From a Fortuitous Transplant to a Fundamental Principle of Law?

The doctrine of legitimate expectations (LEs) is now considered a backbone principle of international investment law (IIL), particularly of the fair and equitable treatment standard (FET). Open any recent textbook of IIL and you will find discussion on LEs as one of the core principles. However, if one takes a step back, one may see that the notion of legitimate expectations simply appeared in early investment cases ‘out of thin air’. This contribution will argue that, while LEs’ appearance in IIL practice may be viewed as contingent, its ascendance into the principal doctrine of substantive IIL with specific parameters is neither entirely accidental nor random. The use and specific parameters of the doctrine have been allowed and facilitated by both the indeterminate and semantically ambiguous legal form of IIL obligations, and by a specific historical context in which the notion became prominent. The consequence of the argument can be appreciated at two levels. First, it can be argued that even without the contingent ascendance of the notion of LEs, the field of IIL would likely have taken up a similar substantive trajectory. Second, this argument sheds light on questions about how a more substantial change in the regime might be effected, instead of merely reforming certain aspects of the regime without affecting its current premises, structure, substance, and teleology. By doing so, the contribution underlines the difficulties in articulating plausibly what would have made a difference in a particular legal regime.