Rethinking the predominant purpose test under Article 18 ECHR—lessons from the détournement de pouvoir à la française

The doctrine of détournement de pouvoir illustrates how legal transplants from domestic legal orders can shape the European Convention on Human Rights (ECHR) system. Originating in French administrative law, its influence on Article 18 ECHR highlights both the promise and pitfalls of legal transplants. Although Article 18 lay dormant for decades, its recent activation has strengthened the Convention’s capacity to address rule of law violations. Yet the ECtHR’s adoption of détournement de pouvoir—particularly through the ‘predominant purpose’ test in Merabishvili—reflects a broad and somewhat mechanical borrowing. The Court did not fully consider the doctrine’s French nuances, instead holding that Article 18 is violated only where the illegitimate aim outweighs the legitimate one. This approach generates ambiguity. In this sense, the test functions as a ‘legal irritant’. A more tailored adaptation, through transposition and tuning, is necessary to ensure that domestic legal concepts enhance rather than disrupt the ECHR system’s legal coherence and effectiveness.