Towards a Predictable Standard of Proof in International Adjudication

María Elisa Zavala Achurra*

Benjamin Salas Kantor* *†

Evidence plays a key role in the resolution of disputes. While international courts and tribunals have developed principles and rules to address evidence production and the burden of proof, the application of the standard of proof remains elusive and somewhat enigmatic. The standard of proof is of paramount importance as it delineates the evidentiary test that the party bearing the burden of proof must meet in order to prevail in a dispute. In practice, however, its application often boils down to which side’s evidence the tribunal finds more persuasive, with scant methodological guidance. This article advocates for a structured approach to address the standard of proof in international adjudication. It posits a two-step methodology for international tribunals to consider when establishing facts by applying the standard of proof required for a given claim. The proposed approach aims to increase the predictability of third-party adjudication while acknowledging that certain flexibility on evidentiary matters is both inherent and desirable for a well-functioning international dispute-resolution system.

* Adjunct Professor, Pontificia Universidad Católica de Chile; Associate, Cleary Gottlieb Steen & Hamilton LLP, New York; Law Degree (Pontificia Universidad Católica de Chile), LL.M. (Harvard Law School).

** Lecturer in Law, Columbia Law School; Associate Legal Officer, International Court of Justice, The Hague; Law Degree (Pontificia Universidad Católica de Chile), LL.M. (Columbia Law School).

† The authors thank Jonathan Shapiro, Benjamin Boston, and the rest of the Columbia Journal of Transnational Law’s editorial team for their valuable assistance and feedback. Any views expressed in this Article are entirely those of the authors and do not reflect the views of Cleary Gottlieb Steen & Hamilton LLP or the International Court of Justice.