Proportionality, general principles of law, and investor-State arbitration: a response to Alvarez

International judges and arbitrators make law, as a by-product of their functions as dispute-resolvers, not least, through interpreting norms found in treaties and other recognized sources of law. They do so, increasingly, in dialogues with judges across jurisdictional boundaries. We explore these themes, focusing in particular on how judges and arbitrators have developed general principles of law. Historically, the most important principles materialized in national judicial decisions, as more or less self-evident propositions, beginning in the late 19th century in Europe, the paradigmatic case being the development of the general principles by the French Supreme Administrative Court, the Conseil d’État, and diffusion of this method to other jurisdictions across Europe and globally. It is no exaggeration to say that much of European (and Latin American) public law has been constituted by the development of general principles. In any case, as we have noted, the general principles of law are an authoritative source of law for international judges and arbitrators, and treaty regimes ought to, or must, be interpreted against the background of such principles. How judges do so is the crucial empirical question, and how they ought to do so is the crucial normative question.