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)