Consideration and promissory estoppel

Consideration is the common law’s principal device for distinguishing enforceable bargains from gratuitous promises. After Weeks 1 and 2, you should already be able to identify an agreement and ask whether it is sufficiently certain and intended to create legal relations. Week 3 adds a further question: even if there is agreement, why should the law enforce this promise? In a contract not made by deed, the orthodox answer is that the promisee must have given consideration.

The doctrine is commonly stated in the language of bargain. A promise is enforceable if it is given in return for something recognised by law as the price of that promise. The price need not be adequate; courts do not ordinarily measure the economic equivalence of the exchange. It must, however, be sufficient: it must be something to which the law can attach value, or at least something requested by the promisor as the agreed exchange. This distinction between adequacy and sufficiency is central, and most first-year mistakes arise from collapsing it.

Promissory estoppel is the corrective counterpart. It developed to prevent a promisor from insisting on strict legal rights where the promisee has relied on a representation that those rights will not be enforced. Its classic form concerns a promise to accept less, or to suspend performance, within an existing legal relationship. It does not normally create a cause of action. It is a shield, not a sword; it prevents enforcement of inconsistent rights where it would be inequitable to allow them to be asserted. Its remedial reach is therefore narrower than contract, though its moral appeal is often stronger.

For Durham Year 1 purposes, the topic is doctrinally foundational. It also tests legal method. You must hold together old common law authorities, modern commercial cases, and equitable reasoning without turning the law into a single vague test of fairness. In problem questions, answer in sequence: agreement; certainty; intention; consideration; then any estoppel answer. In essays, do not merely recite rules. The stronger answer explains why the doctrine survives despite sustained academic criticism: it structures exchange, filters gratuitous undertakings, and protects commercial predictability, but at the cost of artificial reasoning in contract variations and part-payment cases.

The modern doctrine of consideration is the product of assumpsit, not a timeless moral principle. Medieval debt actions enforced certain obligations, especially where a quid pro quo could be shown. Covenant required a deed. The rise of assumpsit allowed courts to enforce undertakings where the defendant had assumed responsibility and the claimant had relied or conferred value. By the nineteenth century, the doctrine had hardened into the requirement that a simple contract must be supported by consideration.

The classic nineteenth-century formulation is associated with Currie v Misa, where consideration was expressed in terms of benefit to one party or detriment to the other. That formulation remains useful, but it can mislead. Consideration is not simply any detriment suffered by the promisee. The detriment must normally be requested as the price of the promise. If I promise you £100 because you have suffered misfortune, your misfortune is not consideration unless it is part of the agreed exchange. The doctrine is therefore better understood as a bargain requirement than as a general benefit-detriment test.

This historical development also explains the sharp distinction between deeds and simple contracts. A promise contained in a deed may bind without consideration because the formality itself substitutes for the bargain requirement. A simple oral or written promise requires consideration unless some other doctrine, such as promissory estoppel, affects enforcement of rights already created.

The nineteenth-century law was especially strict in relation to existing duties and part-payment of debts. Stilk v Myrick treated a promise to pay additional wages for doing what sailors were already contractually bound to do as unsupported by consideration. Foakes v Beer, following Pinnel’s Case, held that part-payment of a debt is not satisfaction of the whole unless accompanied by something legally different. These cases disclose the law’s anxiety about coercion, evidential uncertainty and opportunism. They also show the doctrine’s formalism. A horse, hawk or robe may suffice where a lesser sum alone does not, because the law treats a different kind of performance as capable of forming a new bargain.

The twentieth century softened this rigidity in two ways. First, Williams v Roffey accepted that a practical benefit obtained from securing continued performance may constitute good consideration for a promise to pay more, provided there is no economic duress or fraud. Secondly, promissory estoppel, revived by Denning J in High Trees, restrained promisors from reneging on promises not to enforce strict rights where the promisee had relied. These developments did not abolish consideration. They reconfigured its boundaries. The result is a law of uneasy accommodation: formal doctrine remains, but courts use practical benefit, equitable restraint and duress to manage cases where rigid application would be commercially unrealistic or unjust.

1. Consideration must be sufficient but need not be adequate. The court will not ordinarily inquire whether the bargain was economically wise. A peppercorn may suffice if it is requested as the price of the promise. The law asks whether something recognised as valuable in law was given, not whether the exchange was fair. This protects freedom of contract and avoids turning every bargain into a judicial valuation exercise.

1. Consideration must move from the promisee. The person seeking to enforce the promise must have provided the consideration. This is connected to, but distinct from, privity. At common law, a third party who has not furnished consideration cannot enforce the promise, even if the promise was made for that person’s benefit. The Contracts (Rights of Third Parties) Act 1999 modifies privity in defined circumstances, but it does not abolish consideration as between contracting parties.

1. Past consideration is not good consideration. An act performed before the promise is made is not normally the price of that later promise. If A rescues B’s property and B later promises payment, the rescue was not given in exchange for the promise. The main qualification is the doctrine in Lampleigh v Braithwait and Pao On: where the act was done at the promisor’s request, both parties understood it was to be remunerated, and payment would have been legally enforceable had it been promised in advance, a later promise may fix the amount or evidence the earlier bargain.

1. Performance of an existing public duty is not generally good consideration. If a person merely does what the law already requires, there is no fresh price for the promise. But performance exceeding the public duty may suffice. The line is fact-sensitive: police attendance under ordinary duty differs from special services requested by a private organiser.

The case law is best organised around four questions: what counts as value, when an existing duty can count, what happens when a creditor accepts less, and when equity restrains reliance on strict rights.

Currie v Misa supplies the traditional benefit-detriment formula. Its importance lies not in making detriment alone sufficient, but in identifying consideration as something legally recognised as value. The better modern account reads Currie through the bargain principle: the benefit or detriment must be part of the agreed exchange.

Stilk v Myrick represents the strict existing-duty rule. Sailors who promised to complete the voyage after desertions could not enforce a promise of extra wages because they were already bound to use their efforts in emergencies of the voyage. The decision is often contrasted with Hartley v Ponsonby, where the remaining crew were asked to undertake a substantially more dangerous voyage after desertions; that additional risk could constitute consideration. The distinction is not always tidy, but it demonstrates the law’s concern to separate mere performance of an existing obligation from fresh undertaking.

Pinnel’s Case and Foakes v Beer form the spine of the part-payment rule. Payment of £500 cannot discharge a debt of £1,000 merely because the creditor promised to accept it. The debtor gives no fresh consideration. The rule is commercially inconvenient but doctrinally entrenched. Its survival after Williams v Roffey remains a major point of controversy.

Williams v Roffey is the modern turning point for promises to pay more. The Court of Appeal treated practical benefit as capable of amounting to consideration where the promisor obtains commercial advantages from the promisee’s continued performance and the promise is not extracted by duress. It narrows Stilk without expressly overruling it. The result is a functional, commercially realistic doctrine, but one that generates tension with Foakes.

High Trees revived promissory estoppel in its modern contractual form. A landlord who promised reduced rent during wartime conditions could not claim the forgone balance for that period. The promise operated because it was intended to be acted upon and was acted upon. Yet the decision did not enforce a freestanding promise; it restrained strict legal rights arising under an existing lease.

Combe v Combe then confined the doctrine. A wife could not use estoppel to enforce her husband’s promise of maintenance where there was no consideration. Denning LJ insisted that estoppel could not abolish consideration by indirection. D & C Builders v Rees added that equity will not assist a party who has procured a concession inequitably. MWB brings the modern law full circle: the Supreme Court upheld no oral modification clauses and avoided finally deciding whether practical benefit can support a promise to accept less. That avoidance is itself exam-relevant. The law is unsettled at the point where practical benefit, debt variation and estoppel intersect.

See practice questions section below.

See further reading section below.