Estoppel is a judicial device in common law legal systems whereby a court may prevent or "estop" a person from making assertions or from going back on his or her word; the person being sanctioned is "estopped". Estoppel may prevent someone from bringing a particular claim. Legal doctrines of estoppel are based in both common law and equity. It is also a concept in international law.
Types of estoppel
There are many different types of estoppel which can arise, but the common thread between them is that a person is restrained from asserting a particular position in law where it would be inequitable to do so. By way of illustration:
If a landlord promises the tenant that he will not exercise his right to terminate a lease, and relying upon that promise the tenant spends money improving the premises, the doctrine of promissory estoppel may prevent the landlord from exercising a right to terminate, even though his promise might not otherwise have been legally binding as a contract. The landlord is precluded from asserting a specific right. If a person brings legal proceedings in one country claiming that a second person negligently injured them and the courts of that country determine that there was no negligence, then under the doctrine of issue estoppel the first person will not normally be able to argue before the courts of another country that the second person was negligent (whether in respect of the same claim or a related claim). The first person is precluded from asserting a specific claim.
Estoppel is an equitable doctrine. Accordingly, any person wishing to assert an estoppel must normally come to the court with "clean hands".
The doctrine of estoppel (which may prevent a party from asserting a right) is often confused with the doctrine of waiver (which relates to relinquishing a right once it has arisen). It also substantially overlaps with, but is distinct from, the equitable doctrine of laches.
Etymology and usage
"Estop" is a verb of Anglo-Norman origin meaning "to seal up" while the noun "estoppel" is based on Old French estoupail (stopper). Where a court finds that a party has done something warranting a form of estoppel, that party is said to be estopped from making certain related arguments or claiming certain related rights. The defendant is estopped from presenting the related defense, or the plaintiff is estopped from making the related argument against the defendant. Lord Coke stated, "It is called an estoppel or conclusion, because a man's own act or acceptance stoppeth or closeth up his mouth to allege or plead the truth."
Overview
Estoppel is sometimes said to be a rule of evidence whereby a person is barred from leading evidence of a fact that has already been settled or they are otherwise precluded from asserting, but that may be an oversimplification. Firstly, although some estoppels relate to preventing a party from asserting facts, others relate to preventing a party from asserting a right or a claim. Secondly, under the conflict of laws in common law jurisdictions, matters of evidence are usually treated as procedural matters for the law of the local court (the ), whereas it is generally accepted that an estoppel may affect substantive rights and are therefore matters to be determined by the proper law (or ) that governs the particular issue.
There are many different types of estoppel that can arise under common law legal systems. It has been judicially noted on more than one occasion that the link between them is often somewhat tenuous. Treitel on Contracts notes that "unconscionability ... provides the link between them", but they nevertheless have "separate requirements and different terrains of application". The courts have long abandoned an attempt to create a single general underlying rationale or principle:
The plea of estoppel is often closely connected with the plea of waiver, the object of both being to ensure bona fides in day-to-day transactions. It is also related to the doctrines of variation and election. It is applied in many areas of contract law, including insurance, banking, and employment. In English law, the concept of legitimate expectation in the realm of administrative law and judicial review is estoppel's counterpart in public law.
Promissory estoppel is often applied where there is a promise or an agreement made without consideration. When used as a defense by a defendant it is sometimes called a "shield", and when used affirmatively by a plaintiff it is sometimes called a "sword". It is most commonly used as a shield, with some commentators stating that it can only be used as a shield, although this varies with jurisdictions.