Interlegality as a Theory of Sustainable Adjudication

The term “fragmentation of international law” aptly captures the complexity of contemporary global legal challenges. While often seen as problematic, fragmentation can also reflect positive trends like pluralization, diversification, and even democratization. Regardless of perspective, it underscores a critical issue for today’s global legal systems: maintaining equilibrium among competing rationalities, whether territorial, economic, or systemic. Across various international legal regimes (e.g., WTO, ECHR, and climate change frameworks), states, NGOs, and individuals often present claims based on differing rationalities. For instance, the ECtHR has ruled on states’ responsibilities to safeguard citizens’ rights to a healthy environment in the context of climate change, while the ITLOS and ICJ have provided advisory opinions on states' obligations to prevent environmental harm. A pressing question arising from this is how international and domestic courts should address diverse rationality claims stemming from distinct legal systems or regimes. For example, can the ECtHR, a human rights court, legitimately issue binding judgments on states’ accountability for climate change-related harms to human rights? This paper addresses such normative concerns by proposing a method of legal adjudication rather than focusing solely on legal interpretation. It treats interpretation as integral to adjudication, which it views as the broader process of resolving disputes over the application of general norms to specific cases. Accepting global legal pluralism as a reality, the paper argues that courts should incorporate all relevant legal arguments in their decisions, including those originating from other legal regimes. Drawing on the theory of intersectionality, it suggests that intersecting legal arguments from various rationalities can expose methodological blind spots. Interlegality, in this context, is proposed as both a theory of adjudication and a perspective informed by intersectionality. The paper begins by exploring why international courts should adopt interlegal adjudication. In the absence of a global political authority to resolve conflicts among legal regimes, there is a moral imperative for courts to use interlegal reasoning to avoid contradictory judgments. This aligns with the principles of international rule of law, which demands foreseeability, predictability, and consistency in legal decisions. Clear guidance is essential for stakeholders—states, NGOs, companies, and individuals—who otherwise risk being subject to conflicting directives. Thus, the principles of the international rule of law provide a compelling rationale for interlegal adjudication. Then the paper illustrates this approach through recent climate change cases such as Urgenda, Neubauer, and Shell. These cases demonstrate how courts rely on a mix of legal norms from different regimes, including international agreements (e.g., the Paris Agreement and ECHR), scientific evidence (e.g., IPCC reports), and domestic constitutional provisions, to hold states and corporations accountable. By integrating such diverse sources, interlegal adjudication offers a pathway to addressing complex global challenges while fostering coherence and legitimacy in international legal systems.