International Court of Justice, International Criminal Court :Integrity of International Law

Introduction:
The proliferation of international judicial bodies has raised concerns about the integrity and coherence of international law. For instance, the International Criminal Court (ICC) could, through its decisions, apply principles and rules of international law in ways that diverge from the jurisprudence of the International Court of Justice (ICJ). This article asks whether the ICJ has superior persuasive authority over the ICC in the interpretation and application of the sources of international law—treaties, customary international law, and general principles of law. It hypothesizes that, given the ICJ’s institutional position in treaty interpretation, the identification and determination of customary international law, and the identification of general principles, ICJ jurisprudence exerts superior persuasive authority on the ICC. Existing scholarship has addressed inter-court relations at a theoretical level and has briefly considered aspects of the courts’ respective practices. However, there is no systematic study of the relationship between the ICJ and the ICC, or of the extent to which ICJ jurisprudence influences ICC practice. Accordingly, this article conducts an empirical examination of both courts’ jurisprudence to identify potential ICJ influences on ICC reasoning and to assess the hypothesis.
Methods:
This article employs an empirical method, combining quantitative and qualitative analyses of ICC judicial practice. Here, “empirical” refers to the systematic quantitative and qualitative examination of international judicial decisions to identify structural patterns, recurrent formulations, sequencing, and modes of legal reasoning. Twenty ICC decisions were selected for analysis. All instances relating to the interpretation and application of the sources of international law were identified, compared, and coded. Coding was conducted in three modes: (1) by reference to the specific ICJ advisory opinion or contentious judgment cited by the ICC; (2) by reference to the relevant source of international law and the corresponding ICJ findings; and (3) by reference to patterns of reliance (e.g., repetition, recency, and the placement of ICJ authority within the ICC’s reasoning).
Results and Discussion:
The principal finding is that when the ICC has sought to interpret and apply principles and rules of international law, it has done so by reference to ICJ jurisprudence. The ICJ plays a pivotal role in authoritative treaty interpretation, and the ICC has effectively acknowledged this role by relying on ICJ case law when interpreting instruments such as the Genocide Convention and the United Nations Charter. The analysis further shows that the ICC applies a wide range of customary rules—ranging from immunities to customary rules reflected in instruments such as the 1899 and 1907 Hague instruments—as well as interpretive rules (Articles 31 and 32 of the 1969 Vienna Convention on the Law of Treaties) and general principles of law derived from domestic legal systems and international law, through explicit reference to ICJ jurisprudence. Although the ICC retains full discretion in evaluating evidence and facts, where the ICJ and the ICC address facts arising from the same situation, the ICC refers to the ICJ’s factual findings and, in some instances, even to the dispositif of ICJ judgments. This practice suggests that the ICC treats these elements of ICJ decisions as highly persuasive. Moreover, where the ICC applies principles and rules of international law, it does so in a manner consistent with ICJ jurisprudence and engages relevant ICJ decisions and opinions. For example, when applying the principle of good faith reflected in Article 26 of the 1969 Vienna Convention on the Law of Treaties, the ICC relies on ICJ jurisprudence. While the ICC sometimes cites scholarly writings (doctrine) to support the proposition that treaty-interpretation rules form part of customary international law, these doctrinal references do not undermine the ICJ’s superior persuasive authority, insofar as such scholarship itself relies heavily on ICJ case law. In this sense, doctrinal citations in ICC practice often function as a vehicle for elaborating and systematizing ICJ judicial reasoning. Finally, the ICC’s reliance on ICJ jurisprudence appears purposive, which further supports the claim of superior persuasive authority. “Purposive” reliance refers to patterns that mirror the ICJ’s own approach to precedent: (1) repeated citation of earlier decisions to emphasize the court’s contribution to a rule’s development; and (2) citation of the most recent relevant decision to demonstrate the continuing validity of an established rule. The ICC’s citation patterns—particularly regarding immunities and the right of self-determination—suggest that the ICC recognizes the ICJ’s distinctive role in the development of international law.
Conclusion:
This article demonstrates that, contrary to the view that invoking a court’s theoretical authority is unhelpful, ICJ jurisprudence functions as a superior persuasive authority for the ICC in the determination, interpretation, and application of international law. The ICJ may possess similar persuasive authority for other international judicial bodies, but establishing that broader claim would require separate empirical research of a comparable kind. The article does not argue that empirical methods are inherently superior in international legal research. Rather, given the limited number of studies employing such methods, it contends that empirical analysis is particularly well suited to identifying patterns of practice and institutional behavior and can complement theoretical approaches in developing and substantiating legal arguments.