Jurisprudential Drift in International Investment Law: From the Minimum Standard to Fair and Equitable Treatment

The meaning of the fair and equitable treatment standard in international investment law remains unsettled. One interpretation ties it to the customary minimum standard of treatment associated with Neer; another treats it as an autonomous and more demanding source of investor protection. States have repeatedly sought to tether FET to the minimum standard, most notably the United States, a principal architect of the investment regime and a major capital exporter. Yet arbitral jurisprudence has tended toward broader interpretations. This Article asks why. It argues that the shift cannot be explained by doctrine, state power, credible commitment, firm pressure, or arbitrator discretion alone. The better explanation is jurisprudential drift: interpretive movement produced within a specialized field of arbitrators, elite counsel, arbitral institutions, and commentators. Open-textured treaty language and arbitral autonomy create interpretive space; investor demand supplies background pressure for capacious protection; and legal counsel and arbitrators benefit, generally but unevenly, from a more complex and protective legal regime. Symbolic capital helps make some broader interpretations focal; reputational enforcement keeps arbitrators and counsel aligned with those interpretations; and secrecy, judicial economy, and peer review supply flexibility, allowing tribunals to manage difficult cases without turning exceptions into a new doctrinal baseline. The Article develops this theory, compares it with existing and reconstructed accounts from law, international political economy, and the social sciences, and evaluates it against the historical, doctrinal, and arbitral record surrounding the rise of the investment regime, the minimum standard, and FET. It concludes that the drift toward autonomous FET reflects a form of transnational legal authority generated through ordinary legal reasoning and coordination within the field of investment arbitration.