Is arbitral investment case-law on expropriation precedential in a legally relevant sense? Orthodox approaches are marked by agreement on a narrow set of arguments, namely that international law is not a common law and arbitral awards do not have stare decisis power, that jurisprudence is hugely important and tribunals rely on it, and that there must therefore be a sort of de facto system of precedents in operation. In effect, ‘factual importance’ is fashioned into a source of legal authority. However, few arguments are given as to why this transfer from fact to law would occur and they do not provide a foundation for a general legal value for precedents. Yet the weight of arbitral jurisprudence is both too great to ignore and too helpful in discovering what ‘’ means in a pragmatic sense. Precedents are statements about general norms; outside the common law, judge-made law is merely an interpretation of a general norm in a judgment. Not even a constant tradition of decisions can turn such a statement into a norm.

In this chapter, the method of ‘frame-determination’ for IIA expropriation clauses is applied and three limits of the actus reus condition of typical IIA expropriation clauses are identified. (1) On the macro-structural level, concerning the interaction of IIA clauses with the rest of international law, facile references to customary international law are shown to be problematic: ‘’ in IIAs does not refer to a customary norm of certain validity and great specificity. (2) On the micro-structural level, the necessity of treating direct and indirect expropriation as fully equivalent is structurally inherent in typical IIAs. (3) All legality conditions are equal and cannot be doubled in the actus reus of indirect expropriation. The structure of typical IIA clauses does not support the majority of arguments based on ‘police powers’ or on a ‘right to regulate’.

Does judicial interpretation of IIAs produce epistemic ‘authority’? Interpretation can mean both the process of finding out what texts mean and guidance to the concretisation of abstract general norms in individual instances. In the second sense, interpretation is subconsciously used to narrow the freedom of deciders; a range of interpretative tools is used to generate a quasi-formal unity of meaning across IIAs. Systemic integration is the most used and most potent tool. It enjoins us to assume that meanings are identical, but this is baseless: taking into account external rules could just as easily be the basis for a divergence. However, customary law is less certain and precise than assumed. From the perspective of peer-accepted reasoning-before-decision, the interpreter takes meanings, not external rules, into account. Arbitral tribunals in fact interpret IIAs in light not of a customary norm but of other investment tribunals’ understanding of the meaning of other treaty norms. On that perspective, there is no distinction between interpretative tools. Interpretation cannot unify investment law because it does not change the law, only certain brute facts.