Incidental questions as a jurisdictional problem The limits of subject matter jurisdiction in the practice of international courts and tribunals

In this dissertation, I explore the rules and principles applicable to international courts’ and tribunals’ subject matter jurisdiction over so-called incidental questions or implicated issues. The question of jurisdiction over such incidental questions constitutes a unique dilemma of subject matter jurisdiction, whereby the exercise of a court’s jurisdiction over a given issue depends on the resolution of a preliminary question that lies beyond the confines of that court’s jurisdiction.
Given the absence of a treaty rule or a rule of customary international law governing the conditions and limits of the exercise of incidental jurisdiction, I rely on general principles as well as an analysis of the decisions of international courts and tribunals to identify the relevant applicable law. After reviewing a large body of inter-State decisions from a range of international courts and tribunals, I conduct a detailed examination of six cases that are most pertinent to the question of incidental jurisdiction, scrutinizing not only the final decisions but also the parties’ arguments and, where relevant, dissenting opinions.
By delineating incidental jurisdiction from adjacent concepts relating to the application of external law—such as inherent and implied powers, or the application of external rules based on renvoi provisions—and by offering a detailed account of the modalities of its exercise, the dissertation identifies a narrow but distinct scope for the applicability of incidental jurisdiction.