How to select and develop international law case studies: lessons from comparative law and comparative politics.

Author:Linos, Katerina
Position:Comparative International Law: Framing the Field

    To develop international law claims, it is often critical to compare different countries' laws. This essay explores how methods drawn from comparative law and comparative politics research can help international lawyers make comparative inquiries more simply and straightforwardly.

    International lawyers recognize three main sources of legal authority: treaties, custom, and general principles. (1) Cross-national comparisons are deeply embedded in the very definitions of two of these three sources. To establish international custom, an international lawyer must show that a broad range of states consistently engage in a certain practice out of a sense of legal obligation. To establish a general principle, an international lawyer must show that it is "recognized by civilized nations"; in practice this requires that the principle be found in diverse legal families. Treaty interpretation does not necessitate cross-country comparison as a matter of definition: in theory, the text of the treaty itself could provide the requisite answers. However, in practice, international and domestic courts are typically faced with ambiguous treaty terms. To interpret them, they often turn to the jurisprudence of diverse states and to subsequent state practice, (2) thus implicitly beginning a comparative inquiry. In sum, comparative international law is useful for identifying and applying international law, as this volume's introduction explains.

    But international law scholars often take on additional tasks: not only do we seek to establish what international law is as a matter of current doctrine, but we also try to assess how it operates in practice and what directions it should take in the future. Cross-national comparisons are also critical in performing these tasks, and are needed both to evaluate important enforcement and implementation challenges and to design reform alternatives. After all, international rules and institutions are intended to govern conduct in many countries that face diverse challenges.

    Traditional legal training provides important rules on how to choose and analyze cases. But these traditional rules aim to focus lawyers' attention on cases and propositions that have a high degree of legal authority within a domestic legal system. These traditional rules can be less helpful, even misleading, to international lawyers seeking to make either doctrinal claims involving cross-country generalizations or causal inferences about how law interacts with economic and social forces. For example, traditional legal training prompts a lawyer to ask whether the case comes from a lower court or a higher court. The higher the court, the greater the domestic authority it has, and thus the more relevant the case is likely to be to the development of a doctrinal argument within the particular jurisdiction. However, while cases from higher courts are more authoritative legally than cases from lower courts, they are also subject to much stronger selection biases, as a long tradition of scholars have argued. (3) That is, because only a subset of parties have the willingness, the resources, and, sometimes, the legal right or court permission to appeal a case after having lost, it is likely that cases before high courts are atypical. Cases before higher courts are more likely to involve novel issues, issues over which there is significant uncertainty, and at least one well-resourced party. If a principle of law is well established in a country, it is likely to be rarely litigated and, when litigated, unlikely to be appealed all the way to the country's highest court. International lawyers seeking to establish international custom or general principles of law are often looking for such well-established principles. So a first idea might be to look beyond the case law of a country's highest court to locate such well-established rules.

    Traditional legal training also leads us to ask which jurisdiction the case comes from. But while lawyers know that cases from one's home jurisdiction are likely to have greater authority than cases from other jurisdictions before domestic courts, we often receive little training in how to select among foreign cases. To conduct cross-country comparisons, international lawyers usually turn to a handful of familiar jurisdictions. In a recent study of international law casebooks and textbooks from around the world, Anthea Roberts highlights that citations to foreign cases in very different countries, including casebooks and textbooks from Australia and South Africa, as well as France and China, focus overwhelmingly on two English-speaking jurisdictions: the United States and the United Kingdom. (4) Cases from other rich Western courts, notably France, Israel, and Canada, also elicited a good number of citations, but citations to cases from outside the West were extremely rare. (5) There are certainly plausible sociological explanations for these patterns, such as the importance of case law in the common law tradition, and the centrality of the United States and the United Kingdom in the legal training of academics from around the world. However, these citation patterns are at odds with international law principles that call for surveys of a broad range of countries--not comparisons of a handful of similarly situated states. The tendency to cite predominantly to a handful of rich Western democracies is not limited to the authors of international law casebooks and textbooks: both domestic U.S. courts (6) and even European regional courts (7) show similar, though somewhat less pronounced, biases.

    This mismatch between international law rules and social science methodologies that require systematic cross-country comparisons and the actual citation patterns of international law texts, domestic courts, and even international courts is cause for consternation. To date, international lawyers have proposed two types of solutions. The first type of solution involves changing fundamental international law rules to simplify the comparative exercise. For example, the International Law Association's Committee on Formation of Customary International Law has proposed that the very definition of custom be changed, so that lawyers will only have to establish one fact, rather than two, about any jurisdiction. This proposal suggests that we should redefine custom by studying state practice alone, rather than also having to document opinio juris--states' subjective beliefs that particular practices are required by law. (8) The second type of approach--which I call the brute force approach--involves adding more country cases and moving from the United States and the United Kingdom to ten, twenty, or even thirty or forty examples. This second approach is time-consuming and often unconvincing as there is no guarantee that additional cases that are unsystematically selected will allow us to confirm or disconfirm important principles.

    Where should authors, courts, and researchers start their comparisons? How can they know whether they are cherry-picking examples that favor their preferred conclusions? When is it best to develop examples from countries that are very different from one's own, and when should one focus on countries that are very similar? Which aspects of foreign systems are most relevant for particular inquiries? The fields of comparative law and comparative politics have made tremendous progress on each of these questions. This essay synthesizes their key findings, and applies them to fundamental questions in international law. The goal of this essay is to briefly present ideas that are very well developed in other fields, and to illustrate why they might prove useful to the development of international law claims. The interested reader can then turn to the cited works for a more extensive treatment of techniques that seem potentially useful.


    Establishing that a practice is commonplace among diverse legal systems is critical to the development of claims about international custom and general principles of law. It can also be very helpful for the purpose of treaty interpretation and the development of claims linking international law doctrine to diverse domestic societies. Sometimes, relevant evidence on the entire universe of cases--approximately 200 sovereign states--is available. For example, international...

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