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.

中文翻译：

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四难困境：在未来的投资者-国家争端解决中任命仲裁员

对仲裁员的选择和任命的关注一直是围绕投资者与国家争端解决 (ISDS) 的“合法性危机”的核心。该制度因诉讼当事人在任命中的过大作用、任命程序缺乏透明度、潜在的利益冲突、缺乏多样性以及对国际公法能力的不重视而受到批评。然而，改革审判员选任的尝试涉及两难境地，需要在不同的规范价值之间进行权衡。因此，我们引入了一个四元困境，它捕捉了行为者通常通过裁决设计寻求实现的独立性、问责制、多样性和程序公平性的基本价值。然后，我们列出了联合国国际贸易法委员会 (UNCITRAL) 的 ISDS 改革进程中正在讨论的七个理想化的选拔和任命改革方案（从渐进式改革到新的常设机制和取消 ISDS）。四元问题被用来分析每个模型的优点和缺点。根据经验和理论证据，很明显，一些改革方案比其他方案更可能优化四难困境。然而，效果通常是有条件的，有时需要配套机制。根据经验和理论证据，很明显，一些改革方案比其他方案更可能优化四难困境。然而，效果通常是有条件的，有时需要配套机制。根据经验和理论证据，很明显，一些改革方案比其他方案更可能优化四难困境。然而，效果通常是有条件的，有时需要配套机制。