Public international law and comparative law have so far been regarded as largely distinct fields, with little to no overlap between them. The degree of separation between the two disciplines is rendered in particularly stark relief by the absence in practice or scholarship of any real inquiry into the relationship between comparative law on the one hand and customary international law and general principles of international law on the other. (1) Some eminent international lawyers go so far as to claim that it would be both unnecessary and unrealistic to have recourse to comparative law in the context of the identification of customary international law and general principles of law, pointing to the case law of the Permanent Court of International Justice and the International Court of Justice, which, according to them, "show[s] a clear disinclination towards the use of the comparative method." (2)
To some degree, this situation is a matter of curiosity since international law and comparative law share the same openness to the world and are both confronted by the diversity of domestic legal cultures and state practice. Given this state of affairs, initiatives aimed at bridging the gap between international law and comparative law (which is the purpose of "comparative international law") merit close attention. (3)
At the same time, however, the relevance and claimed novelty of such initiatives need to be approached with caution and viewed in their proper context. It may be the case that the combination of both disciplines eventually proves more harmful than helpful to international law. Multiculturalism, which lies at the heart of the concept of "comparative international law" and conveys the idea that international law could be approached differently depending on the culture of each country, society, or peoples, is not a neutral approach. The mere concept of comparative international law could be seen as giving too much weight to the cultural aspect in international law by taking as given that there are differing approaches to international law (something that is not necessarily self-evident) and by putting more emphasis on cultural and national identities than on the more secular, ecumenical figure of the state (including the principle of sovereignty and its various expressions and reflections in concrete rules), which seems to remain more influential in the elaboration, interpretation, and application of today's international law. (4) More importantly, one may wonder whether the mere concept of comparative international law does not in fact entail a catch-22: If one admits that there are different approaches to international law (i.e., a real comparative international law), is there still room for an "international law"? (5) It is one thing for international law to tolerate, as it does, multiculturalism in the domestic sphere (6) and quite a different thing for multiculturalism to have an impact on the international plane through the manifestation of different conceptions of international law. (7)
Admittedly, the risk of diluting international law by relying on comparative international law is not so great when comparative international law consists in academic studies that explore potential divergences among national conceptions of international law. But comparative law is not only an academic exercise; it is also used by practitioners, for practical purposes. (8) In international law, comparisons between domestic practices are particularly important for the identification and formation of customary international rules, which depend heavily on the assessment of existing state practice and opinio juris. To the extent that it can have a concrete effect on international law in force or in statu nascendi, the notion of "comparative international law" needs to be approached with caution. In practice, it is not an easy task to strike the right balance between the need for international rules and the imperative to avoid "negating] cultural relevance in identifying common values." (9) The formation and development of international law presuppose the taking into account of existing approaches, however diverse they might be, and their encompassment by rules of international law that are both common and applicable to all states. Such a conciliation of diversity and unity is a challenging task, one which comparative international law also has to face.
Fortunately, such attempts are not wholly novel, and lessons can be learned from the past. Judge Owada has noted that, in the encounter of Japan with the West in the mid-nineteenth century, Japanese intellectuals
tried to identify this concept of "the law of nations" as one which should have its rational meaning as a concept of universal validity, and tried to understand it in the context of their own intellectual tradition.... They tried to comprehend the meaning of what was "specific" by identifying what was "universal" in that specificity. To borrow the words of Levi-Strauss, a well-known social anthropologist who started the structuralist school of anthropology, the scientific approach of structuralism in anthropology should consist in the "quest for the invariant, or for the invariant elements among the superficial differences." It is my personal belief that this approach of "the quest for the invariant and universal elements among the superficial differences" should represent the essence of the process of Asia's approach to the "Community of Civilized Nations." (10) This approach provides a relevant blueprint for a successful combination of comparative law and international law.
Concrete examples are found in the work of international institutions over many decades of dealing with comparative international law (well before the expression was coined) in the process of identifying international law. This is the case with the International Law Commission (ILC or Commission), which was instituted in 1947 to assess the degree of uniformity of state practice and the extent to which it is possible to overcome divergences. (11) As early as 1949, there was a clear view that "if the task of the International Law Commission were confined to fields with regard to which there is a full measure of agreement among states, the scope of its task would be reduced to a bare minimum." (12) In other words, the Commision's raison d'etre lies in the existence of at least some degree of difference between states' practice, which needs to be overcome by codifying or progressively developing "one" international law. The Commission can, in that regard, be seen as a fruitful laboratory for assessing how comparative international law has operated in practice over the last seventy years. Accordingly, the present analysis will explore the extent to which the work of the Commission can provide useful insights about the benefits, drawbacks, and practical difficulties of resorting to comparative international law within international law (thus avoiding undermining it) in the process of establishing what international law is or should be.
In particular, I will show that there is a "vital necessity of maintaining the interplay of distinct legal cultures in the making of international law" and that such a process, which permits mutual tolerance and favors the acceptance and enforcement of international law, "may entail the salutary effect of assimilating or lessening the existing differences"; (13) that this task requires reliance on representative international organs, which have to develop specific tools to formulate international rules in harmony with national or regional cultural approaches or concerns; and that this task may necessitate the formulation of international rules (at least universal ones) "in as general terms as possible," in order to guarantee sufficient flexibility. (14) The recourse to comparative international law within international law may accordingly eventually result in quite a subtle sharing of tasks and relationships between international law and domestic law. Part I of the present study will elaborate on these main observations by identifying the institutional ingredients that are required in order for comparative international law to obtain a sufficiently representative conception of international law. Part II will then explore the main tools used by the Commission on the substantive plane to draft common rules on the basis of existing and possibly divergent state practice or opinio juris. The focus will be placed in that regard on customary international law insofar as general principles of international law have for the most part never been considered by the Commission as a field to be explored on its own--presumably because both codification and progressive development of international law require the Commission to base its proposal at least on some emerging state practice (i.e., on some customary law in statu nascendi), while general principles of international law are rather used as a measure of last resort when no other source can be relied on.
According to Article 1, paragraph 1, of its Statute, the Commission "shall have for its object the promotion of the progressive development of international law and its codification." (15) The dual functions of the Commission are implicated in both the pre- and post-formation stages of international law. Codifying international law consists of identifying existing customary international rules. Progressive development of international law, on the other hand, entrusts the Commission with a quasi-legislative function, the expression being defined by the Statute of the Commission as "the preparation of draft conventions on subjects which have not yet been regulated by international law or in regard to which the law has not yet been sufficiently developed in the practice of states." (16) In other words, the Commission is charged with assessing state practice in order to identify what...