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)