Estoppel is a slightly utopian doctrine proposing that any person who asks the courts to enforce a legal remedy should have a clear conscience. Wherever a law is broken, a right of action is created in any person who has suffered a loss (the plaintiff). This right to a remedy is enforced through the courts. In almost all cases, the state of the plaintiff's conscience will be irrelevant to obtaining relief. But, if the plaintiff has said or done something that induced the defendant to change his or her behaviour and that reliance was reasonable, the courts have a discretion to deny the remedy to the plaintiff. Hence, an estoppel is not a legal remedy; rather, it is a remedy availble in common law jurisdictions but applying the maxims of Equity. In the majority of cases, it is only a defence and it works by preventing a plaintiff from enforcing established legal rights, or from relying on a set of facts that would give rise to enforceable rights (e.g. words said or actions performed) if that enforcement or reliance would be unfair to the defendant. Because its effect is to defeat generally enforceable legal rights, the scope of the remedy is often very limited.
In the case of an existing debt, for example, an estoppel could arise where the creditor informs the debtor that the debt is forgiven, but there is no formal termination of the contract. If the creditor later tries to enforce the original contract terms, but the debtor has relied on the representation and has innocently spent the money on something else, the creditor may be estopped from relying on the usual contractual right to repayment because it would be unfair to allow the creditor to change his or her mind. Similarly, a landlord may tell a tenant that the rent is reduced or cancelled for a specific period of time, e.g. "You can pay half rent until the noise and dirt from the maintenance of the common parts is over." If the tenant changes behavior as a result of what is said, the landlord might be "estopped" from retrospectively claiming the full rent.
Estoppel is closely related to the doctrines of waiver, variation, and election and is applied in many areas of law, including insurance, banking, employment, international trade, etc.
English law (see also Estoppel (English law)) defines it as: "a principle of justice and of equity. It comes to this: when a man, by his words or conduct, has led another to believe in a particular state of affairs, he will not be allowed to go back on it when it would be unjust or inequitable for him to so." in Moorgate Mercantile v Twitchings  1 QB 225, CA at 241 per Lord Denning MR.
The definition in American law is similar: "Speaking generally, estoppel is a bar which precludes a person from denying or asserting anything to the contrary of that which has, in contemplation of law, been established as the truth, either by the acts of judicial or legislative officers, or by his own deed, acts, or representations, either express or implied." 28 Am Jur 2d Estoppel and Waiver § 1
The main species of estoppel under English, Australian, and American laws are:
- Estoppel by record This frequently arises as issue/cause of action estoppel, judicial estoppel or res judicata where the orders or judgments made in previous legal proceedings prevent the parties from relitigating the same issues or causes of action,
- Estoppel by deed Where rules of evidence (often regarded as technical or formal estoppels) prevent a litigant from denying the truth of what was said or done, and
- Reliance-based estoppels These are the most important forms. Under English law, this class includes estoppel by representation of fact, promissory estoppel and proprietary estoppel (see Halsbury's Laws of England, Vol 16(2), 2003).
- Estoppel by representation of fact is known as equitable estoppel in American law.
- Equitable estoppel as understood in English law, includes:
- promissory estoppel, and
- proprietary estoppel,
- Although some authorities regard reliance-based estoppels as mere rules of evidence, they are in reality rules of substantive law.
Under English law, estoppel may be:
- by representation of fact, where one person asserts the truth of a set of facts to another;
- promissory estoppel, where one person makes a promise to another, but there is no enforceable contract; and
- proprietary estoppel, where the parties are litigating the title to land.
These are regarded as reliance-based estoppels by Halsbury's Laws of England , Vol 16(2), 2003. Both Halsbury's and Spencer Bower (see below) describe all three estoppels collectively as estoppels by representation . More simply, one party must say or do something and see the other party rely on what is said or done to change behavior. So, suppose that:
- D has the money to repay a debt,
- but the creditor tells D that the debt is forgiven,
- so, without doing anything else, D buys a car that he would not otherwise have been able to afford,
- and the creditor is aware of this reaction.
D is a bare promisee/representee. The original contract is still valid because D has not given any value or consideration to make the termination of liability legally binding. Under normal circumstances, a court will not enforce a bare promise but D may be given a remedy if, and only if, the judge decides that it would be "unconscionable" for the creditor to renege on the promise or represention knowing that D would be penalized. Estoppel is, therefore, an exception to the normal operation of the law and gains its power from equity. Only proprietary estoppel can create a cause of action in English law (and, then, only in very limited circumstances), while the other two can support a defence and a counterclaim. Under Australian law, these estoppels can create both a cause of action and a defense. Under American law, equitable estoppel is available only as a defense, while promissory estoppel can be used as the basis of a cause of action.
To establish a reliance-based estoppel, the victimised party must be able to show both inducement and detrimental reliance, i.e.:
- there must be evidence to show that the representor actually intended the victim to act on the represention or promise, or
- the victim must satisfy the court that it was reasonable for him or her to act on the relevant representation or promise, and
- what the victim did must either have been reasonable, or
- the victim did what the representor intended, and
- the victim would suffer a loss or detriment if the representor was allowed to deny what was said or done - detriment is measured at the time when the representor proposes to deny the representation or withdraw the promise, not at the time when either was made, and
- in all the circumstances, the behavior of the representor is such that it would be "unconscionable" to allow him or her to resile.
Estoppel by representation of fact and promissory estoppel are mutually exclusive: the former is based on a representation of existing fact (or of mixed fact and law), while the latter is based on a promise not to enforce some pre-existing right (i.e. it expresses an intention as to the future). A proprietary estoppel operates only between parties who, at the time of the representation, were in an existing relationship, while this is not a requirement for estoppel by representation of fact.
The test for unconscionability in the English and Australian courts takes many factors into account, including the behavior, state of mind and circumstances of the parties. Generally, the following eight factors are determinative (Michael Spence, Protecting Reliance: The Emergent Doctrine of Equitable Estoppel , Oxford: 1999, pp60-66):
- how the promise/representation and reliance upon it were induced;
- the content of the promise/representation;
- the relative knowledge of the parties;
- the parties' relative interest in the relevant activities in reliance;
- the nature and context of the parties' relationship;
- the parties' relative strength of position;
- the history of the parties' relationship; and
- the steps, if any, taken by the promisor/representor to ensure he has not caused preventable harm.
Estoppel by representation of fact
In English law, estoppel by representation of fact is a term coined by Spencer Bower. This species of estoppel is also referred to as "common law estoppel by representation" in Halsbury's Laws of England , vol 16(2), 2003 reissue.
In The Law relating to Estoppel by Representation , 4th edition, 2004 at para I.2.2, Spencer Bower defines estoppel by representation of fact as follows:
Where one person ('the representor') has made a representation of fact to another person ('the representee') in words or by acts or conduct, or (being under a duty to the representee to speak or act) by silence or inaction, with the intention (actual or presumptive) and with the result of inducing the representee on the faith of such representation to alter his position to his detriment, the representor, in any litigation which may afterwards take place between him and the representee, is estopped, as against the representee, from making, or attempting to establish by evidence, any averment substantially at variance with his former representation, if the representee at the proper time, and in proper manner, objects thereto.
A second definition can be found at Wilken and Villiers, The Law of Waiver, Variation and Estoppel , 2nd ed, Oxford: 2003, at para 9.02:
An estoppel by representation [of fact] will arise between A and B if the following elements are made out. First, A makes a false representation of fact to B or to a group of which B was a member. [It is not necessary to demonstrate A knew that the representation was untrue.] Second, in making the representation, A intended or [in the alternatively,] knew that it was likely to be acted upon. Third, B, believing the representation, acts to its detriment in reliance on the representation. [It must have been reasonable to rely on the representation.] Fourth, A subsequently seeks to deny the truth of the representation. Fifth, no defence to the estoppel can be raised by A.
A representation can be made by words or conduct. Although the representation must be clear and unambiguous, a representation can be inferred from silence where there is a duty to speak or from negligence where a duty of care has arisen. Under English law, estoppel by representation of fact usually acts as a defence, though it may act in support of a cause of action or counterclaim.
Although there is some debate as to whether "unconscionability" is an element that English courts need to take into account when considering estoppel by representation of fact, the Australian courts clearly do (see Wilken and Villiers, para 9-03; The Commonwealth v Verwayen (1990) 170 CLR 394 at 444 per Deane J.)
As noted above, although both English and Australian laws treat promissory and proprietary estoppels as species of equitable estoppel, the status of estoppel by representation of fact is less clear in Australia. The decisions of Waltons Stores (Interstate) v Maher (1988) 164 CLR 387 and Commonwealth v Verwayen (1990) 170 CLR 394, both purport to fuse common law and equitable estoppels into a single unified doctrine, but the New South Wales Court of Appeal in Bryon Shire Council v Vaughan  NSWCA 158 continues to treat estoppel by representation at common law as distinct from equitable estoppel. (See Meagher, Gummow & Lehane's Equity: Doctrines & Remedies , 4th edition, Butterworth: 2002, Chapter 17 and Pakinson, The Principles of Equity , 2nd edition, LBC: 2003, Chapter 7). This can be significant in deciding which court has jurisdiction to adjudicate on the issue.
The American doctrine of equitable estoppel is the same as the English estoppel by representation of fact:
The most comprehensive definition of equitable estoppel or estoppel in pais is that it is the principle by which a party who knows or should know the truth is absolutely precluded, both at law and in equity, from denying, or asserting the contrary of, any material fact which, by his words or conduct, affirmative or negative, intentionally or through culpable negligence, he has induced another, who was excusably ignorant of the true facts and who had a right to rely upon such words or conduct, to believe and act upon them thereby, as a consequence reasonably to be anticipated, changing his position in such a way that he would suffer injury if such denial or contrary assertion was allowed. 28 Am Jur 2d Estoppel and Waiver § 28
The traditional version of proprietary estoppel arises in negotiations affecting title to land. So if:
- one party represents that he or she is transfering an interest in land to another, but what is done has no legal effect, or
- merely promises at some time in the future to transfer land or an interest in land to another, and
- knows that the other party will spend money or otherwise act to his or her detriment in reliance on the supposed or promised transfer,
an estoppel may arise. Thus, in Dillwyn v Llwellyn (1862) 4 De G.F.& J. 517 C.A. a father promised a house to his son who took possession and spent a large sum of money improving the property. The father never actually transfered the house to the son. When his father died, the son claimed to be the equitable owner and the court ordered the testamentary trustees to convey the land to him. See also Inwards v Baker  2 Q.B. 29, C.A.
Although this doctrine was only available in disputes whether directly or indirectly affecting title to real property, it has now gained limited acceptance in other areas of law. The term "proprietary estoppel" is not used in American law, but the principles appear as part of the general doctrine of promissory estoppel.
The doctrine of promissory estoppel prevents one party from withdrawing a promise made to a second party if the latter has relied on that promise and acted upon it.
In English law, a promise made without consideration is generally not enforceable. It is known as a bare or gratuitous promise. Thus, if a car salesman promises not to sell a car over the weekend, but does so, the promise cannot be enforced. But should the car salesman accept even one penny in consideration for the promise, the promise will be binding and enforceable in court. Estoppel is an exceptions to this rule.
The doctrine of promissory estoppel was first developed in Hughes v. Metropolitan Railway Co  but was lost for some time until it was resurrected by Lord Denning in the controversial case of Central London Property Trust Ltd v. High Trees House Ltd  K.B. 130.
In this case, the plaintiffs leased a block of flats to the defendants at an annual rent of £2500. But, because the defendants were unable to find enough tenants while London was being bombed during WWII, they agreed to accept a reduction in rent to £1250. There was no consideration for this promise to accept a lower rent. At the end of the war the flats were again fully let, and the plaintiffs claimed the full rent, plus arrears for the period during the war. Denning J held that, in good conscience, they were only entitled to the full rent from the end of the war and that they were estopped from going back on their promise.
Promissory estoppel requires:
- (i) an unequivocal promise by words or conduct,
- (ii) a change in position of the promisee as a result of the promise (reliance but not necessarily to their detriment ),
- (iii) inequity if the promisor was to go back on the promise.
Estoppel is "a shield not a sword" - it cannot be used as the basis of an action on its own. It also does not extinguish rights. In High Trees the plaintiff company was able to restore payment of full rent from early 1945, and could have restored the full rent at any time after the initial promise was made provided a suitable period of notice had been given.
Estoppel is an equitable (as opposed to common law) construct and its application is therefore discretionary. In the case of D & C Builders v. Rees the courts refused to recognise a promise to accept a part payment of £300 on a debt of £482 on the basis that it was extracted by duress. In Combe v. Combe Denning elaborated on the equitable nature of estoppel by refusing to allow its use as a "sword" by an ex-wife to extract funds from the destitute husband.
Promissory estoppel is not available when one party promises to accept a lesser sum in full payment of a debt, unless the debtor offers payment at an earlier date than was previously agreed. This is the rule formulated in Pinnel's Case (1602) 5 Co Rep 117a, and affirmed in Foakes v. Beer (1884) 9 App Cas 605.
In the many jurisdictions of the United States, promissory estoppel is generally an alternative to consideration as a basis for enforcing a promise. It is also sometimes referred to as detrimental reliance .
The American Law Institute included the principle of estoppel into § 90 of the Restatement of Contracts, stating:
A promise which the promisor should reasonably expect to induce action or forbearance of a definite and substantial character on the part of the promisee and which does induce such action or forbearance is binding if injustice can be avoided only by enforcement of the promise.
The distinction between promissory estoppel and equitable estoppel should be noted:
Equitable estoppel is distinct from promissory estoppel. Promissory estoppel involves a clear and definite promise, while equitable estoppel involves only representations and inducements. The representations at issue in promissory estoppel go to future intent, while equitable estoppel involves statement of past or present fact. It is also said that equitable estoppel lies in tort, while promissory estoppel lies in contract. The major distinction between equitable estoppel and promissory estoppel is that the former is available only as a defense, while promissory estoppel can be used as the basis of a cause of action for damages. 28 Am Jur 2d Estoppel and Waiver § 35
Suppose that B goes to a store and sees a sign that the price of a radio is $10. B tells the shopkeeper that he will get the money and come back later that day to purchase it; there is no discussion of price. The shopkeeper says that when B returns, he will be happy to deal with B as he deals with all his customers but that, if he sells all the radios (he has three), he will not be able to help B. Hearing this, B goes and sells his watch for $10 (it was really worth $15, but since B wanted the money right away, he chose not wait for the best price). When B returns, the sign says $11, and the owner tells B that he has raised the price. In Equity, can you argue that the shopkeeper is estopped by conduct? B relied upon the implied representation that a radio would be sold for $10 when he returned with the money; B has sold his watch at a price lower than the market price, and thus he has acted to his detriment. (Note that if B's watch was worth $10, and he received a fair price, there would be no detriment.) But the problem is that the shopkeeper did not guarantee to hold one of the radios against the possibility of B's return nor did they agree a fixed price. The shopkeeper's conscience might have been affected if he had known that B was going home to collect the money and would definitely return to buy one of the three radios. Indeed, in some common law jurisdictions, a promise by the shopkeeper to hold a specific radio would create a binding contract, even if B had to go for the money. A promise to pay the owner in the future is good consideration if it is made in exchange for a promise to sell a specific radio (one from three is probably sufficiently specific): one promise in exchange for a second promise creates equal value. So the shopkeeper's actual words and knowledge are critical to deciding whether either a contract or an estoppel arises.
For an example of promissory estoppel in the construction industry, suppose that B Ltd consolidates estimates from a number of subcontractors and quotes a single price on a competitive tender. The client accepts B Ltd's quote and construction begins. But one of the subcontractors then claims reimbursement above its original estimate and, because of this change, B Ltd cannot profit from the works. If both parties knew that the accuracy of the individual estimates was critical to the success of the tender and the profitability of the contract as a whole, a court might apply promissory estoppel and allow B Ltd to pay only what the subcontractor originally estimated rather than the new, higher price. But, if both parties hoped that there would be an opportunity to increase the contract prices to reflect additional expenditure, the subcontractor's conscience would not be as limited in seeking a higher payment and B Ltd might be penalised for not building an adequate contingency sum into the tendered price.
One contentious point during the drafting of the Restatement was how to calculate the amount of damages flowing from a promissory estoppel. During the deliberations, the following example was considered: a young man's uncle promises to give him $1,000 to buy a car. The young man buys a car for $500, but the uncle refuses to pay any money. One view was that the young man should be entitled to $1,000 (the amount promised), but many believed that the young man should only be entitled to $500 (the amount he actually lost). The language eventually adopted for the Second Restatement reads: "The remedy granted for breach may be limited as justice requires." - a formula which leaves quantification to the discretion of the court.
Estoppel in pais (literally "by act of notoriety", or "solemn formal act") is the historical root of common law estoppel by representation and equitable estoppel. The terms Estoppel in pais and equitable estoppel are used interchangably in American law.
Estoppel by convention in English law (also known as estoppel by agreement ) occurs where two parties negotiate or operate a contract but make a mistake. If they share an assumption, belief or understanding of how the contract will be interpreted or what the legal effect will be, they are bound by that belief, assumption or understanding if:
- (i) they both knew the other had the same belief, and
- (ii) they both based their subsequent dealings on those beliefs.
Some say that that estoppel by convention is not truly an estoppel in its own right, but merely an instance of reliance-based estoppel ( estoppel by representation would be its most frequent form). Others see it is no more than an application of the rule of interpretation that, where words in a contract are ambiguous, you always interpret those words so as to give effect to the actual intentions of the parties even though that would not be the usual legal outcome.
Estoppel by acquiescence may arise when one person gives a legal warning to another based on some clearly asserted facts or legal principle, and the other does not respond within "a reasonable period of time". By acquiescing , the other person is generally considered to have lost the legal right to assert the contrary.
As an example, suppose that Jill has been storing her car on Jack's land with no contract between them. Jack sends a registered letter to Jill's legal address, stating: "I am no longer willing to allow your car to stay here for free. Please come get your car, or make arrangements to pay me rent for storing it. If you do not do so, within 30 days, I will consider the car abandoned and will claim ownership of it. If you need more time to make arrangements, please contact me within 30 days, and we can work something out." If Jill does not respond, she may be said to have relinquished her ownership of the car, and estoppel by acquiescence may prevent any court from invalidating Jack's actions of registering the car in his name and using it as his own.
Estoppel by deed is a rule of evidence arising from the status of a contract signed under seal - such agreements, called deeds , are more strictly enforced than ordinary contracts and the parties are expected to take greater care to verify the contents before signing them. Hence, once signed, all statements of fact (usually found in the opening recital which sets out the reason(s) for making the deed) are conclusive evidence against the parties who are estopped from asserting otherwise.
Issue Estoppel or ' Res Judicata The civil law use of issue estoppel or res judicata (literally translated as "the fact has been decided") is relatively uncontroversial. It expresses a general public interest that the same issue should not be litigated more than once even when the parties are different. The criminal law application, called double jeodardy provides that a person should not be tried twice for the same offence. In crime/mystery fiction, it is a common plot device to have the villain exploit the rule. In the world of real crime, some cases have achieved notoriety, e.g. in the Birmingham Six saga, the House of Lords ruled in Hunter v. Chief Constable of the West Midlands Police (1982) that issue estoppel applied. Lord Diplock said:
The inherent power which any court of justice must possess to prevent misuse of its procedure in a way which, although not inconsistent with the literal application of its procedural rules, would nevertheless be manifestly unfair to a party to litigation before it, or would otherwise bring the administration of justice into disrepute among right-thinking people.
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