International law in national legal systems: an empirical investigation.

Author:Verdier, Pierre-Hugues
Position:Comparative International Law: Framing the Field

    International legal scholars have long recognized the importance of the rules and processes by which states adhere to international legal obligations and "translate" them into their domestic legal systems. (1) Research by political scientists on specific issue areas likewise increasingly recognizes that domestic implementation is crucial to international law compliance and effectiveness. (2) Yet the lack of systematic data makes it difficult to assemble an overall picture of the relationship between international law and domestic law around the world, let alone to document its evolution over time. Recent qualitative surveys of state practice have begun to fill that gap, but provide only a snapshot in time and are limited to relatively few countries. (3) Some quantitative projects cover more countries, but address only a limited number of questions based solely on the text of national constitutions. (4)

    In this essay, we draw upon a new dataset arising from a multi-year research project on international law in domestic legal systems. This dataset provides what we believe is uniquely systematic and comprehensive information on the relationship between international and national legal orders. The dataset captures numerous specific features of approaches in national legal systems to international law, including treaty-making procedures, the status of treaties in domestic law, and the reception of customary international law (CIL). It currently covers 101 countries for the period 1815-2013, thus expanding the scope of inquiry beyond well-known Western states to include numerous states in Africa, Asia, Latin America, and the former Soviet Union. It covers a longer period than existing data, thus allowing identification and analysis of historical trends. It incorporates information found not only in constitutions but also in statutes, case law, executive and administrative documents, and secondary sources. This data allows us to move beyond traditional monist-dualist classifications and provide a more nuanced exploration of how countries address international law in their domestic legal systems.

    In the following sections, we describe salient features of the data, identify major trends in national approaches to international law, and discuss their implications for comparative international law. We find that, in aggregate, national approaches to treaty making and implementation have changed considerably, and we suggest that the direction of change reflects simultaneous concern with securing effective implementation of a growing body of treaty law and addressing greater accountability and legitimacy concerns as more governance functions migrate to the international level. More specifically, we find that national legal systems have become more likely to give treaties direct effect and hierarchical superiority over domestic law, which is consistent with a desire to ensure effective implementation. At the same time, national legal systems have steadily expanded the categories of treaties whose ratification requires prior legislative approval, thus expanding the role of national legislatures in international lawmaking.

    With respect to CIL, we find remarkable consistency across countries: the vast majority of national legal systems now recognize custom as directly applicable, at least in principle. At the same time, a growing portion of countries consider custom to be hierarchically inferior to domestic law, which limits the ability of courts to apply it directly in many circumstances and preserves the legislature's ability to displace customary rules. Thus, the reception regime for custom reflects both traditional ideas of automatic reception of the law of nations in the domestic legal order and contemporary suspicion of the custom formation process, including its lack of formal consent by domestic political institutions.

    These trends in domestic legal orders' attitudes towards treaties and international custom hold important insights for comparative international law. For instance, our data provides information on the respective roles of such domestic political institutions as executives, legislatures, and courts in engaging with international law, which can inform comparative analysis. Although we propose conjectures about how the trends we identify relate to broader phenomena--such as the changing nature of the international legal order and debates over the democratic deficit--the methods we use do not allow us to make any causal claims. Our sample of countries is too diverse and the number of confounding variables is too large for such claims to be made and substantiated within the framework of this essay. Our primary purpose here is to document global patterns and trends and to propose hypotheses as to their potential causes and relationships that may be tested by future comparative international law scholarship.


    Differences between countries in the relationship between international law and domestic legal systems are often accounted for in international law textbooks by reference to the monistdualist distinction. According to this distinction, monist systems regard international law and national law as "two parts of a single system" in which "international law automatically passes into the state's legal system," so that "when the state ratifies a treaty, that treaty is automatically and fully incorporated into national law." (5) Indeed, in a "pure" monist system, "national law is seen as ultimately deriving its authority from international law, which stands higher in the hierarchy of legal norms." (6) By contrast, dualist systems regard international law and national law as "separate legal systems" wherein "[a] rule of international law binding upon the state does not automatically become a part of national law; it only does so when it has been transformed or incorporated into national law by an act at the national level, such as an implementing statute for a treaty." (7)

    As our study makes clear, the monist-dualist distinction has fundamental limitations for the purpose of classifying national approaches to international law. First, because they derive from a theoretical debate about the nature of international law rather than an effort to classify actual legal systems, "neither theory offers an adequate account of the practice of international and national courts, whose role in articulating the positions of the various legal systems is crucial." (8) Second, national systems do not adopt a monolithic approach to international law; most of them combine aspects of the monist and dualist approaches. For example, in the United Kingdom treaties do not become part of domestic law unless implemented by Parliament, while courts may directly apply international custom. Finally, because the distinction is articulated at a high level of generality, scholars sometimes differ as to whether a particular country should properly be classified as "monist" or "dualist." For example, while many observers consider France to be a monist country, some leading French scholars maintain that, because the direct effect and superiority of treaties in France does not rest on their international validity but on the French constitution, the country is really "dualist." (9)

    For these reasons, in assembling our dataset, we go beyond the monist-dualist distinction to provide a more detailed picture of state practice. In doing so, we also go substantially beyond existing research. Unlike existing qualitative surveys, (10) our dataset covers a broad range of countries from all regions of the world, systematically addresses a standard set of questions, and codes the answers in quantitative form to permit visual display and statistical analysis. Instead of providing a snapshot in time, our dataset covers the period 1815-2013, providing the first systematic picture of the evolution of national approaches to international law during that period. Another defining feature of our dataset is that it relies not only on national constitutions, but also on information found in ordinary legislation, case law, executive and administrative documents, and secondary sources. We follow this approach because constitutions usually only partially define a state's relationship with international law and, in some cases, are silent on the matter altogether. In that sense, our data differs from existing initiatives by Hathaway (11) and the Comparative Constitutions Project, (12) which assemble information on the domestic status of international law based on constitutions alone.

    In collecting our data, a first step was to identify and define the substantive issues that define a state's relationship with international law. We identified about fifty issues under the categories of treaty making, treaty reception, and CIL reception. For each country, we commissioned a written memorandum that provides a narrative answer to each of the questions and, where applicable, documents how this answer has changed over time. (13) These memorandums were written by the principal investigators or by scholars, professors, and students that usually possessed substantial knowledge on the foreign legal system in question. Where multiple interpretations existed, we relied on the most authoritative source of that system to make a judgment call. The principal investigators conducted all of the coding.

    Because our goal is to provide a comprehensive picture of international law in national legal systems, we include a wide range of countries: rich and poor, Western and non-Western, democratic and non-democratic. At first blush, this choice may raise questions as to the significance of the rules and procedures we identify across different regime types. For example, one might doubt that non-democratic states would require prior legislative approval of treaty ratification, and that if such provisions exist, they...

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