Indian Journal of International Law

, Volume 55, Issue 1, pp 85–108 | Cite as

Some considerations regarding “‘Instant’ International Customary Law”, fifty years later

  • Diego Germán Mejía-LemosEmail author
Original Article


In his influential article published in the Indian Journal of International Law fifty years ago, Bin Cheng concluded that the UN General Assembly (UNGA) resolutions on outer space were not legally binding on member states. His conclusion was based on the propositions that (1) custom is mono-elemental, consisting exclusively of opinio iuris; (2) custom may form “instantly”; and (3) UNGA resolutions, albeit lacking binding force, can provide evidence of such “instant” custom. Cheng’s general propositions remain a matter of continuing debate in scholarly literature. It is submitted that mono-elementalism, instead of instantaneity, is at the core of Cheng’s proposition. Nevertheless, Cheng’s mono-elementalism is not borne out by relevant practice. Inconsistency with established practice notwithstanding, Cheng’s main proposition has contributed as a catalyst for debates that continue to elucidate the nature of custom in international law to this day.


International law Sources of law Custom Practice Acceptance as law (Opinio Iuris

Copyright information

© The Indian Society of International Law 2015

Authors and Affiliations

  1. 1.National University of SingaporeSingaporeSingapore

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