CHICAGO WORKING PAPER IN LAW AND ECONOMICS by concession, is insufficient by itself to establish CIL. To avoid this problem, courts and scholars sometimes(but only sometimes independent evidence that a nation acted from a sense obligation, such as a statement by an important government official ratification of a treaty that contains a norm similar to the cil norm in question, or an attitude of approval toward a General Assembly Resolution. 20 The appropriate conditions on the use of such evidence remains unsettled, and indeed the evidence is never considered in a systematic fashion These definitional problems with opinio juris flow in part from more serious conceptual difficulties. There is no convincing explanation of the process by which a voluntary behavioral regularity transforms itself into a binding legal obligation. 21 Opinio juris is described as the psychological component of cil because it refers to an attitude that nations supposedly have toward a behavioral regularity. The idea is mysterious because the legal obligation is created by a nation's belief in the existence of the legal obligation. As D'Amato notes, this is circular reasoning. 22 Opinio juris is really a conclusion about a practice's status as international law; it does not explain how a widespread and uniform practice becomes law We have described some of the many uncertainties that bedevil the standard conception of CIL. These problems are well known They are the subject of an enormous literature that endlessly(and in our opinion unproductively) debates definitional issues, the relative significance of practice and opinio juris and other conceptual matters internal to the traditional account. 23 Although our theory has implications for many of these issues, such issues are not the main focus of our analysis. Instead, we focus on two sets of issues that are 20 Id at 7-9(citing examples) 21 For a catalogue of failed attempts, see D'Amato, supra note_,at,66- 22 D'amato captures this circularity with a question: "How can custom create law if its psychological component requires action in conscious accordance with law preexisting the action"? D'Amato, supra note 66. He analyzes the many futile attempts to avoid this paradox, id at 47-56, 66-68 23 The canonical treatments of CIL include D'Amato, supra note supra note Thirlway note: and Michael Akehurst. Custom Source of International Law, 47 Brit. Y B. Int'l L. 1(1974-1975CHICAGO WORKING PAPER IN LAW AND ECONOMICS 8 by concession, is insufficient by itself to establish CIL. To avoid this problem, courts and scholars sometimes (but only sometimes) require independent evidence that a nation acted from a sense of obligation, such as a statement by an important government official, ratification of a treaty that contains a norm similar to the CIL norm in question, or an attitude of approval toward a General Assembly Resolution.20 The appropriate conditions on the use of such evidence remains unsettled, and indeed the evidence is never considered in a systematic fashion. These definitional problems with opinio juris flow in part from more serious conceptual difficulties. There is no convincing explanation of the process by which a voluntary behavioral regularity transforms itself into a binding legal obligation.21 Opinio juris is described as the psychological component of CIL because it refers to an attitude that nations supposedly have toward a behavioral regularity. The idea is mysterious because the legal obligation is created by a nation’s belief in the existence of the legal obligation. As D’Amato notes, this is circular reasoning.22 Opinio juris is really a conclusion about a practice’s status as international law; it does not explain how a widespread and uniform practice becomes law. We have described some of the many uncertainties that bedevil the standard conception of CIL. These problems are well known. They are the subject of an enormous literature that endlessly (and in our opinion unproductively) debates definitional issues, the relative significance of practice and opinio juris, and other conceptual matters internal to the traditional account.23 Although our theory has implications for many of these issues, such issues are not the main focus of our analysis. Instead, we focus on two sets of issues that are 20 Id. at 7-9 (citing examples). 21 For a catalogue of failed attempts, see D’Amato, supra note __, at 47-56, 66- 72. 22 D’amato captures this circularity with a question: “How can custom create law if its psychological component requires action in conscious accordance with law preexisting the action”? D’Amato, supra note __, at 66. He analyzes the many futile attempts to avoid this paradox, id. at 47-56, 66-68. 23 The canonical treatments of CIL include D’Amato, supra note __; Wolfke, supra note __; Thirlway, supra note __; and Michael Akehurst, Custom as a Source of International Law, 47 Brit. Y.B. Int’l L. 1 (1974-1975)