Methodologies for the identification of customary international law from the perspective of a government legal advisor
By Kristi How
Published on 23 November 2022
In this short blog post, I aim to provide my views on the methodologies for the identification of customary international law (CIL) from the perspective of my personal experience as a government legal advisor. However, as stated by Judge Tanaka in his dissenting opinion in North Sea Continental Shelf, determining the existence or lack of State practice and opinio juris is ‘a delicate and difficult matter’. Given the necessarily imprecise exercise that one must undertake to assess the existence of general and consistent practice that is accepted as law, I cannot claim to represent all government legal advisors, or my own government for that matter, on this issue or cover the plurality of perspectives in the identification of CIL. In this sense, I have approached this topic from the starting position that a government legal advisor is an individual, who in the identification of CIL will inadvertently be shaped from their individual perspectives or bias. This also means that a legal advisor’s method for the identification of CIL is not necessarily the same as that undertaken by their State, albeit their legal advice may inform the State’s approach.
Identification of State Practice
One way to identify general and consistent State practice is to adopt an empirical approach. A government legal advisor may have some unique advantages to this empirical approach by virtue of the fact that he or she can rely on having access to foreign missions and technical agencies documents to conduct research and gather evidence. That said, this empirical approach is necessarily limited in scope. Since it is simply not possible to survey every State, the legal advisor will necessarily have to rely on his or her subjective judgment to determine whether enough evidence has been gathered. Even if such a survey were possible, it may be difficult to achieve uniform consensus on the existence of or content of a CIL. Faced with incomplete evidence, a legal advisor will therefore have to rely on limited information and extrapolate, by a process of logical induction, the likely existence of a CIL rule. Given that the analysis is inductive in nature, there will necessarily be an element of subjective value judgment on the part of the legal advisor in determining the weight of the information before him or her.
Concurrent to carrying out an exercise for the identification of general and consistent State practice, a legal advisor would also keep in mind their State’s practice in this area, if such practice exists. The identification of national practice may be an easy exercise if such practice is well documented. Unfortunately, this exercise can be unexpectedly challenging in the face of changing administrations and archiving practices, and the inevitable effects of time on documents and human memory. Therefore, a legal advisor may be relegated to relying on an approximation of what is likely to have been his or her State’s practice, taking into account certain longstanding policy positions. The legal advisor may also need to take into account the practice of domestic courts, which may be at odds with the government’s position on matters of international law. The latter situation is famously reflected in the Italian Constitutional Court’s treatment of the International Court of Justice’s decision in Jurisdictional Immunities of the State.
Opinio juris
Opinio juris can be difficult to ascertain as well. However, a legal advisor may try to deduce the general existence of a belief in the existence of a legal obligation from multilateral treaties or statements made in international fora like the UN General Assembly. Whether such texts support the existence of opinio juris will depend on a variety of factors, such as whether they are phrased in declaratory terms or the extent of State support for the propositions contained within. That said, the weight to be ascribed to each factor and each instance of purported proof of opinio juris will be affected by the legal advisor’s subjective judgment.
In addition to the above, legal advisors may also rely on subsidiary means for the determination of rules of international law, as reflected in Article 38(1)(d) of the Statute of the International Court of Justice. Subsidiary means do not in and of themselves constitute a formal source of international law. They are however useful for providing a court’s or publicist’s distillation of the evidence supporting the existence of a particular CIL rule underpinned by consistent State practice, and the content of that rule. Depending on the factual background underpinning the legal advisor’s search for CIL, judicial decisions could be ascribed a particular weight given the tendency of courts, especially in common law systems, to rely on prior judicial pronouncements as part of their decision-making.
Occupying the role of a governing advisor
While this post uses the term “identification”, this should not be understood as suggesting that what a legal advisor is trying to do is uncover an objective immutable truth. To start with, the determination of the existence of general and consistent State practice requires a legal advisor to make a subjective value judgment on the weight of the evidence before them. This value judgment will also be influenced by the aim of the international lawyer undertaking the identification exercise. Such aims may include their duty to their State, and the need to take into account the development of international law as a whole.
In view of the above observations, a question worth asking is whether the legal advisor is truly identifying CIL or is merely collecting evidence in the case that there is a need to justify the existence of CIL, for instance, in the case of a dispute. As Martti Koskenniemi argues, “competence” in international law ‘is not the ability to reproduce out of memory some number of rules, but a complex argumentative practice in which rules are connected with other rules at different levels of abstraction and communicated from one person or group of persons to another so as to carry out the law jobs in which international lawyers are engaged.’
A legal advisor must therefore accept that, in their attempt to identify CIL, there may not be clear evidence establishing the existing of a CIL rule or evidence that clearly explains the content of such CIL rule. As such, the legal advisor’s identification exercise is often one where the goal is the establishment of reasonable and persuasive legal arguments to support the existence or lack of a CIL rule. The legal advisor’s chosen methodology for the identification of CIL, including the weight that should be ascribed to the evidence in support of or challenging the evidence of a particular CIL rule, will then necessarily evolve to fulfil that goal.
Author’s bio: Kristi How is a State Counsel in the International Affairs Division of the Attorney-General’s Chambers and an Adjunct Lecturer at the National University of Singapore School of Law. The views expressed in Kristi’s contributions to this blog are solely her own and do not necessarily reflect the views of any institution with which she is or has been affiliated.