An affirmative defense that alleges that an act was not criminal because the defendant did not know the act was prohibited. See also Mistake of Fact and Mistake of Law.

a belief not in accord with the facts

a fact that most dancers would stand by

a mismatch of plan or subgoal with the main goal, which may occur either because of lack of knowledge of the situation, erroneous knowledge, or faulty reasoning

an erroneous belief related to the facts as they exist at the time the contract is made

a very poor excuse and it smells real fishy

Refers to a belief of the contracting parties that is not in accord with existing facts. It is also a legal defense used in certain circumstances when a defendant may negate the required element of criminal intent. For example, a person who mistakenly takes another person's coat, believing it to be his or her own, will not be guilty of theft.

a fundamental mistake can void the whole contract. The mistake can be common to both parties eg they think they are buying and selling a car, which has been destroyed and neither is yet aware of this. Alternatively the mistake can be mutual eg where they are in fact thinking of entirely different cars but don't realise it. Lastly there can be a unilateral mistake where one party is mistaken and the other party knows they are but this can cross over into misrepresentation or even fraud.

Unlike mistake of law, which is not usually a defense, mistake of fact may sometimes offer exculpation (as in excuse) by allowing a criminal defendant some relief from liability for having broken the law.