Mistake

Mistake is the law's most austere response to defective agreement. Misrepresentation, studied last week, normally assumes that a contract has been formed and asks whether one party may rescind because the other made a false statement. Mistake asks a sharper question: was there, despite outward agreement, any contract at all? If the mistake is operative at common law, the contract is void ab initio. No title passes; no contractual obligations arise; third-party rights may collapse. That severity explains the narrowness of the doctrine.

For Tripos purposes, the first task is taxonomic. English law usually distinguishes common mistake, mutual mistake, and unilateral mistake. Common mistake describes both parties sharing the same false assumption: for example, both believe that the subject matter exists. Mutual mistake describes the parties misunderstanding one another, neither necessarily knowing of the other's error: each attaches a different meaning to the apparent agreement. Unilateral mistake describes one party being mistaken and the other knowing, or being treated as knowing, of the mistake. Mistake as to identity is a specialised and difficult form of unilateral mistake, important because it often affects whether an innocent third-party purchaser has acquired title.

The second task is remedial and conceptual. A common-law mistake renders the contract void, not merely voidable. Equity once appeared to offer a more flexible power to set aside a contract valid at law, especially after Solle v Butcher. That route was substantially closed by Great Peace, where the Court of Appeal held that there is no separate equitable jurisdiction to rescind for common mistake merely because performance is less advantageous than expected. Equity remains relevant in adjacent areas, including rectification, non est factum, rescission for misrepresentation, and undue influence, but it is not a general licence to relieve bad bargains.

The third task is to keep mistake separate from construction, implied terms, frustration and misrepresentation. Many apparent mistake cases can be decided more cleanly by asking what the contract, objectively construed, means. Others concern risk allocation: if the contract itself places the risk of the mistaken assumption on one party, mistake cannot contradict that allocation. Where an event occurs after formation, the issue is usually frustration, not mistake. Where one party induced the error by a statement, misrepresentation is ordinarily the natural route.

In a Cambridge supervision or Tripos answer, do not recite categories mechanically. Begin with formation and objective agreement; identify the precise assumption alleged to be false; ask whether the contract allocates the risk; then decide whether the error is sufficiently fundamental to make the agreement void. The best answers treat mistake not as a kindness doctrine but as a structural limit on contractual obligation.

The modern law of mistake was formed by two opposing impulses. One is the will theory: contract depends upon consent, so a profound error may prevent real agreement. The other is objective theory: contractual liability rests upon outward manifestations reasonably understood, not hidden states of mind. English law has overwhelmingly preferred the latter, but has preserved narrow mistake doctrines for cases where the appearance of agreement is too fragile to sustain legal obligation.

Smith v Hughes is the classical starting point. The buyer believed he was purchasing old oats; the seller knew the buyer might be mistaken, but had not promised that the oats were old. The case is often taught as mistake, but its central lesson is objective formation. A party who objectively assents to the other's terms is bound, even if internally mistaken. The law is not concerned with disappointed subjective expectations. It is concerned with whether the words and conduct, assessed reasonably, disclose agreement on the same terms.

Nineteenth-century cases nevertheless accepted that mistake could prevent contract where the error went to the identity or existence of the subject matter. In Couturier v Hastie the parties contracted for corn which had already been sold because it had deteriorated during transit. The House of Lords treated the contract as ineffective, and Parliament later codified a narrow version for specific goods in the Sale of Goods legislation. Mistake as to identity also emerged in the rogue cases. Cundy v Lindsay treated a contract as void where the seller intended to deal only with a reputable firm, Blenkiron & Co, while the rogue impersonated that firm. The result protected the original owner against a third-party purchaser. Later face-to-face cases, especially Phillips v Brooks and Lewis v Averay, pulled in the opposite direction: where the seller deals with the person physically present, the presumption is that he intends to contract with that person, however fraudulent his assumed name may be.

The great constriction of common mistake came in Bell v Lever Bros. Lever Bros paid compensation to terminate two service contracts, not knowing that the employees had already committed breaches justifying dismissal without compensation. The House of Lords held the settlement binding. The mistake did not make the service contracts essentially different from what the parties believed; it merely meant that Lever Bros had made an improvident bargain. Bell is difficult but fundamental. It signals that common mistake is exceptional and that a mistake about legal rights, value, motive, or the commercial wisdom of settlement will usually be insufficient.

The mid-twentieth century briefly promised a more generous equitable doctrine. In Solle v Butcher, Denning LJ suggested that a contract might be valid at law yet voidable in equity where both parties laboured under a fundamental mistake, provided relief could be given on terms. This appealed to judicial conscience and allowed flexible adjustment. But it was doctrinally unstable: if contract law is governed by objective construction and risk allocation, equity should not casually undo valid bargains merely because they rest on erroneous assumptions.

Great Peace restored orthodoxy. The parties contracted to hire a salvage vessel, believing it was much nearer to a distressed ship than it was. The Court of Appeal rejected a separate equitable doctrine of common mistake and affirmed a strict test at common law. The result was not merely historical housekeeping. It aligned mistake with the objective theory of contract and commercial risk. English law now treats mistake as a limited doctrine of formation and fundamental assumption, not as a general jurisdiction to relieve contractual hardship.

1. Mistake begins with objective agreement. The first question is not whether a party was mistaken, but whether the parties objectively agreed. Smith v Hughes remains central. If A offers to sell oats and B accepts, B is not released merely because he hoped the oats were old, unless age was made a contractual term or A's conduct objectively represented that they were old. The same reasoning applies to modern commercial contracts: undisclosed assumptions are not terms.

1. Operative mistake is exceptional because the remedy is usually voidness. A void contract is treated as never having existed. That is why courts resist expanding mistake. In misrepresentation the contract is voidable; rescission may be barred by affirmation, lapse of time, impossibility of restoration or third-party rights. In common-law mistake, by contrast, the supposed contract never transferred title. The doctrine therefore threatens transactional security, particularly where goods have been sold on.

1. Common mistake requires a shared false assumption existing at formation. The false assumption must concern a state of affairs at the time the contract is made. If the relevant event occurs later, the issue is frustration. If parties contract for a ship which both believe exists but which had already sunk, the case is mistake. If the ship sinks after the contract, frustration may arise. The temporal line matters.

1. The mistake must be fundamental. Bell v Lever Bros and Great Peace require more than a mistake as to value, quality, motive or legal advantage. The mistaken assumption must render the subject matter, or the contractual adventure, essentially different from what the parties believed. The formulation is demanding. In Great Peace the vessel was farther away than thought, but still capable of performing the hired function. The contract was bad, not impossible in the relevant sense.

1. The contract must not allocate the risk of the mistake. This is often the decisive point. If a contract says goods are sold as seen, the buyer may bear the risk of defects. If a settlement agreement compromises uncertain claims, each side commonly bears the risk that its legal assessment is wrong. If a guarantee covers the existence of leased equipment, the guarantor may bear the risk that the equipment does not exist, depending on construction. Associated Japanese Bank illustrates the need to construe the contract before invoking mistake.

The cases form a coherent story if arranged around the objective principle and the severity of voidness.

Smith v Hughes supplies the foundation. It is not enough that one party is mistaken about a quality of the goods. Unless the other party has promised that quality, or knowingly allowed the mistaken party to believe that a term was agreed, the outward bargain stands. The decision explains why mistake is not a device for converting motives into conditions.

Couturier v Hastie and the Sale of Goods Act provisions represent the clearest common mistake case: specific subject matter believed to exist did not exist in the relevant sense. This is the easy case because the transaction is deprived of its object from the start. But later authority shows that English law is reluctant to extend the same reasoning to cases where the subject matter exists but is less valuable or less useful.

Bell v Lever Bros is the controlling authority for common mistake. The employer paid compensation to terminate service agreements, unaware that the employees' misconduct would have justified dismissal. The House of Lords refused to set the bargain aside. The settlement was not essentially different; the mistake affected the price worth paying, not the identity of the thing bargained for. Bell is best read as a case about risk in compromise and the insufficiency of mistakes about quality, value and legal advantage.

Associated Japanese Bank v Credit du Nord introduced an influential analytical method. Steyn J asked, in substance, whether the contract on its true construction allocated the risk; only if it did not should common mistake be considered. A guarantee of obligations under a lease of machines was challenged because the machines did not exist. The judgment is valuable not merely for its result but for its method: construction first, mistake second.

Solle v Butcher is important because it is now largely a warning. Denning LJ allowed equitable rescission of a lease where both parties mistakenly believed it was not subject to rent control. The case suggested a softer doctrine: a contract valid at law but voidable in equity on terms. Great Peace rejected that approach for common mistake. In Cambridge essays, Solle should be discussed as an historical episode, not as current general law.

Great Peace is the modern settlement. A salvage company hired a vessel believing it was close to a casualty. It was much farther away, but still capable of rendering some assistance within the contractual framework. The Court of Appeal held there was no operative common mistake and no separate equitable jurisdiction of the Solle kind. The case reasserts strictness, risk allocation, and the need for impossibility or essential difference.

The identity cases are less tidy. Cundy v Lindsay protected the original seller where the rogue impersonated an existing firm in correspondence. Phillips v Brooks and Lewis v Averay favoured third-party purchasers in face-to-face transactions, treating the contract with the rogue as voidable rather than void. Shogun Finance then gave priority to documentary identity in a hire-purchase transaction, holding by majority that the finance company contracted only with the named person in the written document. The result preserves a difficult distinction between written distance dealings and face-to-face dealings. Its practical significance is large; its theoretical elegance is modest.

Saunders v Anglia Building Society completes the picture. The plea of non est factum was confined to cases where the document signed is radically different from what was believed and the signer was not careless. It reinforces the law's general insistence that signatures and outward acts carry responsibility.

See practice questions section below.

See further reading section below.