Unilateral Mistake Defense

Unilateral mistake permits avoidance when the other party knew or caused the mistake.

Representative cases

• Rulli v. Fan Co. 79 Ohio St. 3d 374 · Ohio Supreme Court
• Home Savers, Inc. v. United Security Co. 741 P.2d 1355 · Nevada Supreme Court
• Thompson v. AIG Hawaii Ins. Co., Inc. 142 P.3d 277 · Hawaii Supreme Court

Related Defenses to Formation rules

• Capacity to ContractMinors, mentally incompetent persons, and intoxicated individuals may avoid contracts due to lack of capacity.
• Misrepresentation DefenseContracts induced by material misrepresentation are voidable when justifiably relied upon.
• Fraud DefenseFraudulent inducement renders a contract voidable; fraud in factum may render it void.
• Duress DefenseDuress exists when an improper threat leaves no reasonable alternative.
• Undue Influence DefenseUndue influence arises from unfair persuasion of a vulnerable party by someone in a dominating position.
• Mutual Mistake DefenseA contract is voidable when both parties are mistaken about a basic assumption materially affecting the exchange.
• UnconscionabilityA court may refuse enforcement of unconscionable terms based on unfair surprise or oppressive results.
• Statute of Frauds CategoriesThe SOF applies to marriage, year-or-more, land, executors, goods ≥ $500, and suretyship.

Part of Contracts on Core Legal Rules — foundational MBE-tested principles with primary-source citations.