Kenny JA summarised the principles involved in the following terms (at 14):
'The principles which govern an application for rectification of a contract on the ground of unilateral mistake can be briefly stated. If (1) one party, A, makes an agreement under a misapprehension that the agreement contains a particular provision which the agreement does not in fact contain; and (2) the other party, B, knows of the omission and that it is due to a mistake on A's part; and (3) lets A remain under the misapprehension and concludes the agreement on the mistaken basis in circumstances where equity would require B to take some step or steps, depending on those circumstances, to bring the mistake to A's attention; then (4) B will be precluded from relying upon A's execution of the agreement to resist A's claim for rectification to give effect to A's intention [here her Honour cited Taylor v Johnson and numerous other authorities]. Whether or not the mistake must be one which operates in favour of B or merely to the detriment of A is not entirely clear... .'
50 The cases to which I have referred were cases in which equitable remedy by way of rescission or rectification was granted to redress unconscionability emerging from or founded on unilateral mistake. There is no reason why other equitable remedies should not be available where the elements justifying relief exist. The essential elements are, first, that one person enters into a contract under a serious mistake about its content in relation to a fundamental matter; second, that the other party is aware that circumstances exist indicating that the first person is entering into the contract under a serious mistake about the content or subject matter of that aspect of the contract; and, third, that the second party deliberately sets out to ensure that the first party does not become aware of the existence of the mistake, either by positive acts or omitting to bring it to their attention.
51 In the present case, the first question is whether the plaintiff, when agreeing on 13 January 2004 to become co-purchaser with the defendant of the Wyoming property, knew that the effect of what she was doing was to put the defendant in a position where she would become the owner of an undivided one-half interest in the property. The plaintiff's evidence is that she did not know and did not understand that; and that she was shocked and upset when she later found that the defendant owned such an interest. The defendant's evidence is that Ms Marigliano explained the matter fully to the plaintiff. Ms Marigliano corroborates this, although her corroboration is somewhat dulled by her statement that, on her understanding, the plaintiff "can't speak - communicate verbally". If the evidence stopped there, the plaintiff might be seen to have failed at the first step in seeking to make out a case of unilateral mistake. But there is, in this case, an unusual factor to be taken into account. I refer to the plaintiff's deafness and the uncertainty there must be as to what she received and comprehended when a trained and experienced interpreter was not available to assist. Things Ms Marigliano heard the defendant relay to the plaintiff by distinct, mouthed speech may not have been understood. And, particularly in light of the plaintiff's habit of nodding when things are being relayed to her, Ms Marigliano may well not have appreciated that things the plaintiff appeared to comprehend were, in reality, not comprehended at all. The passages of cross-examination at paragraphs [36] to [38] above would reinforce this possibility.
52 There is, however, no need for me to come to any firm conclusion on this first aspect of the plaintiff's unilateral mistake case because I am satisfied that the plaintiff fails at the second stage of the inquiry - that is, the need to show that the defendant was aware of circumstances indicating that the plaintiff was acting under a serious mistake as to the identity of her co-purchaser. The defendant's evidence is that Ms Marigliano explained the matter of the defendant's half-ownership to the plaintiff and that the plaintiff appeared to understand. This is consistent with Ms Marigliano's evidence. Objectively, therefore, the defendant must be taken to have been unaware of (and to have had no reason to suspect the existence of) any relevant mistake under which the plaintiff was in fact labouring. That being so, the plaintiff's unilateral mistake case cannot succeed.
53 The second basis on which the plaintiff puts her constructive trust claim in respect of the defendant's interest in the property is that the circumstances in which the defendant obtained the interest make it unconscionable for her to retain it as against the plaintiff. It is in this part of the case that the effective movement of value from the plaintiff to the defendant, without consideration or countervailing advantage, becomes a relevant factor.
54 The principles of equity relevant to this claim are clear. Equity will intervene where an unconscientious use of power is perpetrated by a stronger party upon a weaker. The basic principle was stated in these terms by Fullagar J in Blomley v Ryan (1956) 99 CLR 362:
"The circumstances adversely affecting a party, which may induce a court of equity either to refuse its aid or to set a transaction aside, are of great variety and can hardly be satisfactorily classified. Among them are poverty or need of any kind, sickness, age, sex, infirmity of body or mind, drunkenness, illiteracy or lack of education, lack of assistance or explanation where assistance or explanation is necessary. The common characteristic seems to be that they have the effect of placing one party at a serious disadvantage vis-à-vis the other."
55 Speaking of the jurisdiction of courts of equity to relieve against unconscionable dealing, Deane J made the following observations in Commercial Bank of Australia Ltd v Amadio (1983) 151 CLR 447:
"The jurisdiction is long established as extending generally to circumstances in which (i) a party to a transaction was under a special disability in dealing with the other party with the consequence that there was an absence of any reasonable degree of equality between them and (ii) that disability was sufficiently evident to the stronger party to make it prima facie unfair or "unconscientious" that he procure, or accept, the weaker party's assent to the impugned transaction in the circumstances in which he procured or accepted it. Where such circumstances are shown to have existed, an onus is cast upon the stronger party to show that the transaction was fair, just and reasonable."
56 The relationship between such unconscionable dealing and undue influence was then described by Deane J:
"The equitable principles relating to relief against unconscionable dealing and the principles relating to undue influence are closely related. The two doctrines are, however, distinct. Undue influence, like common law duress, looks to the quality of the consent or assent of the weaker party (see Union Bank of Australia Ltd v Whitelaw [1906] VLR 711, at p.720; Watkins v Combes (1922) 30 CLR 180, at pp.193-194; Morrison v Coast Finance Ltd (1965) 55 DLR (2d) 710, at p.713). Unconscionable dealing looks to the conduct of the stronger party in attempting to enforce, or retain the benefit of, a dealing with a person under a special disability in circumstances where it is not consistent with equity or good conscience that he should do so."
57 The relationship was described in these terms by Brennan J in Louth v Diprose (1992) 175 CLR 621:
"Although the two jurisdictions are distinct, they both depend upon the effect of influence (presumed or actual) improperly brought to bear by one party to a relationship on the mind of the other whereby the other disposes of his property."
58 As Gaudron, Gummow and Kirby JJ emphasised in Bridgewater v Leahy (1998) 194 CLR 457, by reference to a statement of Lord Eldon LC in Huguenin v Baseley (1807) 14 Ves Jun 273, the question is not whether the putative victim knew what he or she was doing, had done or proposed to do, but how the intention was produced.
59 The real point is that equity will neither allow advantage to be taken of a person labouring under a disability nor sanction an overbearing of a vulnerable party's judgment by a stronger party's influence. These forces may be at work even though the person affected becomes a willing participant in a transaction which on its face shows no real sign of unfairness. The equitable wrong lies in the taking of the benefit produced by unconscionable conduct in circumstances where the person engaging in that conduct knows or is to be taken to know of the circumstances of unconscionability.
60 In Turner v Windever [2003] NSWSC 1147, Austin J pointed out that a case of unconscionable dealing involves five elements:
(a) the weaker party must, at the time of entering into the transaction, suffer from a special disadvantage vis-a-vis the stronger party;
(b) the special disadvantage must seriously affect the weaker party's capacity to judge or protect his or her own interests;
(c) the stronger party must know of the special disadvantage (or know of facts which would raise that possibility in the mind of any reasonable person); and
(e) the taking of advantage must have been unconscientious.
61 Austin J added that, once elements (a), (b) and (c) are established, and the improvidence of the transaction is shown, the plaintiff's task is made easier by an equitable presumption to the effect that the improvident transaction was a consequence of the special disadvantage, and that the defendant has unconscientiously taken advantage of the opportunity presented by the disadvantage.
62 The first element referred to by Austin J in Turner v Windever is that, at the time of the transaction, the weaker party suffered from a special disadvantage vis-à-vis the stronger party. In the present case the plaintiff was profoundly deaf. The defendant was not. The plaintiff was entirely reliant upon others to relay to her the content of oral statements made by persons whose manner of speaking did not allow her to lip-read. The defendant was not reliant in this way. The plaintiff had, throughout her marriage of 39 years, relied on her husband to advise and help her with financial and business matters. The defendant was not reliant in this way. The plaintiff's husband was gravely ill and expected to live only a few days. He had told her that the defendant had agreed to look after her. The plaintiff was thus in a state of extreme anxiety and isolation. In these ways, the plaintiff suffered from a special disadvantage vis-à-vis the defendant. The plaintiff had the same kind of emotional dependence on the defendant as was found in Bridgewater v Leahy (above). The defendant said quite clearly in her evidence that 12 January 2004 (the day immediately before the relevant events), "we already knew that my father was not going to be with us for very long; we learned on 9 January that he would only live for three or four days at that stage".
63 The second element is that the special disadvantage seriously affected the weaker party's capacity to judge or protect his or her own interests. In the present case, the plaintiff's isolation from the spoken word, coupled with the absence of both an interpreter and the husband from whom she had for so many years derived support and help, meant that she was, during the meeting of 13 January 2004, not able to judge or protect her own interests. She believed that the defendant - the daughter who had promised to look after her - would see to her interests and was for that additional reason affected in her capacity to protect her own interests.
64 The third element is that the stronger party knew of the special disadvantage or of facts that would raise that possibility in the mind of any reasonable person. In the present case, the defendant was fully and intimately aware of her mother's condition, both physically and emotionally, including by way of reliance on Mr Smith. The defendant knew of her mother's special disadvantage.
65 With the first three elements thus established and the improvidence of the transaction from the plaintiff's viewpoint being manifest, it may be presumed that the improvident transaction was a consequence of the special disadvantage; and that the defendant has unconscientiously take advantage of the opportunity presented by the disadvantage. To that extent, I perhaps need not address those matters. I nevertheless do so.
66 The fourth element is that the stronger party takes advantage of the opportunity presented by the disadvantage. In the present case, the defendant made it her business to pursue a course of obtaining for herself either full ownership of the Wyoming property or, as eventually happened, a one-half interest. She did this in circumstances where she knew that her mother would probably do and sign whatever she asked when they visited the solicitors' office on 13 January 2004. The defendant thus took advantage of the opportunity presented by the plaintiff's disadvantage.
67 The fifth and final element is that the taking of advantage was unconscientious. That element clearly exists in this case. The transaction was, as I have said, an improvident one from the plaintiff's viewpoint. It was, on no view, beneficial to the plaintiff that a one-half share in the Wyoming property should accrue to the defendant through expenditure of funds that were to be received by the plaintiff and Mr Smith but were, in the events that happened, eventually received by the plaintiff alone. The defendant simply appropriated her mother's property. Her beliefs, if they existed, about an agreed gift to her were not consistently held. And she showed, after the event, that she had harboured a resentment towards her parents over a range of matters, including matters to do with money and property she thought they had kept from her. Although she denied it, I am satisfied that the defendant's actions in relation to the acquisition of the Wyoming property were motivated, in part at least, by a belief that her parents' perceived unfair treatment of her justified her taking something from them - in the same way as she later sought to take her father's superannuation as well. The notion that, by taking a half share in the property, the defendant was somehow protecting the plaintiff from her (the plaintiff's) sisters and other relatives is one not supported by any element of the evidence. The plaintiff is seen to have needed protection from her daughter rather than anyone else.
68 The conclusion in the present case must be that the plaintiff's special disadvantage in the course of the meeting on 13 January 2004 made her vulnerable by depriving her of the ability to give a competent and informed consent to the defendant's becoming a co-purchaser and to appreciate where her own interests lay. The defendant knew fully of the limitations and disabilities under which the plaintiff was labouring. The defendant took unconscientious advantage of those limitations and disabilities and is not entitled to rely on any apparent assent of the plaintiff. Equity's intervention against unconscionable dealing will not allow the defendant to retain the interest she obtained by becoming a co-purchaser with the plaintiff under the contract signed on 13 January 2004. The defendant holds that interest upon a constructive trust for the plaintiff.
69 This conclusion makes it unnecessary to consider the third basis on which the plaintiff's case was put, namely, that, in signing the contract as a purchaser in her own right, and not as attorney of Mr Smith, the defendant was in breach of a fiduciary duty owed by her as attorney.
70 It remains to consider the appropriate relief. The plaintiff's first claim is for an order for sale of the Wyoming property under s.66G of the Conveyancing Act. Given the conclusion that the defendant holds her interest as co-owner upon trust for the plaintiff, I do not consider it appropriate to approach the question of relief on the basis that the plaintiff and the defendant are co-owners. My findings mean that the defendant is, in equity, not a co-owner at all. Relief should be framed accordingly.
71 The declaration and orders of the court are as follows: