mistake (defense) | Definition

Doc's CJ Glossary by Adam J. McKee
Course: Introduction / Criminal Law

A mistake defense criminal defense that involves a mistake as to the facts and circumstances surrounding an event can sometimes be a defense to criminal charges; a mistake of law is never an excuse.

In criminal law, a mistake defense is a defense raised by a defendant who claims that he or she made an honest misunderstanding as to a material fact or circumstance surrounding an event. The idea behind the defense is that the defendant did not have the necessary mens rea or criminal intent to commit the crime.

The defense is often raised in cases where a defendant has been charged with a crime that requires a specific intent or knowledge of a particular fact. For example, if a person is charged with embezzlement, which requires the specific intent to steal, the defense may be raised if the defendant can show that he or she honestly believed that the money taken was rightfully theirs.

There are two types of related defenses: mistake of fact and mistake of law. A defense based on an error of fact involves a mistake as to the factual circumstances surrounding the event. In contrast, a mistake of law defense involves a mistake as to the legal consequences of an action.

Under the Model Penal Code, an error of fact can be a defense to a criminal charge if it negates the mens rea required for the offense. For example, if a person is charged with statutory rape and he honestly believed that the victim was of legal age, this misunderstanding of fact could negate the mens rea required for the offense (in rare jurisdictions that don’t disallow the defense by statute).

However, a mistake of law is generally not a defense to a criminal charge. The reasoning behind this is that ignorance of the law is not an excuse. In other words, individuals are expected to know the law, and they cannot claim that they did not know a certain action was illegal.

To raise such a defense successfully, the defendant must be able to show that the error was an honest one and that it was reasonable under the circumstances. If the misunderstanding is found to be reckless or grossly negligent, then it may not be a valid defense.

In addition, some states require that the mistake be a reasonable one, meaning that the mistake must have been one that a reasonable person would have made under similar circumstances.

It is important to note that a mistake defense can be a difficult defense to raise successfully. The prosecution may argue that the defendant did not make an honest mistake or that the mistake was not reasonable under the circumstances.

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Last Modified: 04/10/2023

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