23 February 2004 The Customary International Law Supergame Order and law George Norman Joel P. trachtman Abstract Customary international law is an enigma. It is produced by the decentralized actions of states, and it generally lacks centralized enforcement mechanisms. Political science realists and some rationalist legal scholars argue that customary international law cannot affect state behavior: that it is"epiphenomenal. This article develops a model of an n-player 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. 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, (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 One implication of this model is to lend credence to customary international law From a research standpoint, this model identifies a number of parameters for which data may be developed in order to test the model. From a policy standpoint, this model shows what types of contexts, including malleable institutional features, may affect the ability of states to reach stable and efficient equilibria in their customary international law William and Joyce Cummings Professor of Entrepreneurship and Business Economics Tufts University Professor of International Law, The Fletcher School of Law and Diplomacy, Tufts o George Norman and Joel Trachtman. All rights reserved. Preliminary draft. Please do not cite or further circulate without the authors permission
23 February 2004 George Norman * Joel P. Trachtman ** Abstract Customary international law is an enigma. It is produced by the decentralized actions of states, and it generally lacks centralized enforcement mechanisms. Political science realists and some rationalist legal scholars argue that customary international law cannot affect state behavior: that it is “epiphenomenal.” This article develops a model of an n-player 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. 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, (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. One implication of this model is to lend credence to customary international law. From a research standpoint, this model identifies a number of parameters for which data may be developed in order to test the model. From a policy standpoint, this model shows what types of contexts, including malleable institutional features, may affect the ability of states to reach stable and efficient equilibria in their customary international law relations. * William and Joyce Cummings Professor of Entrepreneurship and Business Economics, Tufts University. ** Professor of International Law, The Fletcher School of Law and Diplomacy, Tufts University. © George Norman and Joel Trachtman. All rights reserved. Preliminary draft. Please do not cite or further circulate without the authors’ permission. The Customary International Law Supergame: Order and Law
The Customary International Law Supergame February 23, 2004 1. Introduction Customary international law( CIL) forms the infrastructure of international lay and is also part of international laws superstructure. It thus serves as its own foundation but also as the foundation for treaty law, and therefore for essentially all international law. How firm is this foundation CIL Seems to have fallen on hard times, as it has been overtaken by treaty as the principal source of new rules in the international community, as it often seems to be used by idealists to make boot-strapping arguments about the content of international law, and as its binding force---its social effect--is often not readily apparent. This at a time when the domestic analog of CIL-social norms---is the darling of legal scholarship CiL is under attack as behaviorally epiphenomenal and doctrinally incoherent By contrast, the central argument of this article is that CIL, while something of a trick of levitation, is theoretically plausible. Our argument makes one central claim: that while there are limits on and variations in the effectiveness of cil. there are circumstances where it may independently affect the behavior of states. There is no reason in theory, or in data adduced by others, to believe CiL generally epiphenomenal. In addition, as a by- product of the analysis supporting our central claim, we find that the cil doctrine that has developed in order to discriminate between valid and invalid assertions of the existence of rules of CiL is internally coherent, and consistent with our models rationalist perspective on state behavior See generally, J. Patrick Kelly, The Twilight of Customary International Law, 40VA J. INTLL.449(2000)
The Customary International Law Supergame February 23, 2004 1 1. Introduction Customary international law (CIL) forms the infrastructure of international law, and is also part of international law’s superstructure. It thus serves as its own foundation, but also as the foundation for treaty law, and therefore for essentially all international law. How firm is this foundation? CIL seems to have fallen on hard times, as it has been overtaken by treaty as the principal source of new rules in the international community, as it often seems to be used by idealists to make boot-strapping arguments about the content of international law, and as its binding force—its social effect—is often not readily apparent. 1 This at a time when the domestic analog of CIL—social norms—is the darling of legal scholarship. CIL is under attack as behaviorally epiphenomenal and doctrinally incoherent. By contrast, the central argument of this article is that CIL, while something of a trick of levitation, is theoretically plausible. Our argument makes one central claim: that while there are limits on and variations in the effectiveness of CIL, there are circumstances where it may independently affect the behavior of states. There is no reason in theory, or in data adduced by others, to believe CIL generally epiphenomenal. In addition, as a byproduct of the analysis supporting our central claim, we find that the CIL doctrine that has developed in order to discriminate between valid and invalid assertions of the existence of rules of CIL is internally coherent, and consistent with our model’s rationalist perspective on state behavior. 1 See generally, J. Patrick Kelly, The Twilight of Customary International Law, 40 VA. J. INT'L L. 449 (2000)
The Customary International Law Supergame February 23, 2004 This article refines and extends an emerging rationalist understanding of CIL Pioneering work in this field, notably that of Jack Goldsmith and Eric Posner, has begun to articulate a rationalist theory of CIL. Goldsmith and posner have argued that CIL(a) does not exogenously affect state behavior and (b) is internally incoherent, as states not motivated by opinio juris to comply with CiL.' We show why the first assertion is either tautological or incorrect as a matter of theory, and, to the extent that it purports to rely on factual observation, is not supported by the data presented. The tautology arises from a false dichotomy between motivation by self-interest and motivation by law. In a ationalist model, behavior is assumed to be motivated by self-interest. If law is artificially separated from self-interest, then of course a rationalist model would assume that law has no motivating force. Yet we show how CiL rules may modify the payoffs of behavior and therefore affect behavior through self-interest. While cil is endogenous to states as a group, it is an exogenous influence on the behavior of each individual state CIL may affect behavior even if it only does so at the margins. As to the second assertion, our analysis provides a plausible basis to assign a discriminating role to opinio juris, and therefore we find cil doctrine internally coherent in at least its core dimension This article develops an iterated multi-player prisoners dilemma model of CIL. Of course, game theory can only provide a crude representation of highly nuanced decision-making. Our analysis focuses on parameters of the multi-player prisoners dilemma in the CIL context: (i)the relative value of cooperation versus defection, (ii) the number of states effectively involved, (iii) the extent to which increasing the number of See, e.g., Mark A Chinen, Afterword, 23 MICH. J INT'L L 201(2001); Mark A Chinen, Game Theory and Customary International Law: A Response to Professors Goldsmith and Posner, 23 MICH. J INT'L L 143 (2001): Vincy Fon francesco Parisi, International Customary Law and Articulation Theories: An Economic Analysis, George Mason Law and Economics Research Paper No. 02-24, available at http:papersssrn.com/sol3/papers.cfm?abstractid=335220;JackL.Goldsmith&ericA Posner, Further Thoughts on Customary International Law, 23 MICH. J INTL L. 191 (2001); Jack L. Goldsmith& Eric A Posner, A Theory of Customary International Law, 66 U. CHI. L REv. 1113(1999) hereinafter Goldsmith Posner 1999]; Andrew T. Guzman, A Compliance-Based Theory of international Law, 90 CAL L REV. 1823 (2002); Francesco Parisi, The Formation of Customary Law, George Mason Law and Economics Research Paper No. O1-06, http:/papers.ssrn.com/sol3/papers.cfm?abstractid=262032;edWardt.SwaineRational Custom, 52: 3 DUKE L.J. 559(2002); Pierre-Hugues Verdier, Cooperative States International Relations, State Responsibility and the Problem of custom, 42 VA L REV 839(2002) he leading article here is goldsmith posner 1999, supra note 2. pcc "self-interest "we mean merely to refer to maximization of preferences--these rences could be other-regarding or altruistic See the cautions expressed in Goldsmith Posner 1999, supra note 2, and the broader treatment in Duncan Nidal, The Game Theory of International Politics, in Kenneth A Oye, ed. COOPERATION UNDER ANARCHY (1986)
The Customary International Law Supergame February 23, 2004 2 This article refines and extends an emerging rationalist understanding of CIL. 2 Pioneering work in this field, notably that of Jack Goldsmith and Eric Posner, has begun to articulate a rationalist theory of CIL. Goldsmith and Posner have argued that CIL (a) does not exogenously affect state behavior and (b) is internally incoherent, as states are not motivated by opinio juris to comply with CIL. 3 We show why the first assertion is either tautological or incorrect as a matter of theory, and, to the extent that it purports to rely on factual observation, is not supported by the data presented. The tautology arises from a false dichotomy between motivation by self-interest 4 and motivation by law. In a rationalist model, behavior is assumed to be motivated by self-interest. If law is artificially separated from self-interest, then of course a rationalist model would assume that law has no motivating force. Yet we show how CIL rules may modify the payoffs of behavior and therefore affect behavior through self-interest. While CIL is endogenous to states as a group, it is an exogenous influence on the behavior of each individual state. CIL may affect behavior even if it only does so at the margins. As to the second assertion, our analysis provides a plausible basis to assign a discriminating role to opinio juris, and therefore we find CIL doctrine internally coherent in at least its core dimension. This article develops an iterated multi-player prisoner’s dilemma model of CIL. Of course, game theory can only provide a crude representation of highly nuanced decision-making. 5 Our analysis focuses on parameters of the multi-player prisoner’s dilemma in the CIL context: (i) the relative value of cooperation versus defection, (ii) the number of states effectively involved, (iii) the extent to which increasing the number of 2 See, e.g., Mark A. Chinen, Afterword, 23 MICH. J. INT'L L. 201 (2001); Mark A. Chinen, Game Theory and Customary International Law: A Response to Professors Goldsmith and Posner, 23 MICH. J. INT'L L. 143 (2001); Vincy Fon & Francesco Parisi, International Customary Law and Articulation Theories: An Economic Analysis, George Mason Law and Economics Research Paper No. 02-24, available at http://papers.ssrn.com/sol3/papers.cfm?abstract_id=335220; Jack L. Goldsmith & Eric A. Posner, Further Thoughts on Customary International Law, 23 MICH. J. INT'L L. 191 (2001); Jack L. Goldsmith & Eric A. Posner, A Theory of Customary International Law, 66 U. CHI. L. REV. 1113 (1999) [hereinafter Goldsmith & Posner 1999]; Andrew T. Guzman, A Compliance-Based Theory of International Law, 90 CAL. L. REV. 1823 (2002); Francesco Parisi, The Formation of Customary Law, George Mason Law and Economics Research Paper No. 01-06, http://papers.ssrn.com/sol3/papers.cfm?abstract_id=262032; Edward T. Swaine, Rational Custom, 52:3 DUKE L.J. 559 (2002); Pierre-Hugues Verdier, Cooperative States: International Relations, State Responsibility and the Problem of Custom, 42 VA. L. REV. 839 (2002). 3 The leading article here is Goldsmith & Posner 1999, supra note 2. 4 By “self-interest” we mean merely to refer to maximization of preferences—these preferences could be other-regarding or altruistic. 5 See the cautions expressed in Goldsmith & Posner 1999, supra note 2, and the broader treatment in Duncan Snidal, The Game Theory of International Politics, in Kenneth A. Oye, ed., COOPERATION UNDER ANARCHY (1986)
The Customary International Law Supergame February 23, 2004 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, (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 The parameters we identify are incorporated in our model as independent variables, but from a normative standpoint it is possible for policy initiatives to select or manipulate these parameters. That is, by developing a positive theory suggesting the parameters for determining whether Cil will affect state behavior, this article opens the way to normative institutional design. States may determine to restructure certain nstitutions in order to facilitate the formation and operation of CiL. There may be circumstances under which it will be normatively attractive to facilitate the development of CIL, rather than to engage in more self-conscious and static treaty-making. The institutional dynamism and social immanence that attracts some scholars to social norms n the domestic context may also be attractive in at least some international contexts This article is organized as follows. The remainder of this introduction provides a short definition of CIL and briefly locates this article in relation to four literatures: law and economics, social norms, international organization and industrial organization. Part 2 explains our choice of the iterated n-person prisoner's dilemma as the basis for our model, as well as our choice of an assumed strategy for players within this model. Part 3 explains the other assumptions and parameters of our model. Part 4 sets forth the formal model. Part 5 presents some implications in terms of (i) the plausibility of CIL, (ii) policy, (iii)international law doctrine, and (iv) research. Part 6 briefly concludes a. Customary International Law and its Doctrine As an introductory matter, it is useful to review the fundamental definition of CIL. Article 102 of the American Law Institutes Restatement (Third) of Foreign Relations Law states that"Customary international law results from a general and consistent practice of states followed by them from a sense of legal obligation. The sense of obligation is referred to in Latin as"opinio juris sive necessitatis. " Articl 38(1(b) of the Statute of the International Court of Justice, listing the sources of international law applicable by the Court, includes"international custom, as evidence of a general practice accepted as law. CiL has two core doctrinal problems relating to opinio juris. First, can CIL ever come into existence if it requires opinio juris-a sense of legal obligation--before it can exist? The second relates to the motivation of states. Are states ever motivated by opinio Daniel A. Farber, Positive Theory as Normative Critique, 68 S CAL L REV. 1565 (1995)
The Customary International Law Supergame February 23, 2004 3 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, (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. The parameters we identify are incorporated in our model as independent variables, but from a normative standpoint it is possible for policy initiatives to select or manipulate these parameters. That is, by developing a positive theory suggesting the parameters for determining whether CIL will affect state behavior, this article opens the way to normative institutional design. 6 States may determine to restructure certain institutions in order to facilitate the formation and operation of CIL. There may be circumstances under which it will be normatively attractive to facilitate the development of CIL, rather than to engage in more self-conscious and static treaty-making. The institutional dynamism and social immanence that attracts some scholars to social norms in the domestic context may also be attractive in at least some international contexts. This article is organized as follows. The remainder of this introduction provides a short definition of CIL and briefly locates this article in relation to four literatures: law and economics, social norms, international organization and industrial organization. Part 2 explains our choice of the iterated n-person prisoner’s dilemma as the basis for our model, as well as our choice of an assumed strategy for players within this model. Part 3 explains the other assumptions and parameters of our model. Part 4 sets forth the formal model. Part 5 presents some implications in terms of (i) the plausibility of CIL, (ii) policy, (iii) international law doctrine, and (iv) research. Part 6 briefly concludes. a. Customary International Law and its Doctrine As an introductory matter, it is useful to review the fundamental definition of CIL. Article 102 of the American Law Institute’s Restatement (Third) of Foreign Relations Law states that “[c]ustomary international law results from a general and consistent practice of states followed by them from a sense of legal obligation.” The sense of obligation is referred to in Latin as “opinio juris sive necessitatis.” Article 38(1)(b) of the Statute of the International Court of Justice, listing the sources of international law applicable by the Court, includes “international custom, as evidence of a general practice accepted as law.” CIL has two core doctrinal problems relating to opinio juris. First, can CIL ever come into existence if it requires opinio juris—a sense of legal obligation—before it can exist? The second relates to the motivation of states. Are states ever motivated by opinio 6 Daniel A. Farber, Positive Theory as Normative Critique, 68 S. CAL. L. REV. 1565 (1995)
The Customary International Law Supergame February 23, 200 juris? The rationalist assumption of states motivated by their own preferences seems prima facie inconsistent with the Cil requirement of motivation by opinio juris, and this is the criticism that Goldsmith and Posner level at CIL doctrine. They argue that what appears to be cil is actually motivated by coincidence of interest, coercion, cooperation predicated on self-interest, or coordination predicated on self-interest. We respond to thi argument in part 5. For the social scientist studying law, the critical descriptive question relates to the effects of legal rules on behavior. For CIL, this descriptive question is also a doctrinal question, as Cil doctrine requires some level of generality and consistency of practice some quantum of state behavior. And again, at least under the restatement formulation, this behavior must be motivated by opinio juris. Under the Statute of the International Court of Justice, the custom itself may serve as evidence of acceptance as law, of opinio juris. Some commentators have suggested that opinio juris in a formal sense may not be necessary at all, but that the requirement should be understood in terms of state consent or acceptance As we address the theory of CIL, it is useful to have in mind some examples CIL. CIL exists in a wide variety of fields, and coexists in many areas with treaty law As already noted, CIL is its own foundation. Thus, there is a CiL of CIL. In other words, the cil doctrine discussed above is understood as law pursuant to CIL Furthermore, the law of treaties came into existence pursuant to CIL, although this law is today codified in treaty. But moving beyond these foundational areas, CIL addresses, for example, issues of territorial integrity, jurisdiction to apply law, diplomatic immunity, the rights of states with respect to coastal areas, human rights, cross-border pollution and the use of force to settle international disputes These are diverse fields. each with its own characteristics. Our theoretical approach calls for discrimination among these fields. The parameters for discrimination are indicated by the model set forth below. Simply put, we would expect greater possibility for formation of and compliance with Cil in some fields than in others. Of course, this is an area in which empiricism would require analysis of areas in which CiL has not developed: the dog that did not bark. Thus, we might ask, why is there no Cl rule that prohibits over-fishing in international waters? Why is there no Cil rule that requires extradition of criminals? Our theoretical approach also accepts the possibility of linkage among diverse fields, integrating and therefore homogenizing the behavioral effect of each rule of law b. Four literatures 7 Goldsmith Posner 1999 .supra note 2 Maurice H Mendelson, The Formation of Customary International Law, 272 RECUEIL DES COURS 155, 268-293(1998)
The Customary International Law Supergame February 23, 2004 4 juris? The rationalist assumption of states motivated by their own preferences seems prima facie inconsistent with the CIL requirement of motivation by opinio juris, and this is the criticism that Goldsmith and Posner level at CIL doctrine. 7 They argue that what appears to be CIL is actually motivated by coincidence of interest, coercion, cooperation predicated on self-interest, or coordination predicated on self-interest. We respond to this argument in part 5. For the social scientist studying law, the critical descriptive question relates to the effects of legal rules on behavior. For CIL, this descriptive question is also a doctrinal question, as CIL doctrine requires some level of generality and consistency of practice— some quantum of state behavior. And again, at least under the Restatement formulation, this behavior must be motivated by opinio juris. Under the Statute of the International Court of Justice, the custom itself may serve as evidence of acceptance as law, of opinio juris. Some commentators have suggested that opinio juris in a formal sense may not be necessary at all, but that the requirement should be understood in terms of state consent or acceptance. 8 As we address the theory of CIL, it is useful to have in mind some examples of CIL. CIL exists in a wide variety of fields, and coexists in many areas with treaty law. As already noted, CIL is its own foundation. Thus, there is a CIL of CIL. In other words, the CIL doctrine discussed above is understood as law pursuant to CIL. Furthermore, the law of treaties came into existence pursuant to CIL, although this law is today codified in treaty. But moving beyond these foundational areas, CIL addresses, for example, issues of territorial integrity, jurisdiction to apply law, diplomatic immunity, the rights of states with respect to coastal areas, human rights, cross-border pollution and the use of force to settle international disputes. These are diverse fields, each with its own characteristics. Our theoretical approach calls for discrimination among these fields. The parameters for discrimination are indicated by the model set forth below. Simply put, we would expect greater possibility for formation of and compliance with CIL in some fields than in others. Of course, this is an area in which empiricism would require analysis of areas in which CIL has not developed: the dog that did not bark. Thus, we might ask, why is there no CIL rule that prohibits over-fishing in international waters? Why is there no CIL rule that requires extradition of criminals? Our theoretical approach also accepts the possibility of linkage among diverse fields, integrating and therefore homogenizing the behavioral effect of each rule of law. b. Four Literatures 7 Goldsmith & Posner 1999, supra note 2. 8 Maurice H. Mendelson, The Formation of Customary International Law, 272 RECUEIL DES COURS 155, 268-293 (1998)
The Customary International Law Supergame February 23, 2004 This article draws on four semi-autonomous literatures. First, as noted above there is an emerging rationalist, law and economics-based literature of CIL. The leading work in this area is by goldsmith and Posner, but there are other important contributions Second, this article draws on a burgeoning literature on social norms in the law, although social norms are studied by all manner of social scientists. Third, this article draws from he economics field of industrial organization analogies to game theory-based insights about collusion among competitors in markets. Fourth, this article draws from the political science literature of international organization, which has addressed in detail the game theoretic analysis of cooperation among groups of states. Law and economics of cil Goldsmith and Posner provide a game theoretic analysis of CIL. They examine a variety of CIL circumstances, and argue that they can be categorized into four game types: (1)coincidence of interest, (ii) coercion, (iii) bilateral cooperation, and (iv coordination. This is a useful exercise. as it invites us to consider the motivation of states, and the degree to which Cil affects behavior. In the perhaps hypothetical cases of pure coincidence of interest and coercion, Goldsmith and Posner are correct that there can be no opinio juris, and that law does little work. This is not new to Cil doctrine, but it is useful to emphasize. It is also useful to emphasize that Goldsmith and Posner seem to assume a purity of motivation that may not exist in the real world Goldsmith and Posner suggest that many instances of observed CIL may be understood in terms of bilateral cooperation along the lines of a bilateral prisoner's dilemma game. They then argue that"Although game theory does not rule out the possibility of n-state cooperation, the assumptions required for such an outcome are quite strong and usually unrealistic. For this reason, we doubt the utility of n-player prisoner's dilemmas as an explanation for multilateral or universal behavioral regularities. Their views with respect to coordination games are similar. In addition to developing this theoretical perspective, Goldsmith and Posner examine several examples of CIL. The areas they consider are neutrality, diplomatic immunity and maritime jurisdiction. They find that in these areas, states were motivated by coincidence of interest, coercion or a bilateral reciprocity along the lines of the prisoners dilemma. They conclude that if state behavior can be explained by coincidence of interest or coercion, or any other self-interested-motivation, then neither opinio juris nor Cil does any motivational work Social norms We might ask, however, whether the cil problem is different in structure from the social norms context and whether if social norms can affect behavior CIL can as Goldsmith Posner 1999, supra note 2, at 1130
The Customary International Law Supergame February 23, 2004 5 This article draws on four semi-autonomous literatures. First, as noted above, there is an emerging rationalist, law and economics-based literature of CIL. The leading work in this area is by Goldsmith and Posner, but there are other important contributions. Second, this article draws on a burgeoning literature on social norms in the law, although social norms are studied by all manner of social scientists. Third, this article draws from the economics field of industrial organization analogies to game theory-based insights about collusion among competitors in markets. Fourth, this article draws from the political science literature of international organization, which has addressed in detail the game theoretic analysis of cooperation among groups of states. i. Law and Economics of CIL Goldsmith and Posner provide a game theoretic analysis of CIL. They examine a variety of CIL circumstances, and argue that they can be categorized into four game types: (i) coincidence of interest, (ii) coercion, (iii) bilateral cooperation, and (iv) coordination. This is a useful exercise, as it invites us to consider the motivation of states, and the degree to which CIL affects behavior. In the perhaps hypothetical cases of pure coincidence of interest and coercion, Goldsmith and Posner are correct that there can be no opinio juris, and that law does little work. This is not new to CIL doctrine, but it is useful to emphasize. It is also useful to emphasize that Goldsmith and Posner seem to assume a purity of motivation that may not exist in the real world. Goldsmith and Posner suggest that many instances of observed CIL may be understood in terms of bilateral cooperation along the lines of a bilateral prisoner’s dilemma game. They then argue that “Although game theory does not rule out the possibility of n-state cooperation, the assumptions required for such an outcome are quite strong and usually unrealistic. For this reason, we doubt the utility of n-player prisoner's dilemmas as an explanation for multilateral or ‘universal’ behavioral regularities.” 9 Their views with respect to coordination games are similar. In addition to developing this theoretical perspective, Goldsmith and Posner examine several examples of CIL. The areas they consider are neutrality, diplomatic immunity and maritime jurisdiction. They find that in these areas, states were motivated by coincidence of interest, coercion or a bilateral reciprocity along the lines of the prisoner’s dilemma. They conclude that if state behavior can be explained by coincidence of interest or coercion, or any other self-interested-motivation, then neither opinio juris nor CIL does any motivational work. ii. Social Norms We might ask, however, whether the CIL problem is different in structure from the social norms context, and whether if social norms can affect behavior, CIL can as 9 Goldsmith & Posner 1999, supra note 2, at 1130
The Customary International Law Supergame February 23, 200 well. Since the publication by Robert Ellickson of Order Without Law in 1991, legal scholars have examined the role of informal norms in society, and the relationship of these norms to law. Ellickson investigates how cattle farmers in Shasta County California, manage to establish and apply their own non-legal rules, with a notable level of compliance, without direct intervention by the state. It is an insightful story about how order can arise without law, or in spite of law We may draw a rough, and limited, analogy between the development of social norms in a municipal, or private setting, and the development of CIl in the international public setting. In the international community, CiL is substantively similar to the phenomenon Ellickson describes. In international political science, regime theorists uch as robert Keohane, Stephen Krasner, and Beth Simmons have told a similar story of the possible rise of order in international society. However, regime theory has generally avoided cIL. Moreover, recognition that a rule has become part of CIl may signal its support by, or linkage with, the multi-Sector CIL system. This system of accepted and enforced linkage may distinguish legal rules from non-legal regimes he difference between law and social norms in the municipal setting is that law is the province of the state(setting aside for the moment religious law, other non-state rules, and circumstances in which non-state made rules are incorporated in the state- enforced law). However, this distinction is inapposite to the international system, which has been characterized as a horizontal, as opposed to vertical, system, where there ROBERT ELLICKSON, ORDER WITHOUT LAW(1991) I However, one might argue that the general legal system, including especially its rules against violence, forms an important background or infrastructure that may provide upport to the farmers' social norms For a recent work synthesizing and extending some of the social norms learning, see ERIC A POSNER, LAW AND SOCIAL NORMS(2000). See also richard H. McAdams, Book Review: Signaling Discount Rates: Law, Norms and Economic Methodology, 110 YALE LJ.625(2001). For an example of this type of analogical allegory, comparing domestic custom to international custom, see Mendelson, supra note 8, at 165-168. For an early statement that CiL is produced in an evolutionary fashion, see ANTHONY A D'AMATO, THE CONCEPT OF CUSTOM IN INTERNATIONAL LAW 104(Cornell 1971) See, e.g., ROBERT O. KEOHANE, AFTER HEGEMONY: COOPERATION AND DISCORDIN THE WORLD POLITICAL ECONOMY(1984); ROBERT O KEOHANE, INTERNATIONAL INSTITUTIONS AND STATE POWER: ESSAY IN INTERNATIONAL RELATIONS THEORY(1989) See, e.g, STEPHEN D. KRASNER, INTERNATIONAL REGIMES (1983); Stephen Krasner Beth Simmons, Theories of International Regimes, 41 INT'L ORG. 491(1987) 16 Duncan Nidal, Political Economy and International InstitutionS, 16 INT'L REV. L.& ECON.121,124(1996) ile there is no state at the global level, there is an international legal and organizational order, which is quite a bit more fragmented than most nation-states
The Customary International Law Supergame February 23, 2004 6 well. Since the publication by Robert Ellickson of Order Without Law 10 in 1991, legal scholars have examined the role of informal norms in society, and the relationship of these norms to law. Ellickson investigates how cattle farmers in Shasta County, California, manage to establish and apply their own non-legal rules, with a notable level of compliance, without direct intervention by the state. It is an insightful story about how order can arise without law, or in spite of law. 11 We may draw a rough, and limited, analogy between the development of social norms in a municipal, or private setting, 12 and the development of CIL in the international public setting. In the international community, CIL is substantively similar to the phenomenon Ellickson describes. 13 In international political science, regime theorists such as Robert Keohane, 14 Stephen Krasner, and Beth Simmons 15 have told a similar story of the possible rise of order in international society. However, regime theory has generally avoided CIL. 16 Moreover, recognition that a rule has become part of CIL may signal its support by, or linkage with, the multi-sector CIL system. This system of accepted and enforced linkage may distinguish legal rules from non-legal regimes. The difference between law and social norms in the municipal setting is that law is the province of the state (setting aside for the moment religious law, other non-state rules, and circumstances in which non-state made rules are incorporated in the stateenforced law). 17 However, this distinction is inapposite to the international system, which has been characterized as a horizontal, as opposed to vertical, system, where there 10 ROBERT ELLICKSON, ORDER WITHOUT LAW (1991). 11 However, one might argue that the general legal system, including especially its rules against violence, forms an important background or infrastructure that may provide support to the farmers' social norms. 12 For a recent work synthesizing and extending some of the social norms learning, see ERIC A. POSNER, LAW AND SOCIAL NORMS (2000). See also Richard H. McAdams, Book Review: Signaling Discount Rates: Law, Norms and Economic Methodology, 110 YALE L.J. 625 (2001). 13 For an example of this type of analogical allegory, comparing domestic custom to international custom, see Mendelson, supra note 8, at 165-168. For an early statement that CIL is produced in an evolutionary fashion, see ANTHONY A. D'AMATO, THE CONCEPT OF CUSTOM IN INTERNATIONAL LAW 104 (Cornell 1971). 14 See, e.g., ROBERT O. KEOHANE, AFTER HEGEMONY: COOPERATION AND DISCORD IN THE WORLD POLITICAL ECONOMY (1984); ROBERT O. KEOHANE, INTERNATIONAL INSTITUTIONS AND STATE POWER: ESSAY IN INTERNATIONAL RELATIONS THEORY (1989). 15 See, e.g., STEPHEN D. KRASNER, INTERNATIONAL REGIMES (1983); Stephen D. Krasner & Beth Simmons, Theories of International Regimes, 41 INT’L ORG. 491 (1987). 16 Duncan Snidal, Political Economy and International Institutions, 16 INT'L REV. L. & ECON. 121, 124 (1996). 17 While there is no state at the global level, there is an international legal and organizational order, which is quite a bit more fragmented than most nation-states
The Customary International Law Supergame February 23, 2004 is no overarching state, per se. So, in the international system, there is more overlap, and an indistinct border, between law and social norms. This overlap is perhaps easier to see in the international context than in the domestic context as in the international context, a significant subset of social norms is termed law. Ellickson states that the social norms literature defines a" social norm as"a rule governing an individuals behavior that third parties other than state agents diffusely enforce by means of social sanctions. "l9 The focus of this definition on decentralized means of enforcement shows the strong analogy between social norms in the municipal setting and cil in the international setting. Of course, to the extent that courts may apply, and institutions of global governance may enforce, CIL, there is a difference. But this application and enforceability is quite limited. There are few circumstances in which at the international level although action by domestic courts would certainl ageny s, O consider application of Cil by domestic courts to amount to the action of"stae ould CIL rules benefit from mandatory adjudication in international tribunals. We would not considered action of state agents"at the municipal level. This is because in the nternational context, domestic courts are simply internal deliberative processes of national governments. The application by domestic courts of cil may be understood as a kind of norm internalization. 20 One important set of explanations of social norms understands norms as preferences that individuals(or in our case states) acquire through education acculturation or other processes, such as an expressive or articulation function. Elster states that" social norms provide an important kind of motivation for action that is irreducible to rationality or indeed to any other form of optimizing mechanism We add this qualification, because one might argue that the cil and conventional law framework, as it exists, is at least comparable to a municipal state, or at least that this framework is comparable to the constitution that a municipal state might have. Of course, while it responds to some of the same questions, including a rule of recognition, it is not as detailed or fertile as a constitution Robert Ellickson, The Evolution of social Norms: A Perspective from the legal Academy, in SoCIAL NORMS 35(Michael Hechter Karl-Dieter Opp eds, 2001). Note that Ellickson assumes multilateral, as opposed to bilateral, retaliation 20 See Harold Hongju Koh, Why Do Nations Obey International Law?, 106YALELJ 2599(1997)(reviewing Abram Chayes Antonia Handler Chayes, THE NEW SOVEREIGNTY: COMPLIANCE WITH INTERNATIONAL REGULATORY AGREEMENTS (1995)) This internalization may be desirable under certain circumstances, and may be developed as a tool of enforcement of CIL. That is, states may persuade one another to harness their domestic legal system for certain of their international legal obligations, effectively holding the domestic legal system hostage. See also Philip moremen Joel P Trachtman, Whose Right is it Anyway? Private Parties in EC-US. Dispute Settlement at the WTo, 44 HARV. INT'L L J. 221(2003). See robert d. Cooter, Expressive Law and Economics, 27J LEG. STUDS. 585(1998). JON ELSTER, THE CEMENT OF SOCIETY 15(1989)
The Customary International Law Supergame February 23, 2004 7 is no overarching state, per se. 18 So, in the international system, there is more overlap, and an indistinct border, between law and social norms. This overlap is perhaps easier to see in the international context than in the domestic context, as, in the international context, a significant subset of social norms is termed "law." Ellickson states that the social norms literature defines a “social norm” as “a rule governing an individual’s behavior that third parties other than state agents diffusely enforce by means of social sanctions.” 19 The focus of this definition on decentralized means of enforcement shows the strong analogy between social norms in the municipal setting and CIL in the international setting. Of course, to the extent that courts may apply, and institutions of global governance may enforce, CIL, there is a difference. But this application and enforceability is quite limited. There are few circumstances in which CIL rules benefit from mandatory adjudication in international tribunals. We would not consider application of CIL by domestic courts to amount to the action of “state agents” at the international level, although action by domestic courts would certainly be considered action of “state agents” at the municipal level. This is because in the international context, domestic courts are simply internal deliberative processes of national governments. The application by domestic courts of CIL may be understood as a kind of norm internalization. 20 One important set of explanations of social norms understands norms as preferences that individuals (or in our case states) acquire through education, acculturation or other processes, such as an expressive or articulation function. 21 Elster states that “social norms provide an important kind of motivation for action that is irreducible to rationality or indeed to any other form of optimizing mechanism . . . .” 22 It 18 We add this qualification, because one might argue that the CIL and conventional law framework, as it exists, is at least comparable to a municipal state, or at least that this framework is comparable to the constitution that a municipal state might have. Of course, while it responds to some of the same questions, including a rule of recognition, it is not as detailed or fertile as a constitution. 19 Robert Ellickson, The Evolution of Social Norms: A Perspective from the Legal Academy, in SOCIAL NORMS 35 (Michael Hechter & Karl-Dieter Opp eds., 2001). Note that Ellickson assumes multilateral, as opposed to bilateral, retaliation. 20 See Harold Hongju Koh, Why Do Nations Obey International Law?, 106 YALE L.J. 2599 (1997) (reviewing Abram Chayes & Antonia Handler Chayes, THE NEW SOVEREIGNTY: COMPLIANCE WITH INTERNATIONAL REGULATORY AGREEMENTS (1995)). This internalization may be desirable under certain circumstances, and may be developed as a tool of enforcement of CIL. That is, states may persuade one another to harness their domestic legal system for certain of their international legal obligations, effectively holding the domestic legal system hostage. See also Philip Moremen & Joel P. Trachtman, Whose Right is it Anyway? Private Parties in EC-U.S. Dispute Settlement at the WTO, 44 HARV. INT’L L. J. 221 (2003). 21 See Robert D. Cooter, Expressive Law and Economics, 27 J. LEG. STUDS. 585 (1998). 22 JON ELSTER, THE CEMENT OF SOCIETY 15 (1989)
The Customary International Law Supergame February 23, 2004 may well be possible to modify preferences of states through social norms. It seems individual government officials, or voters. Indeed, it may be appropriate to consider obvious that the way to modify the preferences of states is to modify the preferences epistemic communities and networks among government officials. While this approach may have traction in the CIL setting, and may re-emphasize the role of legitimacy, justice and morality as bases for preference-modification, this article will bypass that di scussion and focus on exogenous explanations of social norms. Modeling always involves plification, and our goal in this paper is to elaborate a rationalist model for future testing. In fact, testing a rationalist model would help to clarify the debate between exogenous preferences and endogenous preferences In connection with exogenous explanations, the law-based social norms literature has not embraced the iterated n-person prisoners dilemma. This is due to two types of concerns. First, there are concerns that game theory does not reflect the nuance of social interaction. We hope that the incorporation in our model of multi-issue contact helps to address this concern. Second, there are concerns about individual rationality: the subgame perfection of third-party enforcement. We address these concerns below iii. Industrial organization Much of our understanding of the utility, structure and dynamics of n-player prisoner's dilemma games comes from the economics literature of industrial organization. This literature considers the possibility that firms may enter into cartels or other restrictions of competition that violate antitrust laws. While firms may find opportunities to communicate, their communications and agreements must be kept secret from the regulatory authorities and are not enforceable at law. An important concern for industrial organization economists is to identify circumstances under which such agreements can be made self-sustaining through the self-interest of the parties to the agreement Robert D. Cooter, Do Good Laws Make Good Citizens? An Economic Analysis of Internalized Norms, 86 VA L REV. 1577(2000); Robert C. Cooter, Models of morali in Law and Economics: Self-Control and Self-Improvement for the"Bad Man"of Holmes, 78B U L REV. 903, 911-912(1998): JON ELSTER, THE CEMENT OF SOCIETY: A STUDY OF SOCIAL ORDER (1989). Basu refers to these as "preference-changing norms See Kaushik basu. Social norms and the law. 3 THE NEW PALGRAVE DICTIONARY OF ECONOMICS AND THE LAW 476(1998) See Paul g. Mahoney Chris William Sanchirico, Norms, Repeated Games, and the Role of law, 91 CAL L REV. 1281, 1284(2003). Mahoney and Sanchirico explain the state of the social norms literature with respect to the n-person prisoners dilemma. They explain that the objection to these models is that third party enforcement is not individually rational: that the incentives of the players break down. ld at note 12, citing work by Ellickson, Katz, McAdams and Posner
The Customary International Law Supergame February 23, 2004 8 may well be possible to modify preferences of states through social norms. It seems obvious that the way to modify the preferences of states is to modify the preferences of individual government officials, or voters. Indeed, it may be appropriate to consider epistemic communities and networks among government officials. While this approach may have traction in the CIL setting, and may re-emphasize the role of legitimacy, justice and morality as bases for preference-modification, this article will bypass that discussion, and focus on exogenous explanations of social norms. 23 Modeling always involves simplification, and our goal in this paper is to elaborate a rationalist model for future testing. In fact, testing a rationalist model would help to clarify the debate between exogenous preferences and endogenous preferences. In connection with exogenous explanations, the law-based social norms literature has not embraced the iterated n-person prisoner’s dilemma. 24 This is due to two types of concerns. First, there are concerns that game theory does not reflect the nuance of social interaction. We hope that the incorporation in our model of multi-issue contact helps to address this concern. Second, there are concerns about individual rationality: the subgame perfection of third-party enforcement. 25 We address these concerns below. iii. Industrial Organization Much of our understanding of the utility, structure and dynamics of n-player prisoner’s dilemma games comes from the economics literature of industrial organization. This literature considers the possibility that firms may enter into cartels or other restrictions of competition that violate antitrust laws. While firms may find opportunities to communicate, their communications and agreements must be kept secret from the regulatory authorities and are not enforceable at law. An important concern for industrial organization economists is to identify circumstances under which such agreements can be made self-sustaining through the self-interest of the parties to the agreement. 23 Robert D. Cooter, Do Good Laws Make Good Citizens? An Economic Analysis of Internalized Norms, 86 VA. L. REV. 1577 (2000); Robert C. Cooter, Models of Morality in Law and Economics: Self-Control and Self-Improvement for the “Bad Man” of Holmes, 78 B.U. L. REV. 903, 911-912 (1998); JON ELSTER, THE CEMENT OF SOCIETY: A STUDY OF SOCIAL ORDER (1989). Basu refers to these as “preference-changing norms.” See Kaushik Basu, Social Norms and the Law, 3 THE NEW PALGRAVE DICTIONARY OF ECONOMICS AND THE LAW 476 (1998). 24 See Paul G. Mahoney & Chris William Sanchirico, Norms, Repeated Games, and the Role of Law, 91 CAL. L. REV. 1281, 1284 (2003). Mahoney and Sanchirico explain the state of the social norms literature with respect to the n-person prisoner’s dilemma. They explain that the objection to these models is that third party enforcement is not individually rational: that the incentives of the players break down. 25 Id. at note 12, citing work by Ellickson, Katz, McAdams and Posner
The Customary International Law Supergame February 23, 200 While the analogy is apparent, we must recognize, of course, that in the cil setting, public communication is possible, as are agreements that at least purport to be binding: treaties. The degree to which agreements may actually constrain behavior is a question for another paper, but we point out that the international legal rule that treatio must be observed (pacta sunt servanda) is itself part of CiL Another, perhaps more important, distinction is that a cartel has certain haracteristics that may differ from any particular CIL setting. That is, in a cartel, the more others adhere to the cartel, the greater the monetary incentives for any particular member to defect. This context is more like a commons problem than like a public good problem. We will discuss some of these distinctions based on payoff structures below iv. International Organization Political scientists and economists working in the field of international organization have made a good deal of progress in anal yzing the problem of international cooperation more generally. In various works, they have examined most of th parameters that we utilize here. This literature has not examined CIL We have structured our model to match most closely the Cil context, rather than attempt to structure a model that would address other international cooperation devices However, we recognize that the question of which device-treaty, CiL or softer law- itself depends on a set of variables. We also recognize that Cil may be understood as a phase in the formalization of law, or in"legalization. CIL is often codified by the nternational law Commission of the united nations and cil often forms the basis for treaty, or of the relationship among these instruments. 28 oi treaties. This article does not present an explanation of choice between custom and There is disagreement between institutionalists and"realists, who claim that states' interests in international relations are characterized by a search for relative gains, rather than absolute gains. These realists reject the possibility of cooperation where it results in relative gains to a competitor. See marc Busch Eric Reinhardt, Nice Strategies in a World of relative Gains: The Problem of Cooperation under Anarchy 37 J CONFL RES 427(1993); Robert Powell, Absolute and Relative Gains in international relations Theory, 85 AM. POL. SCI. REV. 1303(1991); Duncan Snidal, Relative Gains and the Pattern of International Cooperation, 85 AM. POL. SCL. REV. 701(1991) See the special issue of International Organization devoted to the phenomenon of legalization. 54: 3 INT'L ORG. (2000) See Kenneth Abbott Duncan Nidal, Hard and Soft law in International Governance, 54 INT'L ORG. (2000); John K. Setear, Treaty, Custom, Iteration and public Choice,February2004,availableathttpssrn.com/abstract=492604(arguingthatcustom is more attractive to executive branches ). To the extent that cil is less detailed-less specific-than treaty norms, it is amenable to a rules versus standards type of analysis See louis Kaplow, Rules versus Standards: An Economic Analysis, 42 DUKE L.J. 557
The Customary International Law Supergame February 23, 2004 9 While the analogy is apparent, we must recognize, of course, that in the CIL setting, public communication is possible, as are agreements that at least purport to be binding: treaties. The degree to which agreements may actually constrain behavior is a question for another paper, but we point out that the international legal rule that treaties must be observed (pacta sunt servanda) is itself part of CIL. Another, perhaps more important, distinction is that a cartel has certain characteristics that may differ from any particular CIL setting. That is, in a cartel, the more others adhere to the cartel, the greater the monetary incentives for any particular member to defect. This context is more like a commons problem than like a public good problem. We will discuss some of these distinctions based on payoff structures below. iv. International Organization Political scientists and economists working in the field of international organization have made a good deal of progress in analyzing the problem of international cooperation more generally. In various works, they have examined most of the parameters that we utilize here. 26 This literature has not examined CIL. We have structured our model to match most closely the CIL context, rather than attempt to structure a model that would address other international cooperation devices. However, we recognize that the question of which device—treaty, CIL or softer law— itself depends on a set of variables. We also recognize that CIL may be understood as a phase in the formalization of law, or in “legalization.” 27 CIL is often codified by the International Law Commission of the United Nations, and CIL often forms the basis for treaties. This article does not present an explanation of choice between custom and treaty, or of the relationship among these instruments. 28 26 There is disagreement between institutionalists and “realists,” who claim that states’ interests in international relations are characterized by a search for relative gains, rather than absolute gains. These realists reject the possibility of cooperation where it results in relative gains to a competitor. See Marc Busch & Eric Reinhardt, Nice Strategies in a World of Relative Gains: The Problem of Cooperation under Anarchy 37 J. CONFL. RES. 427 (1993); Robert Powell, Absolute and Relative Gains in International Relations Theory, 85 AM. POL. SCI. REV. 1303 (1991); Duncan Snidal, Relative Gains and the Pattern of International Cooperation, 85 AM. POL. SCI. REV. 701 (1991). 27 See the special issue of International Organization devoted to the phenomenon of “legalization.” 54:3 INT’L ORG. (2000). 28 See Kenneth Abbott & Duncan Snidal, Hard and Soft Law in International Governance, 54 INT’L ORG. (2000); John K. Setear, Treaty, Custom, Iteration and Public Choice, February 2004, available at http://ssrn.com/abstract=492604 (arguing that custom is more attractive to executive branches). To the extent that CIL is less detailed—less specific—than treaty norms, it is amenable to a rules versus standards type of analysis. See Louis Kaplow, Rules versus Standards: An Economic Analysis, 42 DUKE L.J. 557
