Why Do Nations Obey Custom?

50 Pages Posted: 17 May 2023

Date Written: May 8, 2023


Why do nations obey custom? The conventional model of the law of nations or customary international law (CIL) countenances a separation thesis in that CIL is comprised of two discrete elements: state practice (usus) and a legal consciousness (opinio). This Article argues that the separation thesis is attributable to the time-honored philosophical dilemma in comprehending the reality known as Cartesian “mind-body” dualism. As innocuous as it might sound, the dualism-inspired separation thesis tends to generate grave conceptual and practical quandaries, such as the circularity and dogmatic competition between the two constitutive elements, i.e., state practice and legal consciousness. This Article submits that state practice and state mind should not be separated in the first place, and aims to reinstate an ontological unity between the two elements to better ascertain CIL. The holistic and dynamic thesis proposed by this Article focuses not on the static substances comprising CIL, but on the evolving relations among states leading to the development of CIL. In a given legal community (nomos), each CIL rule undergoes a normative life-cycle: rule-formation (externalization), rule-recognition (objectivation) and rule-following (internalization). Under this sociological approach, a particular behavioral pattern among states emerges from a shared belief in its legal reality. Such behavioral regularity among states, once performed, in turn further strengthens the original belief of legal bindingness.

Keywords: customary international law; state practice; opinio juris; dualism; sociology

Suggested Citation

Cho, Sungjoon, Why Do Nations Obey Custom? (May 8, 2023). New York University Journal of International Law and Politics (JILP), Vol. 56, 2023, Available at SSRN: https://ssrn.com/abstract=4441551

Sungjoon Cho (Contact Author)

Chicago Kent College of Law ( email )

565 W. Adams St.
Chicago, IL 60661-3691
United States

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