In Dubio Mitius: Advancing Clarity and Modesty in Treaty Interpretation

The principle of in dubio mitius stipulates that if treaty interpreters have doubts about the correct meaning of a provision, they should adopt the interpretation that imposes the less demanding obligation. Although the principle is commonly rejected by scholars, it keeps surfacing in international legal practice. This article describes the history of the principle and provides an overview of its treatment by international courts and tribunals. It then argues that in dubio mitius can be of renewed relevance, now that the legitimacy of international courts and tribunals has become increasingly controversial. The principle recognizes that some questions of treaty interpretation may not have a single permissible answer, even after an application of the customary rules of treaty interpretation, and instead allow for legitimate disagreement or ‘doubt’. In such circumstances, in dubio mitius provides treaty interpreters with a solution, advising them to limit the scope of vague provisions to a normative core that can be deduced with sufficient certainty. In doing so, the principle acknowledges that international courts and tribunals lack the authority to expand international law in the face of legitimate disagreement within and among states.