Author: Victor Stoica

Required knowledge: Link

Learning objectives: Understanding XY.

This is where the text begins.[1] This template follows our style guide. Please take into account our guidelines for didactics. If you're wondering how to create text in Wikibooks, feel free to check out our guide on how to write in Wikibooks.

Advanced: Example

This is your advanced content. You can create this text box using our template "Advanced". How to do this is described here.


Example for example topic: This is your example.


Question Circle.svg Test your knowledge in our learning area.


Just replace the content above and below with your content.

A. IntroductionEdit

Customary international law is unwritten law. In other words, it is tacit agreement. Prior to World War II, customary international law represented the main mechanism through which international law was created. During those days, the repeated behaviours of states were sufficiently capable of creating legal norms, which, after they emerged, contained rights and obligations, which were binding in nature. In this context, certain opinions exist in the sense that "a careful examination of history suggests that to a large degree publicists and powerful nations ignored inconvenient state practice and generated customary international law norms based on prior assumed values or perceived self-interests irrespective of the general acceptance of a norm".[2]

Today, customary international law is one of the main sources of international law, next to treaties. References to article 38 paragraph 1 of the Statute of the International Court of Justice,[3] which contains the sources of international law that the Court may apply when it decides upon the disputes that are submitted before it, are used as anchors for the understanding the meaning and content of customary international law. What is currently clear is that "the binding force of international customary law rests on the implied consent of states".[4]

The generally accepted interpretation of customary international law implies that a two-pronged test should be performed in order to determine the existence and content of a rule. First, practice among states must exist and, second, this practice must be accepted as law. Second, the practice must be performed out of a sense of an exiting legal obligation. In other words, if a sufficient number of states perform actions or inactions, or issue declarations, in a generally consistent manner, which is sufficiently widespread and representative, with the sense that they are doing so because they have an international legal obligation, a norm of customary international law may bloom. Framing customary international law as such has been labeled as the orthodox perspective on the formation of customary international law.[5] Controversy surrounds this view, especially because the interaction between practice (referred to as the objective element) and its acceptance as law (referred to as the subjective element) is not easily distilled. The traditional limitations regarding the exclusion of other entities from the formation of customary international law (for example, international organisations) raised either favourable or unfavourable opinions from states and international publicists.

Thus, the interpretation and application of customary international law as a source of law is not yet clear. The practice of international courts and tribunals, including the International Court of Justice, does not necessarily provide in depth clarifications regarding a coherent interpretation of this source of international law. One the main reasons for this rather muddy understanding of customary international law is that, as opposed to treaties, the formation of customary international law does not follow a predictable path, or a specific procedure. It would seem that customary international law appears at one point in time but customary international law forms by leaning on certain rules.

For these reasons, international scholarship addressing the understanding of customary international law has recently multiplied. Further, international institutions involved in the codification and progressive development of international law, such as the International Law Commission of the United Nations have included the identification of customary international law on their agenda and issued, in 2018, the Draft conclusions on Identification of Customary International Law.[6]

The strict identification of practice and the distinctions between actions and declarations of states contribute to the difficulties in identifying the subjective element, which has been assimilated to beliefs (or feelings) of States, is noticeable when looking towards the direction of the International Court of Justice or of the International Law Commission of the United Nations. It has been argued, in this sense, that "it would be a mistake to believe that power is the only relevant factor in the emergence of CIL. The role of ideas and beliefs is significant".[7] Further, the International Court of Justice also referred to the beliefs and feelings of States, which crystallise opinio juris as a constituent element of customary international law, throughout its jurisprudence, in cases such as the North Sea Continental Shelf Cases or in the Asylum Case, respectively. Illustratively, in the North Sea Continental Shelf, the Court concluded that belief is needed for the existence of opinio iuris to be demonstrated.[8] Even so, the International Court of Justice has failed to clarify what constitutes opinio juris and how it interacts with the practice of states in order to determine the content of customary international law. This contributes to the lack clarity and consensus that revolves around the formation and identification of customary international law today is still not clear as "different meaning and weights are often assigned to the two elements of states practice and opinio iuris".[9]

This chapter does not suggest a new conceptual framework regarding the identification and formation of customary international law. Nor does it intend to resolve the apparent controversies regarding the subject. It rather intends to describe the contemporary manner in which customary international law is formed and identified.


B. Constitutive Elements of Customary LawEdit

As mentioned above, for customary international law to be formed two elements should be present: I. A general practice and II. Opinio iuris, meaning the general practice is performed out of a belief that a legal obligation exists in this respect. The following sections shall address the content of the two elements.

I. General PracticeEdit

Article 38 of the Statute of the International Court of Justice prescribes that the Court, when deciding the disputes that are submitted to it, the Court will apply "international custom, as evidence of a general practice accepted as law."[10] The first issue that should be determined when addressing the existence of customary international law is, thus, the indispensable element of general practice.

General practice is the material or objective element of customary international law because the existence of this element does not depend on the perception of states, international organisations or other entities that exist in today's international society. In other words, when practice is performed it may be, often times, observed. For example, when a state repeatedly transits with its naval ships a certain maritime zone, that is practice. More about practice, below.

1. What does "practice" mean?Edit

First of all, it is generally accepted that state practice is primarily relevant for the creation of customary international law. Draft Conclusion 4 of the ILC Draft conclusions on identification of customary international law confirms this view when concluding that "The requirement of a general practice, as a constituent element of customary international law, refers primarily to the practice of States that contributes to the formation, or expression, of rules of customary international law." .[11] The International Court of Justice, in the judgment it issued in the Military and Paramilitary Activities in and against Nicaragua provided the same conclusion, in this sense, that "to consider what are the rules of customary international law applicable to the present dispute … it has to direct its attention to the practice and opinio juris of States".[12]

This finding, among others has led certain commentators, and the representatives of certain states, to conclude that only states may generate practice relevant for the formation of customary international law. However, as presented in the following sections, other entities are also relevant for the creation of customary international law, such as international organisations or international courts and tribunals. For the moment, it is important to determine what activities may be considered practice, for the purposes of identifying customary international law. The question that needs an answer, at this juncture, is thus: "What counts as practice?".

States behave in the international arena through various mechanisms which are created and disseminated by multiple stakeholders. High officials, such as Heads of State or Ministers, municipal courts and tribunals or legislative bodies have the possibility of developing practice. However, not any actions performed by these entities are capable of creating the material element of customary international law. Scholars have concluded, in this sense, that a distinction should be made between actions and statements/declarations.[13] It is often the case that actions involve a predominantly legal perspective while statements and declarations involve a predominant political perspective, the latter being less capable of creating practice.

To summarise, certain actions may be considered practice while mere political statements/declarations might not. This is not to say that the latter are without any value for the creation of customary international law but that their legal relevance, from the perspective of norm creation, is rather secondary.

a) ActionsEdit

State practice is generally understood through the perspective of the acts/actions performed by the executive branch. It is also generally accepted that certain high officials have the vocation to represent the state in the international arena: the President, Prime Minister, Minister of Foreign Affairs, and other executive and legislative bodies. For example, if a national court maintains its jurisprudence regarding a particular aspect, that has international implications, that body of judgments may contribute to the crystallisation of practice.

The International Law Commission confirms, through Draft Conclusion 5, that practice may manifest in situations in which states exercise multiple activities, including through their "executive, legislative, judicial or other functions."[14] This list, provided by the ILC, is open ended and leads to the argument that any act or action of states, through their organs, may constitute state practice. This is to say that practice shall be analysed holistically, on a case by case basis by looking in the direction of the state as a whole, with all its relevant institutions and officials. Illustratively, diplomatic correspondence on a certain issue, along with political declarations of a high official along with the positions maintained throughout the negotiation of a treaty on the same subject matter, may constitute practice.

It is worth mentioning, at this juncture, that states and their organs are abstract concepts which exercise their functions through people, mandated in this respect by the state (for example through the Constitution), which is, in turn, structured and mandated by its citizens, through the voting process. Consequently, and interestingly, it is the individual/s which represent the organs of states or states themselves, which is/are capable of creating customary international law. Who qualifies as an individual which may represent the State in its external affairs depends on the national legislation of each State. In Romania, the President, Prime Minister and Minister of Foreign Affairs have the competence to represent the state (including by negotiating the provisions of treaties) without the need to present full powers.[15] What is essential is that the people who may represent the state and, consequently, who may generate practice, act in their official capacity.[16]

Several acts or actions may illustrate the formation of practice as an element of customary international law. The classic example regarding customary international law is maritime law, which when it first emerged was "almost entirely customary international law"[17]. The North Sea Continental Shelf Cases,[18] in which the exercise of certain fishing rights in economic zones of the coastal states was addressed by the Court, is relevant from this perspective. Other examples include "actively seizing foreign vessels, actually expropriating foreign property or sending satellites into orbit",[19] as elements of practice.

Not only physical acts (exercising fishing by states or seizing foreign vessels) may constitute practice as an element of customary international law, but legal acts may have serve the same purpose.[20] If states enact legislation through which fish are protected within 200 miles off their costs, there is potential for the creation of a rule of customary international law in this respect.[21]

To summarise, action as an element of customary international law is a vague concept which is not necessarily capable of clarification through norm creation, for example by providing an exhaustive list of what can be considered an action. This means that "any conduct of the State, whatever the branch concerned and functions at issue"[22] may contribute to the formation of customary international law. The same conclusion may not be applied to inaction, as practice.

b) InactionsEdit

Sometimes, omissions may also represent state practice.[23] In other words, sometimes silence produces legal effects in the international arena and, further, is capable of creating legal norms. Draft Conclusion 6 issued by the International Law Commission regarding the identification of customary international law confirms that practice may, "under certain circumstances, include inaction".[24] So, not every inaction constitutes practice for the purposes of creating customary international law and certain distinctions should be made in this sense. The question that would need an answer is therefore: "which omissions may constitute practice"?

The answer that seems to be confirmed by the doctrine is that only the omissions which are clear in their scope may fulfil the role of practice as an element of customary international law. In this sense, omissions must be carefully interpreted so as to determine what was the true intention of the State that did not perform a particular actions. The caution in addressing omissions as practice under customary international law is demonstrated by the practice of international courts and tribunals. In this respect, the Permanent Court of International Justice, in the Lotus Case did not address the formation of customary international law because the abstention in question was ambiguous.[25] The International Court of Justice was braver in its analysis of inaction as evidence of practice. In the Temple of Preah Vihear Case, the Court concluded that inaction may generate rights and obligations only if that state must and can act, but it does not. The Court decided that "it is clear that the circumstances were such as called for some reaction, within a reasonable period, on the part of the Siamese authorities, if they wished to disagree with the map or had any serious question to raise in regard to it. They did not do so, either then or for many years, and thereby must be held to have acquiesced."[26]

In other words, inaction may generate customary international law if there exist "intention and deliberateness".[27] The Court confirmed its finding from the Temple of Preah Vihear Case in other judgments, such as the in which it held that "silence may also speak, but only if the conduct of the other State calls for a response."[28] The Commentary of the Draft Conclusions further provides examples in this sense: "abstaining from instituting criminal proceedings against foreign State officials; refraining from exercising protection in favour of certain naturalized persons; and abstaining from the use of force".[29]

c) StatementsEdit

Finally, statements of representatives of states may not represent state practice. As initially concluded by Prof. Anthony D'Amato[30] and further confirmed by Anthea Roberts[31] statements are rather included under the subjective element of international law, opinio iuris. Conclusion 10 issues by the International Law Commission confirms that "public statements made on behalf of States"[32] represent one of the multiple forms of evidence as acceptance as law. As such, the relevance of public statements for the creation of customary international law will be treated below, under the section entitled "Accepted as Law (Opinio Iuris)".

2. What does "general" mean?Edit

Part of the international scholarship accepts that generality of practice means that "all or almost all of the nations of the world engage in it".[33] Even if this conclusion has certain merit, the same authors conclude that it is impossible to determine if 190+ states have engaged in a certain practice,[34] which, as mentioned above is complex and can be manifested through a wide range of activities or abstentions and, further, is rarely virtually homogenous.[35]

This is the reason for which conclusion 8 of the ILC Draft Conclusions on Identification of Customary International Law provides that for practice to be general is must be "sufficiently widespread and representative as well as consistent".[36] The standard imposed by the International Law Commission is, thus, lower than the one related to the unanimity or majority of practice. As such, generality implies three different concepts which must be met cumulatively. The Commentary of the ILC Draft Conclusions does not further qualify what these three concepts mean but mentions that "no absolute standard can be given for either requirement",[37] argument that leads to the conclusion that their content is addressed on a case by case basis, leaving international courts and tribunals a wide degree of appreciation for the consideration of the existence of a rule of customary international law.

a) Sufficiently widespreadEdit

Widespread is generally understood as "existing or happening in many places and/or among many people".[38] The International Court of Justice confirmed the relevance of the concept in "Maritime Delimitation and Territorial Questions between Qatar and Bahrain", in which it concluded that it was not aware of the existence of uniform and widespread practice that could lead the Court to conclude that a customary rule regarding the appropriation of low-tide elevations.[39] In "Questions relating to the Obligation to Prosecute or Extradite" the Court concluded, with respect to the imperative norm regarding the prohibition of the use of torture that it is "grounded in a widespread international practice and on the opinio juris of States".[40]

The International Court of Justice has not endeavored to define the concept, nor does the Commentary of the Draft Conclusions on Identification of Customary International Law. It just quotes the North Sea Continental Shelf cases, in which the Court concluded that the practice in question must be “both extensive and virtually uniform”,[41] or “settled practice”.[42] However, these standards are not universal and they cannot be, nor were they, relevant in all cases in which the application of customary international law was at stake. The Commentary goes even further and mentions that "no absolute standard can be given for either requirement".[43] The only clarification provided is that practice is sufficiently widespread when it is not "contradictory or inconsistent".[44]

b) Sufficiently representativeEdit

Representative is generally understood as "typical of, or the same as, others in a larger group of people or things".[45] At first glance, it might seem that the concept of "representative" has common features with the concept of "widespread", especially because the number of entities participating in the creation of customary international law is relevant in both cases. However, certain distinctions should be drawn between the two.

The International Court of Justice has not necessarily addressed what "representative" means. However, in the North Sea Continental Shelf, the Court concluded that "a very widespread and representative participation" would be sufficient to demonstrate the existence of customary international law resulting from a convention. The Commentary of the ILC Draft Conclusions on Identification of Customary International Law provides that for the practice to be representative it must take into consideration the "various interests at stake and/or the various geographical regions."[46] As such, it would appear that while "widespread" implies a quantitative standard, representativeness implies a qualitative standard.

In this sense, the notion of "specially affected states" seems relevant. The Commentary of the ILC Draft Conclusions sheds light into the relevance of this concept, in the following terms:

"In assessing generality, an important factor to be taken into account is the extent to which those States that are particularly involved in the relevant activity or most likely to be concerned with the alleged rule have participated in the practice. It would clearly be impractical to determine, for example, the existence and content of a rule of customary international law relating to navigation in maritime zones without taking into account the practice of coastal states and major shipping states"[47]

c) ConsistencyEdit

Consistency is generally understood as "the quality of always behaving or performing in a similar way, or of always happening in a similar way".[48] This standard implies that practice should manifest stability over time.[49] As such, if the behaviors of states fluctuate over time, it would be difficult, if not impossible, to identify a general practice.[50]

This element is very much important when addressing the persistent objector doctrine. Conclusion 15 of the ILC Draft Conclusions on Identification of Customary International Law[51] provides that if a State expressly objects to a rule of customary international law when that rule is in the process of formation, the said rule will not be applied regarding the state that objected. The distinction is relevant, because potential objections of states which are performed after customary international law was formed are no longer relevant. In other words, states that did not object during the formation of customary law do no longer have the right to object when they must comply with the created rules. Authors have concluded, in this sense that, "If allowed to formulate objections to avoid immediate compliance costs, states might be tempted to corrode the mutual long-term benefits of the custom."[52]

II. Accepted as Law (Opinio Iuris)Edit

For customary international law to exist, first, a general practice must exist, but it must also be performed out of a sense of a legal obligation. In other words, states must believe that their actions, inactions, or statements are performed or issued because they are compelled through international law to do so. Further, the Commentary of the International Law Commission mentions that customary international law cannot exist in the absence of opinio juris, by arguing that “the presence of only one constituent element does not suffice for the identification of a rule of customary international law.”

The salience of the subjective element, which has been assimilated to beliefs (or feelings) of States, is noticeable when looking towards the direction of the International Court of Justice or of the International Law Commission of the United Nations. The International Court of Justice referred to the beliefs and feelings of States, which crystallize opinio juris as a constituent element of customary international law, throughout its jurisprudence, in cases such as the North Sea Continental Shelf Cases or in the Asylum Case, respectively. Nevertheless, the International Court of Justice has failed to clarify what constitutes opinio juris and how it interacts with the practice of states in order to determine the content of customary international law.

Conclusion 9 of the ILC Draft Conclusion on Identification of Customary International Law provides that a general practice accepted as law is not the same as „mere usage or habit”. Further, the Commentary of the Commission regarding the above mentioned Conclusion clarifies the meaning of opinio juris and provides that states must „believe” or „feel” that they are legally compelled to act.

C. Who creates custom?Edit

I. StatesEdit

Article 38 (1) b. of the Statute of the International Court of Justice prescribes that the Court will decide in accordance with international law by applying „international custom, as evidence of a general practice accepted as law”. The mentioned provision does not explicitly mention that states, or international governmental organizations, or both, are the only entities that can participate in or influence the formation of customary international law.

Nevertheless, what is also traditionally accepted is that states and international governmental organizations are the main subjects of international law. Certain authors confirm that the two entities are the only subjects of international law, strictly speaking and, as such, the only ones that can contribute to the formation of customary international law.

The practice of the International Court of Justice confirms that States are the entities that contribute to the formation of customary international law. Illustratively, in the Asylum Case, the ICJ did not find that customary international law existed because the practice of states was not uniform and constant. In the North Sea Continental Shelf, the ICJ concluded in the following terms: „State practice, including that of States whose interests are specially affected” is relevant for the formation of customary international law. Further, in Military Activities in and Against Nicaragua the Court referred to the practice of States and to opinio iuris of States while in Jurisdictional Immunities it also determined that „State practice of particular significance is to be found in the judgments of national courts faced with the question whether a foreign State is immune, the legislation of those States which have enacted statutes dealing with immunity, the claims to immunity advanced by States before foreign courts and the statements made by States”.

Thus, the jurisprudence of the International Court of Justice confirms that states are involved in the formation of customary international law. The former President of the Court, Judge Yusuf concluded in his Statement before the Sixth Committee that customary international law, at least in accordance with the „old approach” was primarily based on the consent of states, while other entities, such as the United Nations provide states with a forum through which they engage on different issues, including the formation of customary international law.

The ILC Commission, within its Draft Conclusions regarding the identification of customary international law confirms that states contribute to its formation. In this respect, Draft Conclusion 4 paragraph 1 provides that „the requirement of practice refers primarily to the practice of States” while the Commentary of the Draft Conclusion further clarifies that „States play a pre-eminent role in the formation of customary international law.” The wording does not exclude other enteritis that might contribute to the formation of international law. Thus, international organizations may also influence the formation process.

II. International OrganizationsEdit

Not only States may contribute to the formation of customary international law. As secondary subjects of international law, international organizations may also influence the manner in which customary international law is generated. Out of the four entities, the international organization is the only one that manifests a double role: direct and indirect. As such, first, international organizations may influence how state contribute to the formation of international law (indirect influence) or, in situations in which international organizations behave like states they directly contribute to the formation of customary international law.

1. Indirect influenceEdit

International organization may influence the formation of customary international law by impacting the conduct of their member states. As such, international organizations may be considered as "catalysts of state practice".[53] In other words, it has been argued that international organizations shape what states do and think.[54] Illustratively, the European Union regularly participates in international legal forums, such as the Sixth Committee of the United Nations or the International Law Commission, bodies of the UN which address and discuss the norms of international law.

The ILC Articles on State Responsibility confirms this possibility through the Commentary of the Draft Conclusions which provides that "resolutions adopted by international organization or at intergovernmental conferences, even when devoid of legal force of their own, may sometimes play an important role in the development of customary international law"[55] The issue of indirect influence is not necessarily controversial and is recognized by the international community. This is not the case with direct influence.

2. Direct influenceEdit

The International Law Commission, through Draft Conclusion 4 para. 2 confirms that international organisation may directly influence the formation of customary international law. As such, the mentioned Conclusion provides that „in certain cases the practice of international organisations also contributes to the formation or expression of rules of customary international law.” Further, the Commentary of the Draft Conclusions clearly delineates direct influence from indirect influence as it mentions that the above mentioned paragraph concerns "practice that is attributed to international organisations themselves, not practice of States acting within or in relation to them". The European Union is often considered as being such an organisation which, in certain circumstances, or for certain competences, acts in the international arena like a State.

The direct influence of international organisations regarding the formation of customary international law is not as clear cut as the indirect influence. Illustratively, the United States of America have criticised the approach of the International Law Commission and mentioned that "it is axiomatic that customary international law results from the general and consistent practice of States followed by them out of a sense of legal obligation".[56]

Even so, the doctrine rather supports the view that international organisations have the posibility to directly influence the formation of customary international law. Further, the majority of states endorsed the approach of the ILC and "affirmed that at least some international organisations can sometimes contribute directly to the formation of customary international law"[57]

III. International Courts and TribunalsEdit

IV. Individuals, Transnational Corporations and Non-Governmental OrganizationsEdit

D. Special Customary International LawEdit

I. Jus Cogens NormsEdit

One of the limits is represented by jus cogens norms which are globally widespread, and are part of the concept of general customary international law. These customary norms "are considered so vital that they cannot be contracted out of by individual states";[58] they have the highest degree of generality.

II. Regional Customary International LawEdit

At the opposing end of the spectrum rests regional (or particular) customary international law. In 1950, in the Judgment issued in the Asylum Case the Court did not exclude the general possibility of regional customs to exist, even if it concluded that the Colombian Government did not prove the existence of such a custom.[59] In 1984, in the judgment issued in the Case concerning Military and Paramilitary Activities in and against Nicaragua, the Court appeared to agree that regional customary international law, "particular to the inter-American legal system",[60] exists. Conclusion 16 of the Draft Conclusions on Identification of Customary International Law qualified regional customary international law and

E. Conclusion how is custom created?Edit

"It is, thus, not important for the Court to develop a coherent methodology of identifying customary international law. Instead, identification strategies may differ depending on the circumstances of each individual case and the preferences of the affected parties"[61]

I. Traditional and Modern ApproachesEdit

Further ReadingsEdit

  • Source I
  • Source II

ConclusionEdit

  • Summary I
  • Summary II

Table of ContentsEdit

Back to home page

Part I - History, Theory, and Methods

Part II - General International Law

Part III - Specialized Fields

FootnotesEdit

  1. The first footnote. Please adhere to OSCOLA when formating citations. Whenever possible, provide a link with the citation, ideally to an open-access source.
  2. J. Pattrick Kelly, Customary International Law in Historical Context, in Brian D. Lepard (ed.), Reexamining Customary International Law, Cambridge University Press, 2017, 47, available at: https://www.cambridge.org/core/books/abs/reexamining-customary-international-law/customary-international-law-in-historical-context/02A51C93813D4889EC5BC79120B3E396
  3. Statute of the International Court of Justice, available at: https://www.icj-cij.org/en/statute
  4. Vincy Fon,Francesco Parisi, Stability and Change in International Customary Law, University of Chicago, available at:https://www.journals.uchicago.edu/doi/pdfplus/10.1086/656058
  5. Jutta Brunnée, Customary International Law Symposium: Making Sense of Law as Practice (Or: Why Custom Doesn’t Crystallize), available at: http://opiniojuris.org/2020/07/07/customary-international-law-symposium-making-sense-of-law-as-practice-or-why-custom-doesnt-crystallize/
  6. Draft conclusions on identification of customary international law, with commentaries, International Law Commission, available at: https://legal.un.org/ilc/texts/instruments/english/commentaries/1_13_2018.pdf
  7. B.S. Chimni, Customary International Law: A Third World Perspective, American Journal of International Law, 112(1), 28
  8. North Sea Continental Shelf, Judgment, I.C.J. Reports 1969, p. 3, at p. 44, para. 77, available at: https://www.icj-cij.org/public/files/case-related/52/052-19690220-JUD-01-00-EN.pdf
  9. B.S. Chimni, Customary International Law: A Third World Perspective, American Journal of International Law, 112(1), 2
  10. Statute of the International Court of Justice, available at: https://www.icj-cij.org/en/statute
  11. https://legal.un.org/ilc/texts/instruments/english/commentaries/1_13_2018.pdf
  12. Military and Paramilitary Activities in and Against Nicaragua (Nicaragua v. United States of America), Merits, Judgment. I.C.J. Reports 1986, p. 14, para 184, 98, available at: https://www.icj-cij.org/public/files/case-related/70/070-19860627-JUD-01-00-EN.pdf
  13. Anthea Roberts, Traditional and Modern Approaches to Customary International Law
  14. Draft Conclusions on Identification of Customary International Law, available at:https://legal.un.org/ilc/texts/instruments/english/commentaries/1_13_2018.pdf
  15. For a brief definition of the concept of "full powers" please see Anthony Aust, Modern Treaty Law and Practice, Cambridge University Press, 2007, available at: https://www.cambridge.org/core/books/abs/modern-treaty-law-and-practice/full-powers/CC43B04EF5073D42380460A72AA832AD
  16. Draft conclusions on identification of customary international law, with commentaries, International Law Commission, available at: https://legal.un.org/ilc/texts/instruments/english/commentaries/1_13_2018.pdf
  17. DR Rothwell, T Stephens, The International Law of the Sea (2010) 22; R Barens, D Freestone, DM Ong, ‘The Law of the Sea: Progress and Prospects’ in D Freestone, R Barens, D M Ong (eds), The Law of the Sea. Progress and Prospects (2006)
  18. International Court of Justice, North Sea Continental Shelf cases (Federal Republic of ­Germany v. Denmark; Federal Republic of Germany v. the Netherlands), Judgment, 20 ­February 1969, 1969 General List Nos. 51 and 52
  19. Jan Klabers, International Law, 2013, p. 50
  20. Laurence Boisson de Chazournes, Qu’est-ce que la pratique en droit international?, available athttps://archive-ouverte.unige.ch/unige:36443
  21. Ibid.
  22. ILC Draft Conclusions on Identification of Customary International Law, Available at: https://legal.un.org/ilc/texts/instruments/english/commentaries/1_13_2018.pdf
  23. Rudolf Bernhardt, Customary International Law, in 1 Encyclopedia of Public International Law, 898, 900
  24. https://legal.un.org/ilc/texts/instruments/english/commentaries/1_13_2018.pdf
  25. https://files.pca-cpa.org/pcadocs/bi-c/2.%20Canada/4.%20Legal%20Authorities/RA-97%20-%20Formation%20of%20Customary%20International%20Law,%20M.%20Mendelson%20(1998).pdf
  26. Case concerning the Temple of Preah Vihear (Cambodia v. Thailand), Merits, Judgment of 1.5 June 1962: I.C. J. Reports 1962, p. 6, 23, available at: https://www.icj-cij.org/public/files/case-related/45/045-19620615-JUD-01-00-EN.pdf
  27. Dustin A. Lewis, Naz K. Modirzadeh, Gabriella Blum, "Quantum of Silence: Inaction and Jus ad Bellum", Harvard Law School, Program on International Law and Armed Conflict, 17, available at: https://pilac.law.harvard.edu/quantum-of-silence-paper-and-annex//part-ii-what-we-mean-by-silence#_ftn46
  28. Sovereignty over Pedra Branca/Pulau Batu Puteh, Middle Rocks and South Ledge (Malaysia/Singapore), Judgment, I.C.J. Reports 2008, p. 12, para. 121, 50-51 available at: https://www.icj-cij.org/public/files/case-related/130/130-20080523-JUD-01-00-EN.pdf
  29. International Law Commission, Draft conclusions on identification of customary international law, with commentaries, 133, available at: https://legal.un.org/ilc/texts/instruments/english/commentaries/1_13_2018.pdf
  30. ANTHONY A. D’AMATO, THE CONCEPT OF CUSTOM IN INTERNATIONAL LAW 49 (1971)
  31. https://deliverypdf.ssrn.com/delivery.php?ID=781006013127075084082070107120095109058027047084089074075021095109110104010081068076100027018126119126005099097020003101077068106017028001034082009115072005083011048064000072083127105015113002073080091125067027122070121086127125020106115072098104026&EXT=pdf&INDEX=TRUE
  32. https://legal.un.org/ilc/texts/instruments/english/commentaries/1_13_2018.pdf
  33. Jack L. Goldsmith, Eric A. Posner, A Theory of Customary International Law, John M. Olin Law & Economics Working Paper No. 63, 1999, 7, available at https://papers.ssrn.com/sol3/papers.cfm?abstract_id=145972
  34. Ibid.
  35. Niels Peteresen, The International Court of Justice and the Judicial Politics of Identifying Customary International Law, The European Journal of International Law, 2017, vol. 28, no. 2, 377.
  36. Draft Conclusions on Identification of Customary International law, available at: https://legal.un.org/ilc/texts/instruments/english/commentaries/1_13_2018.pdf
  37. Draft Conclusions on Identification of Customary International law, available at: https://legal.un.org/ilc/texts/instruments/english/commentaries/1_13_2018.pdf
  38. Cambridge Dictionary, available at:https://dictionary.cambridge.org/dictionary/english/widespread
  39. Maritime Delimitation and Territorial Questions between Qatar and Bahrain (Qatar v. Bahrain), Merits, ICJ Reports (2001) 40, at 101–102, para. 205.
  40. Questions relating to the Obligation to Prosecute or Extradite (Belgium v. Senegal), Judgment, I.C.J. Reports 2012, p. 422, para. 99, 39, available at: https://www.icj-cij.org/public/files/case-related/144/144-20120720-JUD-01-00-EN.pdf
  41. North Sea Continental Shelf, Judgment, I.C.J. Reports 1969, p. 3, para. 74, 44, available at: https://www.icj-cij.org/public/files/case-related/52/052-19690220-JUD-01-00-EN.pdf
  42. Ibid. para 77, 45.
  43. Draft Conclusions on Identification of Customary International Law, available at: https://legal.un.org/ilc/texts/instruments/english/commentaries/1_13_2018.pdf
  44. Ibid.
  45. https://dictionary.cambridge.org/dictionary/english/representative
  46. https://legal.un.org/ilc/texts/instruments/english/commentaries/1_13_2018.pdf
  47. Draft Conclusions on Identification of Customary International Law, available at: https://legal.un.org/ilc/texts/instruments/english/commentaries/1_13_2018.pdf
  48. https://dictionary.cambridge.org/dictionary/english/consistency
  49. https://www.journals.uchicago.edu/doi/pdfplus/10.1086/656058
  50. https://www.journals.uchicago.edu/doi/pdfplus/10.1086/656058
  51. https://legal.un.org/ilc/texts/instruments/english/commentaries/1_13_2018.pdf
  52. https://www.journals.uchicago.edu/doi/pdfplus/10.1086/656058
  53. Jed Odermatt, Interantional Law and the European Union, Cambridge University Press, 2021, p. 43.
  54. Kristina Daugirdas, International Organisations and the Creation of Customary International Law, EJIL, Vol. 31, no. 1, 202
  55. ILC Draft Conclusions, Commentary, 148
  56. https://www.ejiltalk.org/wp-content/uploads/2019/02/US-Views-on-ILC-Draft-Conclusions-on-CIL.pdf
  57. Kristina Daugirdas, International Organisations and the Creation of Customary International Law, EJIL, Vol 31, no. 1
  58. Roozbeh B. Baker, Customary International Law in the 21st Century: Old Challenges and New Debates, The European Journal of International law, 2010, Vol. 21, Issue 1, 177.
  59. Colombian-Peruvian asylum case, Judgment of 20 November 1950, I.C.J. Reports 1950, p. 266, at p. 277.
  60. Military and Paramilitary Activities in and against Nicaragua (see footnote 663 above), at p. 105, para. 199.
  61. Niels Petersen, The International Court of Justice and the Judicial Politics of Identifying Customary International law, The European Journal of International law, 2017, Vol. 28, no. 2, 366