An estoppel is a legal doctrine which prevents a party from relying upon certain legal rights or facts where the reliance upon such facts or legal rights may be unconscionable. It is a flexible doctrine, both in terms of the circumstances which may fall within its purview and the breadth of relief a tribunal or court may award to satisfy any equity which arises.
It has been given wide international recognition1 and its principles are similarly applicable in the realm of international law where it is considered that sovereign States and private parties ought to be consistent in their attitude to a given factual or legal situation irrespective of its truth.2 However, there is some debate about whether a “strict” or “broad” approach to its application in an international law context is more appropriate.3
Historically, the principle of estoppel was borne out of a common law desire to prevent an unjust departure by a party from an assumption adopted by another as the basis of some act or omission which, unless the assumption is adopted, would operate to that party’s detriment. "Whether a departure by a party from the assumption should be considered unjust and inadmissible depends on the part taken by him in occasioning its adoption by the other party."4
An estoppel may arise when a dispute involves one of the parties making some form of representation by words or by conduct acknowledging a state of affairs. The estoppel operates by precluding the maker of such a representation from asserting the opposite position was true in law or in fact whether or not it actually was. Similarly, in the international investment law context, estoppel could be characterised as a legal response to prevent inconsistent behaviour, which is a concept familiar in all legal systems. International law recognises it through four doctrinal concepts: recognition, acquiescence, waiver and estoppel5 which are rooted in the concept of good faith and preventing inconsistent behaviour by parties to an agreement.
The “strict view” purports that an estoppel arises where one party makes a clear and unambiguous statement and that statement is made voluntarily, unconditionally and is duly authorised by the maker. The party in receipt of the said statement thereafter relies in good faith upon that statement to its detriment or to the advantage of the party making the representation.6
The “broad view” is largely founded upon the same framework although dispenses with the additional requirement of detriment.7 However, in recent times, the International Court of Justice and public international law scholarship8 has more or less consigned any notions of the “broad view” application of estoppel to the history books.9 That being said, in some corners of the international investment law universe, the principle is routinely proffered by parties in disputes to support their position despite the divergence from the International Court of Justice and public international law scholarship, albeit unsuccessfully.10 However, these arguments based on the “broad view” appear to be centred on broader notions of ‘good faith’ and a misunderstanding of the principle of estoppel.
IV. Estoppel at ICSID
One of the first expressions of the doctrine of estoppel is found in the early ICSID cases in the Amco v. Indonesia11 jurisdiction decision which adopted the “strict view” definition of estoppel. Adoption of the “strict” approach in investment disputes has been largely premised upon tribunals’ application of public international law to the dispute and thereby adoption of the International Court of Justice’s characterisation of the issue.12 This is the prevailing view in public international law.13
In contrast, it has been argued that the “broad view” should be adopted because inconsistent behaviour is not to be tolerated and a “State [or party] cannot adopt inconsistent positions in respect of the same state of facts”.14 It has also been argued that the “broad view” encompasses public international law’s recognition of general conceptions of fairness15 and good faith.16 However, it remains that the “broad view” is not the prevailing position. The estoppel doctrine has always required some form of adherence to a particular framework and detriment of some description.
In comparison to common law gestations of estoppel, the international law version of the doctrine is sometimes considered to be imprecise and variable. Additionally, while most tribunals have adopted the “strict view” approach, a few others have endorsed the “broad view” without citing any authority.17
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