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A Thorough Insight on ILC’s Approach to Evidence of Customary International Law

Updated: Nov 3, 2022

Customary International law is considered an important source of law under the International legal system. Customary International law means those rules of International law that are derived from and reflect a general practice accepted as law. This understanding of customary international law has been affirmed by the Special Rapporteur of the International Law Commission, Sir Michael Wood. The important elements in identifying customary international law include state practise and opinio juris. Sir Michael Wood emphasised that to prove a principle as a part of customary international law it is crucial that the two elements are prevalent and evidence is presented of their prevalence to support the claim so made about the principle.

The International Law Commission published a report in 1950 which analysed ways and means to make the evidence for customary international law more readily available. It primarily emphasised on how the evidence is sought in a variety of materials including documents for state practice and judicial decisions on matters of international law as per the article 24 of the statute of the commission. However, article 24 of the statute of the commission does not clarify anything with regards to the nature of the documents. The report of the International law commission has given out examples of documents and materials for evidence of customary international law. The report explains that texts of international instruments, decisions of national and international courts, national legislations, diplomatic correspondence, opinion of legal advisors and practice of international organisations form a major chunk of the materials and documents for evidence.

The status of the suggestions of the 1950 Report in 2020

The central question discussed by the report of the International law commission was about the availability of documents and materials forming evidence for customary international law. One of the important points raised by the report includes the concern of maintaining physical compilation of the documents and materials available such as constitutions of the states and their legislations. The problem is not limited to compilation but also extends to keeping it up to date since national laws keep changing with time. However, this problem has been resolved to a large extent with time. The United Nations now maintains a digital database of national legislation and policies regarding the relevant matters of International law including but not limited to piracy, terrorism and maritime laws. It is easily available for people at large as well due to the presence of the data on online websites of the United Nations which also provides links to the national legislation and policies related to the relevant matters. The report also suggested a summary or digest of decisions of the international court of justice. The digest of the international court’s cases and their summaries are available with the codification division of United Nations office of legal affairs. These are prepared with the help of the registry of the International Court of Justice. It contains electronic versions of published volumes, covering the period 1948–2017, as well as of summaries of documents issued by the Court since 2018, which are yet to be published in this series.

The problem, however, persists with respect to the publication of decisions of national courts. The report of the International Law commission suggested back in 1950 that the General Assembly should suggest the states to form digests of the decisions and operations of their national courts and make them available to the United Nations. The objective behind it was to simply ensure that the practices of the states can be analysed or understood from the decisions of the national courts. The decisions of national courts have also been given significantly important value in terms of evidence for practice. The importance was particularly appreciated in Jurisdictional immunities of the state case (Germany v. Italy: Greece Intervening). It was said that the practice was sought from the judicial decisions of the national courts. The latest report on the subject came in the year 2018 when the commission discussed ‘Identification of customary international law’. The recommendations of the commission included a suggestion to the General Assembly to notify states of the desirability of publishing digests of their national practice for the development of customary international law. Even after the suggestions by the commission, almost all states are lacking on this front and haven’t taken any concrete steps to furnish the said publication. It is thus important that the General Assembly calls upon states to form digests of the decisions and reports of their respective National Courts and make them available since it is practically impossible for the International organisation to keep tabs on the operations of the national courts of the member nations. However, it is practically possible for states to implement such a suggestion since in most countries digests are already prepared by individual lawyers or organisations. The states can either sanction one of them or prepare a state-sanctioned digest which can then be made available for the United Nations. The digests are not supposed to contain information about all cases being dealt with by the courts, but only the cases which are relevant to some matters of International Law as emphasised in the International law commission report.

Another major problem that hasn’t been resolved even after its mention in multiple International Law Commission reports is the publication of diplomatic correspondence. It simply means the summary or digest of the diplomatic communications made by the states. According to the International Law Commission, such communications are vital to understanding state practice and customs followed. The report published in 1950 explains that such digests or compilations prove to be useful and cited as an example the digest of the European States published in Fontes Juris Gentium covering events from 1856 to 1878. It is a request or suggestion which hasn’t been accepted yet and states have not published digests of the diplomatic correspondence. The commission suggested in the latest report on the matter in 2018 that states should be encouraged by General Assembly to do the same for a better understanding of state practice and making available the evidence of customary international law. It should be ensured that such a request is made to the states by the General Assembly at the earliest possible to ensure progress towards fulfilment of article 24 of the statute of Commission.

The report published in 1950 also suggested the practice of international organisations as important evidence for customary international law. Owing to the recognition, the United Nations General Assembly mandated the repertory in its resolution 796(VIII) of 1953. The repertory of the United Nations covers its practice from the year 1946 onwards. The suggestion made in the 1950 report has been brought to fulfilment by the organisation after the General Assembly mandated the same through a resolution it passed.

Another suggestion made by the International law commission in 1950 was about the possibility of an international convention for the exchange of official documents. It was implemented in 1958 by UNESCO. However, the convention can be scrutinised owing to the current problems. The problem with the convention is in Article 2 primarily. Article 2 of the convention defines the official documents in clause 1. The article does not specifically mention digests or publications of diplomatic correspondence as official documents which are why there is no obligation on the state parties to produce the same today. The report published in 1950 had already highlighted the importance of diplomatic correspondence as evidence; however, even after the emphasis on the same in the report, UNESCO ignored the same while preparing the convention on the subject matter. Clause 2 of the same article also leaves the decision of what constitutes a document for an exchange on the state itself. This allows the state to possibly leave any documents out of the scope of the convention even though they might be of importance and relevance to the International Law Commission for the progressive development of customary international law.


The measures suggested in the 1950 report can still be applied since the approach of the law commission hasn’t changed as reflected in the 2018 report on the same subject. The commission still recognizes the role of diplomatic correspondence and decisions of national courts as important evidence of customary international law which suggests that there still is a need for states to publish the same or make them readily available. As states haven’t taken an initiative to work on publications related to diplomatic correspondence for many years now, it seems appropriate to consider the revision of the Convention on International Exchanges under the ambit of Article 21 and a general conference of the UNESCO should be called for the same. The revision can help in adding the required evidence and creating an obligation on states to publish the same for better development of customary international law. The United Nations General Assembly should also be called upon to suggest the states or call their attention on specifically these two pieces of evidence as the role of General Assembly has proven helpful in the past with some other evidence. The states should be suggested to make it readily available for the United Nations in addition to other states as maybe finalized under the convention. It might seem a harsh step to some, however, the Commission has approached the situation lightly for the past 70 years now. There has been little to no development on the front of diplomatic correspondence and digests of national courts. For progressive development of customary international law and the work of International Law Commission, it is important to create obligations on states to do the same to ensure the fulfilment of the Article 24 of the statute of Commission.


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