Mistake Defense in Torts
Mistake is inherently a very vague defense because it centers on the premise that the defendant acted under the mistaken belief his conduct was justified, and that society wants to protect the justification. Mistake should be differentiated from accident: in mistake, the end was sought by the defendant although he did not know it was wrong, in accident the result of the defendant's actions were unintended. One example is that of a police officer acting under what he believes is a valid warrant: since the officer did not legally arrest the plaintiff, he is technically guilty of false imprisonment; but, the action is excused because the officer was acting under mistaken premises.
Mistake inevitably involves the balancing of social policy against the desire to compensate an individual who has been damaged. Mistake will often be a very fact-specific inquiry, where the reasonableness of the defendant's mistaken conclusions, and the particular public policies at issue, are carefully examined. If a defendant has been induced by the plaintiff's own conduct he is usually absolved of all wrong-doing in tort, as long as his reliance on the plaintiff's conduct was reasonable.