The U.N. International Law Commission’s 2018 annual report is being debated from October 22 to 31 before the Sixth (Legal) Committee of the U.N. General Assembly. The report is the product of eleven weeks of work by the Commission in New York and Geneva over this past summer, and contains within it several notable developments.

First, the Commission completed its work on the topic “identification of customary international law,” which consists of sixteen “conclusions” and commentaries. These conclusions concern the methodology for identifying rules of customary international law, and are designed to offer practical guidance, not just for specialists in public international law, but for others as well, including national court judges.

Conclusion 2 confirms the basic two-element approach; that to “determine the existence and content of a rule of customary international law, it is necessary to ascertain” (1) a general practice (2) that is accepted as law (opinio juris). As to the practice that is relevant, Conclusion 4 says that it is “primarily” the practice of States that contributes to the formation of customary rules but that, in certain cases, the practice of international organizations also contributes. By contrast, conduct of other actors—including corporations, non-governmental organizations, or organized armed groups—is not “practice” that contributes directly to the formation of such rules, though it may elicit reactions by States or international organizations that would constitute relevant practice. The uncertain role of international organizations in making such contributions led the Commission, in its commentaries, to indicate that “caution is required in assessing the weight of the practice of an international organization as part of a general practice.”

Conclusion 8 maintains that the “relevant practice must be general, meaning that it must be sufficiently widespread and representative, as well as consistent.” The commentary indicates that “the practice should be of such a character as to make it possible to discern a virtually uniform usage” (Conclusion 8, commentary para. (2)). Moreover, the commentary provides that “an indispensable factor to be taken into account is the extent to which those States that are particularly involved in the relevant activity or are most likely to be concerned with the alleged rule (‘specially affected States’) have participated in the practice” (Conclusion 8, commentary para. (4)).

Conclusion 9 says that the opinio juris element “means that the practice in question must be undertaken with a sense of legal right or obligation,” and should thus “be distinguished from mere usage or habit.” Thereafter, a series of conclusions address certain categories of materials that are frequently invoked in the identification of rules of customary international law:  treaties (Conclusion 11); resolutions of international organizations and intergovernmental conferences (Conclusion 12); decisions of courts and tribunals (Conclusion 13); and teachings of the most highly qualified publicists (Conclusion 14).

Two further conclusions deal with exceptional cases: the persistent objector rule, which provides that where “a State has objected to a rule of customary international law while that rule was in the process of formation, the rule is not opposable to the State concerned for so long as it maintains its objection” (Conclusion 15); and particular customary international law, which are rules of customary international law that apply only among a limited number of States (Conclusion 16). This concept of “particular customary international law” includes bilateral or regional  customary international law (e.g., solely within Latin America), but also a customary rule that operates among a group of States that are dispersed geographically, such as the Commonwealth of Nations that are mostly former territories of the British Empire. Although citing no example, the commentary asserts that “there is no reason in principle why a rule of particular customary international law could not also develop among States linked by a common cause, interest or activity other than their geographical position, or constituting a community of interest, whether established by treaty or otherwise” (Conclusion 16, commentary para. (5)).

Second, the Commission also completed its work on the topic “subsequent agreements and subsequent practice in relation to the interpretation of treaties,” which consists of thirteen conclusions and commentaries thereto. These conclusions seek to explain the role that subsequent agreements and subsequent practice play in the interpretation of treaties, especially with respect to Article 31 of the 1969 Vienna Convention on the Law of Treaties (VCLT). Thus, subsequent agreements and practice are one of several means of interpretation identified in Article 31 (which include with the ordinary meaning of the term of the treaty, its context, and the object and purpose of the treaty), all of which are to be employed as part of a “single combined operation” (Conclusion 2, paragraph 5).

When engaging in the interpretation of a treaty, Conclusion 2 reiterates what is found in the VCLT. Article 31, paragraph 3(a) provides that there shall be taken into account “[a]ny subsequent agreement between the parties regarding the interpretation of the treaty or the application of its provisions,” while paragraph 3(b) provides that there shall be taken into account “[a]ny subsequent practice in the application of the treaty which establishes the agreement of the parties regarding its interpretation.”

The commentary to Conclusion 4 makes clear that for the subsequent agreement or practice to constitute one of the “authentic means” of treaty interpretation found in VCLT Article 31, it must establish an agreement of all the parties to the treaty, not just the practice of some of the parties. To the extent that the subsequent agreement or practice is of only some of the parties, then it may be relevant information for the less significant purposes of VCLT Article 32 (on supplementary means of interpretation), but it does not fall within the scope of Article 31 (Conclusion 4, commentary paras. (4), (9), (16) and (23)). Such an approach, which is consistent with the understandings that existed when the VCLT was adopted, protects treaty parties from being deemed bound by an agreement reached solely by other treaty parties; only if all parties are in agreement will that be viewed as objective evidence of the understanding of the parties as to the meaning of the treaty.

Subsequent practice under Article 31, paragraph 3(b) “may consist of any conduct of a party in the application of a treaty, whether in the exercise of its executive, legislative, judicial, or other functions” (Conclusion 5). A subsequent agreement under Article 31, paragraphs 3(a) and (b), “requires a common understanding regarding the interpretation of the treaty which the parties are aware of and accept. Such an agreement may, but need not, be legally binding for it to be taken into account (Conclusion 10(1)). The commentary indicates that for an agreement to be “common,” it is “sometimes sufficient that the parties reach the same understanding individually, but sometimes necessary that the parties have a mutual awareness of a shared understanding” (Conclusion 10, commentary para. (8)). While the parties must be “aware of and accept” the interpretation, where one party has interpreted a treaty in a certain way, “the awareness and acceptance of the position of the other party or parties may be assumed, particularly in the case of treaties that are implemented at the national level” (Conclusion 10, commentary para. (8)).

Third, the Commission completed the first draft of two further topics, both consisting of 12 draft guidelines and commentaries, on “protection of the atmosphere” and on “provisional application of treaties.” The Commission will now await written comments by governments due in December 2019, before revising and completing these two topics in 2020.

Fourth, progress was also made in developing draft conclusions on “peremptory norms of general international law (jus cogens),” draft principles on “protection of the environment in relation to armed conflict,” and draft articles on “succession of States in respect of State responsibility.” Perhaps the most interesting of these are the jus cogens draft conclusions (see annex to the July 2018 Statement of the Chair of the Drafting Committee). To date these draft conclusions might be grouped into three categories:  a series of draft conclusions that seek to illuminate what peremptory norms are, how they are formed, and how they can be identified (draft conclusions 1 to 9); the consequences of peremptory norms for treaty law, drawing upon rules set forth in the VCLT (draft conclusions 10 to 13); and procedural requirements in the event that a State wishes to invoke a peremptory norm as a ground for invalidity or termination of a rule of international law (draft conclusion 14).

The Special Rapporteur has proposed, but the Drafting Committee has not yet considered, a series of proposals on the consequences of peremptory norms with respect to other sources of international law (including customary international law, unilateral acts of States, and binding resolutions of international organizations), as well as the relationship of peremptory norms to obligations erga omnes and certain other matters. Due to concerns raised in the Commission’s Plenary, the Special Rapporteur has said that he will withdraw proposals asserting: (1) a “duty to exercise domestic jurisdiction over crimes prohibited by peremptory norms”; and (2) the “irrelevance of official position and non-applicability of immunity ratione materiae.” Instead, he intends to propose a provision(s) that will indicate that the Commission’s draft conclusions are without prejudice to the effects that peremptory norms may or may not have within national law with respect to jurisdiction, official position, or immunity.

Fifth, the Commission commenced a debate but otherwise did not make progress with respect to its topic on the “immunity of State officials from foreign criminal jurisdiction.” The Commission, however, added a new topic to its agenda on “general principles of law,” and added two new topics to its long-term work program, meaning that the topics might be placed on the agenda at some point in the future. The first of these topics, “universal criminal jurisdiction,” has been on the agenda of the Sixth Committee for several years, and it is thought that perhaps having the Commission pursue a study of the matter might be of assistance. The second of these topics is on “sea-level rise in relation to international law,” which would address matters relating to the law of the sea, the loss of Statehood, and human rights issues. This second topic would be pursued within a Study Group of the Commission (rather than by means of a Special Rapporteur), and comes on the heels of work by committees of the International Law Association on baselines in 2012 and 2018 and on sea level rise in 2016 and 2018, and associated ILA resolutions in 2018 on baselines and on sea level rise.

Finally, the Commission did not work on a topic that completed its first reading in 2017 and that, after receiving reactions from governments and others, will likely undergo its second reading in 2019: crimes against humanity.