Mistake of Fact Law and Legal Definition
The law distinguishes between mistakes of law and mistakes of fact in various contexts, such as contracts, appeals, and criminal defenses. Some cases involve parties to a contract seeking to have a court declare a contract void due to a mistake of fact. In contract law, a mistaken understanding of the law (as distinguished from facts) by one party only is usually no basis for rescission of a contract since "ignorance of the law is no excuse." Where only one of the parties is mistaken about facts relating to the contract, the mistake will not prevent formation of a contract unless the nonmistaken party is or should have been aware of the mistake made by the other party, or if the mistake was due to mathematical mistake in addition, summation, subtraction, division, or multiplication and was made inadvertently and without gross negligence.
When both parties make a mistake of fact about something going to the heart of the bargain, the contract is void. Generally, a mistake of value is not a defense, and the contract is valid, unless the mistaken value is due to a mistake of material fact.
The earlier version of the Restatement of Restitution provided that "a person who, induced thereto solely by a mistake of law, has conferred a benefit upon another to satisfy in whole or in part an honest claim of the other to the performance given, is not entitled to restitution."
A more modern draft of the Restatement (Third) of Restitution and Unjust Enrichment provides that, "Payment of money resulting from a mistake by the payor as to the existence or extent of the payor's obligation to an intended recipient gives the payor a claim in restitution against the recipient to the extent the payment was not due."
In appellate review of lower court decisions, such review is generally limited to reviewing mistakes of law and the factual findings of the lower court won't be disturbed. The appellate court will only seek to determine if the law relied upon was interpreted and applied correctly in the lower court.
A mistake of fact is sometimes raised as a defense in criminal cases. For example, in an attempted murder, a defendant might claim that although they pulled the trigger of the gun, they made a mistake in thinking the gun was loaded, when in fact it wasn't. However, such a defense doesn't prevent the trier of fact from finding they had the necessary elements needed to prove the crime, since the criminal intent to kill was nevertheless present. However, if one is charged with stealing based upon taking another person's hat from a hatrack when they intended to take their own, this may be found to lack the criminal intent necessary to convict for theft.