ABSTRACT
There is no single doctrine of estoppel and nor would it be possible to create one out of the existing categories. There is no single explanation for the manner in which all estoppels operate – both those forms considered in this short chapter and the others which are beyond the scope of this book. Estoppel in all its forms is based on a variety of underlying conceptions varying from ‘honesty’ to ‘common sense’ to ‘common fairness’. What emerges from this list is that common principles underpinning all estoppel can only be identified at the most rarefied levels – those of fairness, justice and so forth. Some academics argue that estoppel arises on the basis of ‘unconscionability’ but acknowledge elsewhere that there is nevertheless a distinction between those forms of proprietary estoppel which arise variously on the basis of avoidance of detriment (Lim v Ang (1992)), enforcement of promise (Pascoe v Turner (1979)), or on grounds of mistake (Wilmot v Barber (1880)).
