The overlap between judging and arbitrating dominated the eighth Sciences Po Mayer Brown lecture in Paris, where speakers scrutinised whether the two functions are genuinely distinct or whether the legal community has simply failed to develop coherent standards for managing their interaction. The event, founded by Dany Khayat of Mayer Brown and Professor Diego P. Fernández Arroyo of Sciences Po Law School, was moderated by Isabella Lacreta and framed around the theme of "cross-pollination" between courts and arbitral tribunals.
The keynote, delivered by Professor Makane Moïse Mbengue of the University of Geneva and Sciences Po under the title "Judges, Arbitrators and Judges-Arbitrators: Virtues and Constraints of Transnational Justice," centred on the notion of a transnational adjudicating community — those who decide disputes across domestic courts, international courts and arbitral tribunals. In that community, legal reasoning, procedural techniques, reputations and ethical concerns circulate freely and increasingly across borders.
Testing an Assumed Distinction
Professor Mbengue posed three questions: whether a functional frontier separates international judges from arbitrators, whether an axiological frontier does so, and whether the judge-arbitrator can serve as a vehicle for cross-pollination. The keynote challenged a common assumption that judges are constrained, public, neutral and virtuous, while arbitrators are viewed through the vocabulary of bias, conflicts of interest, double-hatting, repeat appointments and professional incentives.
Criticism of investor-State arbitration and intra-EU investment arbitration has sharpened these concerns, with arbitrators often portrayed as a small community exposed to issue conflicts and cognitive bias. Yet the lecture exposed an asymmetry: practices treated with suspicion in arbitration appear in comparable forms within international courts without drawing the same reproach. The composition of international courts, including the International Court of Justice, is inseparable from State nomination, election and diplomatic support.
The ICJ's 2020 Restrictions
The discussion turned directly to the restrictions the ICJ adopted in 2020, which moved away from what had been a relatively common practice of Court members sitting as arbitrators. Speakers accepted that independence and impartiality plainly matter, but questioned whether a bright-line prohibition was the most appropriate response. Such a rule protects the Court from reputational risk and avoids case-by-case assessment, but it also limits the participation of judges whose expertise may be valuable and narrows opportunities for cross-pollination.
A Historical Continuity
The keynote traced the tension back to the Hague Peace Conferences of 1899 and 1907 and the drafting of the Statute of the Permanent Court of International Justice in 1920, showing that the debate between separation and complementarity is not new. It cited the ICJ's 1953 Nottebohm judgment as recognising the positive influence of the arbitrator-judge, and pointed to Max Huber — whose Island of Palmas and British Claims in the Spanish Zone of Morocco awards later resonated in ICJ jurisprudence on territorial sovereignty, effectivités, intertemporal law and State responsibility — as proof that international law has developed through circulation between awards and judgments.
A broad convergence emerged: the aim should not be to suppress cross-pollination but to discipline and channel it. Speakers favoured principled regulation over categorical exclusion, identifying genuine risk scenarios — party appointments by States appearing before the same judge, overlapping issues creating structural conflicts, and repeat appointments generating economic dependence — while recognising that the public/private divide cannot carry the full analytical burden, given that investment and inter-State arbitration frequently decide questions with public consequences.