in particular contexts. The case studies suggest that the behaviors associated with CIL do not reflect a unitary underlying logic, and that CIL understood as a normative force does no independent work in guiding national behavior. The case studies also reveal how commentators and courts commit errors of induction in moving from the observation of a behavioral regularity to the conclusion that a CIL rule exists. In addition, in analyzing CIL courts and commentators rely too heavily on what nations say at the expense of what they do and why they do it, and they tend to limit CIL to behavioral regularities that are “good” from their normative perspective to be CIL, denigrating regularities that are bad as “comity” or a violation or an exception to the CIL rule. Finally, the case studies confirm that CIL does not reflect multilateral, law-like behavioral regularities. Section IV considers several extensions of the analysis. It unpacks the artificial assumption of a unitary state interest that lies