The quadrilemma: appointing adjudicators in future investor–state dispute settlement

Concern with the selection and appointment of arbitrators has been central in the ‘legitimacy crisis’ surrounding investor–state dispute settlement (ISDS). The regime has been criticized for the outsized role of litigating parties in appointment, absence of transparency in the appointment procedure, potential for conflicts of interests, lack of diversity, and little emphasis on public international law competence. However, attempts to reform the selection and appointment of adjudicators involve confronting dilemmas, requiring trade-offs between different normative values. We therefore introduce a quadrilemma that captures the underlying values of independence, accountability, diversity, and procedural fairness that actors often seek to realize through adjudicatory design. We then set out seven idealized selection and appointment reform options under discussion in the ISDS reform process at UN Commission on International Trade Law (UNCITRAL) (from incremental reform through to new permanent mechanisms and removal of ISDS). The quadrilemma is employed to analyse their advantages and disadvantages of each model. In light of empirical and doctrinal evidence, it is clear that some reform options are more likely than others to optimize the quadrilemma. However, the effects are often conditional and sometimes there is a need for accompanying mechanisms.