ABSTRACT
Secondly, there is no single explanation for the manner in which all estoppels operate. Estoppel in all its forms is based on a variety of underlying conceptions, varying from honesty 11 to common sense 12 to common fairness. 13 What emerges just from this short list is that common principles underpinning all estoppel can be identifi ed only at the most rarefi ed levels – that of fairness, justice and so forth. 14 Some academics argue that estoppel arises on the basis of ‘unconscionability’, 15 but acknowledge elsewhere that there is nevertheless a distinction between those forms of proprietary estoppel (let alone the others) which arise variously on the basis of avoidance of detriment, 16 enforcement of promise, 17 or on grounds of mistake. 18 There are various forms of estoppel with boundaries so thin that arguments have been led in the cases for their amalgamation. 19
Nevertheless, despite this doctrinaire position, there has been a powerful argument put by Professor Elizabeth Cooke for the establishment of a single doctrine of estoppel predicated on a concept of good conscience. 20 In general terms, Cooke considers the doctrine of estoppel to be a means of preventing a person from changing her mind in circumstances in which it would be unconscionable so to do. 21 What might be problematic in this conception of estoppel, as Cooke discusses, is deciding on the range of acts and omissions which might be thought ‘unconscionable’ and so render otherwise ordinary, non-actionable examples of people changing their minds into those sorts of changes of mind which are actionable by estoppel. That point can be made in the following way. If estoppels arise on the basis of unconscionability, then there is only a narrow class of acts of what might be ordinarily recognised as unconscionable behaviour which is legally actionable. Therefore, if you promise to telephone me but know when you make the promise that you really do not want to telephone me and that you probably never will telephone me, we might consider that action to have been unconscionable, in that your lying to me is not the act of a completely honest person, but it is unlikely that we would consider it to be legally actionable. Here there is a disjunction between our notion of ‘good conscience’ and our notion of ‘good conscience which is legally actionable’. The fundamental weakness of purporting to base these doctrines on the abstract notions of ‘justice’ or ‘fairness’ is that none of the jurists actually intends to
capture all unconscionable behaviour: only unconscionable behaviour which falls into established legal and equitable categories. 22
The tension here between the historical truth that there are many forms of estoppel and the nagging sense nevertheless that they are all based on similar notions of conscionability is encapsulated in Lord Denning’s apparent shift in emphasis when in 1980 he likened the many forms of this doctrine to ‘a big house with many rooms’ where ‘each room is used differently from the others’, 23 and then in 1981 when his Lordship suggested that while ‘the doctrine of estoppel . . . has evolved during the last 150 years in a sequence of separate developments . . . [a]ll these can now be seen to merge into one general principle shorn of limitations’. 24 It is this drift from separation between many technical forms of estoppel towards the recognition of a central operating principle which Cooke observes. In common with the project of this book in examining the roots of a principle of ‘good conscience’ in much of equity, a principle which draws on the role of the Lords Chancellor as keepers of the monarch’s conscience and from procedural notions of conscentia in early courts of equity, there is a pleasing symmetry in identifying a form of estoppel which can be grounded in the notion that the defendant should be prevented from asserting that y is the case in any circumstance in which it would be unconscionable to deny that x was what the defendant had led the claimant to believe was the case, thus causing the claimant detriment, loss or harm.
