Study guide
2.5 Mistake in Contract Formation
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1 Introduction & FYLSE Examination Guide
1.1 FYLSE Exam Structure, Passing Standard & Administration 1.2 Study Method, Pacing & MBE-Style Technique
2 Contracts: Mutual Assent, Capacity & Contract Formation
2.1 The Offer & Objective Theory of Assent 2.2 Termination & Irrevocability of Offers 2.3 Acceptance & the Mailbox Rule 2.4 Mirror Image Rule & UCC 2-207 Battle of the Forms 2.5 Mistake in Contract Formation 2.6 Fraud, Duress, Undue Influence & Illegality 2.7 Capacity to Contract
3 Contracts: Consideration, Estoppel & Implied Obligations
3.1 Consideration & the Bargained-For Exchange 3.2 Past & Moral Consideration, Pre-Existing Duty & Modification 3.3 Promissory Estoppel & Detrimental Reliance 3.4 Implied-in-Fact Contracts & Quasi-Contract 3.5 Implied Covenant of Good Faith, Fair Dealing & Indefinite Terms
4 Contracts: Third-Party Beneficiaries, Assignment & Delegation
4.1 Third-Party Beneficiary Contracts 4.2 Assignment of Rights 4.3 Delegation of Duties
5 Contracts: Statute of Frauds, Parol Evidence & Interpretation
5.1 Statute of Frauds: Contracts Within the Statute 5.2 Satisfying the Statute: Writing, Signature & Exceptions 5.3 The Parol Evidence Rule 5.4 Contract Interpretation & Canons of Construction
6 Contracts: Performance, Conditions, UCC Warranties & Breach
6.1 Conditions: Express, Constructive & Excuse 6.2 Substantial Performance vs. Perfect Tender 6.3 Cure, Rejection, Revocation & Installment Contracts 6.4 UCC Article 2 Warranties & Risk of Loss 6.5 Anticipatory Repudiation & Insecurity
7 Contracts: Remedies, Discharge & Changed Circumstances
7.1 Expectation Damages & Their Limitations 7.2 Reliance, Restitution & Liquidated Damages 7.3 Specific Performance & Injunctive Relief 7.4 UCC Article 2 Buyer's and Seller's Remedies 7.5 Impossibility, Impracticability & Frustration of Purpose 7.6 Discharge by Agreement: Rescission, Novation & Accord and Satisfaction
8 Criminal Law: Principles of Criminal Liability & Mens Rea
8.1 Actus Reus, Voluntary Acts & Omissions 8.2 Criminal Causation & Intervening Causes 8.3 Common Law & Model Penal Code Mens Rea 8.4 Mistake of Fact, Mistake of Law & Concurrence
9 Criminal Law: Inchoate Offenses & Accomplice Liability
9.1 Criminal Attempt & Impossibility 9.2 Solicitation & the Merger Doctrine 9.3 Conspiracy & Merger Doctrine 9.4 Accomplice Liability: Actus Reus & Mens Rea 9.5 Scope of Accomplice Liability, Withdrawal & Parties to Crime
10 Criminal Law: Homicide & Crimes Against the Person
10.1 Common Law Murder & Malice Aforethought 10.2 Degrees of Murder, Premeditation & Deliberation 10.3 The Felony Murder Rule & Its Limitations 10.4 Voluntary & Involuntary Manslaughter 10.5 Non-Homicide Crimes Against the Person
11 Criminal Law: Property Crimes, Theft & Habitation
11.1 Common Law Larceny 11.2 Embezzlement & False Pretenses 11.3 Robbery & Extortion 11.4 Receiving Stolen Property 11.5 Burglary 11.6 Arson
12 Criminal Law: Defenses: Capacity, Justification & Excuse
12.1 Insanity: The Four Legal Tests 12.2 Intoxication, Diminished Capacity & Infancy 12.3 Self-Defense & Defense of Others 12.4 Defense of Property, Habitation & Law Enforcement Privileges 12.5 Duress & Necessity 12.6 Entrapment & Mistake as an Excuse
13 Torts: Intentional Torts to Persons & Property
13.1 Intent, Motive & Incapacity in Intentional Torts 13.2 Transferred Intent 13.3 Battery & Assault 13.4 False Imprisonment 13.5 Trespass to Land 13.6 Trespass to Chattels & Conversion
14 Torts: Privileges & Defenses to Intentional Torts
14.1 Consent: Express, Implied & Capacity 14.2 Exceeding & Vitiating Consent 14.3 Self-Defense & Defense of Others (Tort) 14.4 Defense of Property & Recapture of Chattels 14.5 Public & Private Necessity 14.6 The Shopkeeper's Privilege
15 Torts: Negligence — Duty of Care & Breach
15.1 Duty of Care & the Foreseeable Plaintiff 15.2 Affirmative Duties to Act & Special Relationships 15.3 Standard of Care: The Reasonable Person & Children 15.4 Professional Negligence, Informed Consent & Negligence Per Se 15.5 Land Possessor Liability & Premises Duties 15.6 Breach of Duty & Res Ipsa Loquitur
16 Torts: Causation, Defenses, Multiple Tortfeasors, Wrongful Death & Damages
16.1 Cause in Fact & Multiple Actors 16.2 Proximate Cause & Intervening Forces 16.3 Contributory, Comparative Negligence & Assumption of Risk 16.4 Joint and Several Liability, Contribution & Indemnity 16.5 Vicarious Liability & Non-Delegable Duties 16.6 Wrongful Death & Survival Actions 16.7 Statute of Limitations & Claim Accrual 16.8 Tort Damages: Compensatory, Nominal, Punitive & Mitigation
17 Torts: Strict Liability & Products Liability
17.1 Strict Liability for Animals 17.2 Abnormally Dangerous Activities & Scope of Risk 17.3 Strict Products Liability & Defect Categories 17.4 Products Liability Under Negligence, Warranty & Misrepresentation 17.5 Defenses to Products Liability
18 Torts: Emotional Distress, Defamation, Privacy & Economic Torts
18.1 Intentional Infliction of Emotional Distress 18.2 Negligent Infliction of Emotional Distress 18.3 Common Law Defamation: Elements, Libel & Slander 18.4 Constitutional Limits, Privileges & Defenses to Defamation 18.5 Invasion of Privacy 18.6 Nuisance & Economic Torts
2.5 Mistake in Contract Formation
Key Takeaways Explain This Topic AI
Mutual mistake makes a contract voidable by the adversely affected party where both parties erred about a basic assumption that materially affects the exchange and that party did not bear the risk.
Unilateral mistake is generally not a defense unless the other party knew or had reason to know of the error, or enforcement would be unconscionable.
A party bears the risk of mistake when the agreement assigns it, when the party proceeds with conscious awareness of limited knowledge, or when a court allocates it as reasonable.
Mistakes in judgment about value are not mistakes of fact and do not excuse performance.
Last updated: September 2026
Mistake in Contract Formation
Even where the outward mechanics of offer and acceptance appear satisfied, a contract may be unenforceable if genuine mutual assent was defective. This section analyzes the primary formation defenses: mutual and unilateral mistake, fraud and misrepresentation, physical and economic duress, undue influence, and agreements void for illegality or unconscionability.
I. Mistake Doctrine: Mutual vs. Unilateral
A legal mistake is an erroneous belief not in accord with the facts at the time the contract was executed (Restatement (Second) of Contracts § 151). A mistaken prediction regarding future events is not a mistake; it is evaluated under the doctrine of impracticability or frustration of purpose.
Mutual Mistake (Restatement § 152)
Where both parties share a mistaken belief at the time of contract formation, the contract is voidable by the adversely affected party if three elements are satisfied:
Basic Assumption : The mistake relates to a basic assumption on which the contract was made (e.g., the identity, existence, or core physical nature of the subject matter);
Material Effect : The mistake has a material adverse effect on the agreed exchange of performances (rendering the transaction substantially different from what was contemplated); AND
No Assumption of Risk : The adversely affected party did not bear the risk of the mistake under the rules stated in Restatement § 154.
Allocation of Risk (Restatement (Second) § 154)
A party bears the risk of a mistake when:
Allocated by Agreement : The contract assigns the risk to that party (e.g., an explicit "as is" clause or disclaimer);
Conscious Ignorance (Restatement § 154(b)) : The party is aware at the time of contracting that they have only limited knowledge regarding the facts to which the mistake relates, but treats that limited knowledge as sufficient (e.g., selling an unknown stone or uncut mineral for $10 without an appraisal; the seller assumes the risk of its true identity and value);
Allocated by Court : The court allocates the risk to that party on the ground that it is reasonable under the circumstances.
Seminal Precedents on Mistake:
Raffles v. Wichelhaus (The Peerless ): Mutual misunderstanding of an ambiguous material term (two ships named Peerless sailing from Bombay in different months). Where neither party knows or has reason to know of the ambiguity, or where both know, no mutual assent exists and no contract is formed.
Sherwood v. Walker (Rose 2d of Aberlone): Mutual mistake as to the barrenness of a pedigreed cow. Because a breeding cow was a substantially different creature than a beef cow, the mistake went to the whole substance of the agreement, rendering it voidable.
Unilateral Mistake (Restatement § 153)
Where only one party is mistaken as to a basic assumption, the contract is generally enforceable . A unilateral mistake renders the contract voidable by the mistaken party only if the mistaken party did not bear the risk of the mistake, AND:
The non-mistaken party knew or had reason to know of the mistake , or the non-mistaken party's fault caused the mistake (e.g., "snapping up" a subcontractor bid that is 60% lower than all competing bids due to an obvious transposition error); OR
The effect of the mistake is such that enforcement of the contract would be unconscionable (severe, oppressive hardship), and the non-mistaken party has not substantially changed position in reliance.
III. Mistakes That Do Not Excuse
Not every error is a legally operative mistake, and most wrong answers in this area rely on the distinction.
Situation Operative mistake? Reason
Error about the market value of the subject matter No Value is a matter of judgment and opinion, not an existing fact. Each party assumes the risk of a bad bargain.
Error about future events or profitability No A mistake must concern a fact existing at the time of contracting.
Conscious ignorance — a party knows their knowledge is limited and proceeds anyway No The party has consciously assumed the risk under Restatement § 154(b).
Error induced by the party's own negligence in reading the contract Generally no The duty to read is enforced unless the other party knew of the error.
Scrivener's error — the writing fails to record the agreement the parties actually reached Not voidable, but reformable The remedy is reformation to conform the writing to the true agreement, not rescission.
The distinction between a mistake of fact and a mistake of value does the heaviest work. In the classic barren-cow problem the mistake was operative because the parties were wrong about the animal's capacity to breed , an existing physical fact. Had they simply misjudged what a breeding cow was worth, no relief would follow.
IV. Remedies
Rescission unwinds the contract and returns the parties to their pre-contract positions, with restitution of benefits conferred.
Reformation rewrites the instrument to reflect the actual agreement, and is the exclusive remedy for a scrivener's error or a mistake in transcription.
A court sitting in equity may also impose conditions on rescission, requiring the avoiding party to compensate the other for reliance expenditures where that is necessary to avoid injustice.
V. FYLSX Application Pattern
Mistake questions almost always follow one of three shapes:
The mispriced bid. A subcontractor's bid is dramatically below every competing bid because of an arithmetic slip, and the general contractor snaps it up. This is unilateral mistake, and the general contractor's reason to know of the error makes the bid voidable. Watch for the variant where the general contractor had already relied on the bid in its own successful tender — some courts then deny rescission.
The shared factual assumption. Both parties transact over a thing that turns out to be materially different from what they assumed — an unsigned painting believed authentic, land believed buildable. This is mutual mistake, voidable at the option of the adversely affected party unless that party bore the risk.
The ambiguity that defeats assent. Neither party knows the term has two meanings, and each attaches a different one. This is not really a mistake defense at all but a failure of mutual assent, and no contract forms in the first place.