LibGuides: International Law Research Guide: Opinio Juris

Opinio Juris

Definitions of Opinio Juris

"This phrase (in full, opinio juris sive necessitates ) connotes an element in the formation of international custom, expressed in art. 38(1)(b) of the I.C.J. Statute as ‘a general practice accepted as law’. ‘It is not sufﬁcient to show that States follow habitually a certain course of conduct, either doing or not doing something. To prove the existence of a rule of international customary law, it is necessary to establish that States act in this way because they recognize a legal obligation to this effect’: Schwarzenberger and Brown, A Manual of International Law (6th ed.), 26." - Grant, John P., et al.

Opinio Juris - Grant, John P., et al. Parry and Grant Encyclopaedic Dictionary of International Law, Oxford University Press, Incorporated, 2009.

"The two constituent elements in customary international law are state practice and opinio juris sive necessitates , or opinio juris . These elements are expressly stated in article 38, paragraph 1, subparagraph b, of the Statute of the International Court of Justice and have been widely accepted by international judicial bodies. The Court referred to these elements in numerous cases...

Opinio juris is traditionally derived from state’s opinions, but exactly how a state expresses its opinion in relation to an act that is or is not in accordance with the rule alleged to be international law is not always clear. On the one hand, such manifestations of opinion might come from the statements of senior state officials or the official statements of states in an international body such as the United Nations General Assembly. On the other hand, statements of opinio juris might be the result of widely supported resolutions, especially one such as the Declaration on Principles of International Law concerning Friendly Relations and Cooperation among States in Accordance with the Charter of the United Nations (UNGA Res. 2625 (XXV) adopted 24 October 1970), which expressly states it is recognizing principles of international law. Evidence of opinio juris might include diplomatic pronouncements, votes, or other such expression of views by states. Some terms recognized by the International Court of Justice as expressing more than an opinio simpliciter include “ recognition ,” “conviction,” “sense of duty,” and “consciousness,” according to O. Elias, “The Nature of the Subjective Element in Customary International Law,” ICLQ 44, no. 3 (July 1995): 501, 511. It is important that the expression of opinio juris be directed toward an act and concern a sense of legal obligation for it to contribute to forming customary international law." - Doebbler, Curtis F. J.

Opinio Juris - Doebbler, Curtis F. J. Dictionary of Public International Law, Rowman & Littlefield Publishers, Incorporated, 2018.
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Bouvier Law Dictionary Opinio Juris (Opinio Juris Sive Necessitatis)

Understanding Opinio Juris

Celebrating 50 Years Of Scholarship: Reflections On Key Articles From The First Five Decades: A Mystery No Longer? Opinio Juris And Other Theoretical Controversies Associated With Customary International Law, 50 Isr. L. Rev. 299
Offering a current reflection on Raphael Walden's 1977 article, 'The Subjective Element in the Formation of Customary International Law, this contribution seeks to illustrate that considerable clarity has been achieved over the decades with regard to several long-standing questions associated with customary international law, not least those surrounding opinio juris. Accumulated practice and constructive scholarship have supplied insights into, and indeed answers to several of the controversies that have bedevilled the theory of this central source of international law. While it may inherently defy exact formulations, and some theoretical questions remain, customary international law is thus today not only as present in the international legal system as it has always been but is also better understood.
State Intent Under International Law, 3 Cardozo Int'l & Comp. L. Rev. 403
The question of legislative intent has long been a topic of intense scholarly focus in the United States. There has also been a recent uptick in discussion of executive branch intent with the filing of high-profile lawsuits predicated upon allegations of improper motives. However, there has been no corollary effort to unpack the concept of state intent at the international level, where it arises with respect to such varied questions as how to understand the scope of a state's consent, whether a state should be deemed to be negotiating in good faith, and whether a state has engaged in genocide. This Article seeks to fill this gap, offering a taxonomy of state intent under international law. It also offers a potential explanation for why one might wish to apply different models of state intent, distinguishing, for instance, between the use of intent to rule out "excluded reasons" for acting (as is the case under U.S. law with respect to discrimination) and the use of intent to better understand what is being communicated (as is sometimes the case with respect to statutory interpretation). Finally, the Article draws an analogy to inquiries into corporate intent under U.S. domestic law to chart a tentative path forward toward better understanding the intent of states.
Introduction Custom At The Heart Of International Law, Brigitte Stern. , 11 Duke J. Comp. & Int'l L. 89
Celebrating 50 Years Of Scholarship: Reflections On Key Articles From The First Five Decades: The Subjective Element In The Formation Of Customary International Law, 50 Isr. L. Rev. 310
A Theory Of Constructive Interpretation For Customary International Law Identification, 39 Mich. J. Int'l L. 301