Constitutional Convergence and Customary International Law

In Getting to Rights: Treaty Ratification, Constitutional Convergence, and Human Rights Practice, Zachary Elkins, Tom Ginsburg, and Beth Simmons study the effects of post-World War II human rights texts on domestic constitutions, with a particular focus on the Universal Declaration of Human Rights and the International Covenant on Civil and Political Rights (ICCPR). After analyzing 680 constitutional systems compiled by the Comparative Constitutions Project to create a list of seventy-four constitutionally protected rights, the authors evaluate whether countries incorporate internationally codified human rights into their domestic constitutions, whether ratification of international agreements affects the probability of rights incorporation, and whether such incorporation increases the likelihood that countries enforce rights in practice.

After tabulating the data and running random-effects models, the authors find “a significant upward shift in the similarity to the [Universal Declaration] among constitutions written after 1948,” leading them to conclude that the Universal Declaration acted as a “template” from which constitutional drafters could select rights. They also demonstrate—after controlling for the era and a state’s prior constitutional tradition—that post-1966 constitutions from states that ratified the ICCPR are more likely to include its codified rights in subsequent constitutions than non-ratifying states. Finally, relying on Freedom House’s civil liberties index, the authors conclude that human rights agreement ratification and constitutional incorporation is correlated with improved human rights practice on the ground.

This ambitious project and its quantitative and qualitative findings are applicable to a wide range of international law scholarship. Getting to Rights offers new evidence relevant to convergence theory, provides empirical support for speculation on the effects of international agreements on domestic law, and determines that human rights are most effectively enforced when international and domestic law are applied in tandem. It also suggests a methodology for similar future research into the influence of supranational texts—such as the European, Inter-American, or African Conventions on Human Rights—on domestic constitutions.

From this garden of subjects, this response focuses on one offshoot: the consequences of the authors’ data on rights convergence for customary international law theory. After briefly reviewing the definitions of customary international law and jus cogens, I discuss the potential implications of converging constitutionally protected rights. I then examine the authors’ data in light of these hypotheses and conclude that, from this point forward, scholars who argue that certain norms have obtained customary international law or jus cogens status will have to address the Getting to Rights data. Due to the necessary brevity of this response, however, I leave more complete analyses of individual rights to others.

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