Mistake of Law

The defense of mistake of law raises two issues. The first issue occurs where, because of a mistake of law, the defendant did not have the requisite intent to commit a crime. The second issue occurs where, because of a mistake of law, the defendant did not know that an act that he committed intentionally was criminal. It is important to understand the distinction between these two issues because, while mistake of law will usually be allowed as a valid defense in the former situation, it will generally not be allowed in the latter situation.

As we just mentioned, a defendant can use a mistake of law defense to show that he did not have the requisite intent to commit a crime. In such an instance, if the prosecution cannot prove beyond a reasonable doubt that the defendant did have the requisite intent, the defendant must be acquitted. See Cheek v. United States, 498 U.S. 192 (1991). For example:

Brian has lost his cat Fudgy. A few days later, Jacob finds Fudgy. Jacob knows that Fudgy belongs to Brian. Jacob places an ad in the newspaper and posts signs up around the neighborhood advertising that he has found a cat fitting Fudgy’s description. Jacob honestly but mistakenly believes that if no one responds to the ad within fifteen days, he will acquire title to the cat. In this case, even though Jacob was mistaken only as to the law and even though he knew who Fudgy’s owner was, Jacob will not be guilty of the crime of larceny because larceny requires an intent to permanently deprive another person of his property. Here, because of a mistake concerning the law, Jacob believed that the cat was his. Therefore, he lacked the necessary intent to deprive Brian of his property and he thus cannot be convicted of larceny.

Please note that to the extent that a defendant can use a mistake of law defense (to negate a law's requisite intent element), it applies even if the mistake he made was unreasonable.

Generally, if a defendant had the requisite intent to commit an act but, because of a mistake of law, he did not know that his act was illegal, he will not have a valid defense. This is the basis for the popular maxim "Ignorance of the law is no excuse." For example:

Brian is walking down the street one day when he passes Jacob’s house and happens to see his lost cat, Fudgy, sitting in the living room window. Brian goes over to the window, forces it open, reaches inside, and takes Fudgy out. The common law definition of burglary is the breaking and entering into the dwelling of another with the intent to commit a felony. Further, in the state where Brian lives, it is considered a crime to remove any item from another person’s house without the person’s consent, whether that item belongs to them or not. In this case, Brian has broken and entered Jacob’s house and he did so with the intent of removing an item without Jacob’s consent. Therefore, Brian has committed a burglary. If Brian tries to argue that he did not know that he was not allowed to take his own property from someone else’s house without the house owner's consent, Brian will still be convicted. In this case, Brian’s defense does not demonstrate that he lacked the intent to commit the crime. Brian had every intention of removing Fudgy from Jacob’s house. Rather, all this defense demonstrates is that Brian was ignorant of the law and ignorance of the law will not serve as a valid defense.

Although the general rule is that mistake of law is no defense, there are situations in which certain jurisdictions allow a defense of mistake of law. Common to all these situations is that the defendant’s mistake of law must be reasonable.

The first situation in which mistake of law can be a valid defense is where the defendant relied on a statute that was later found to be unconstitutional. If a defendant relied in good faith on a statute that made his conduct permissible and that statute is later found to be unconstitutional, he can use mistake of law as a successful defense. For example:

The state of North Carolina passes a law allowing police officers to shoot traffic offenders on sight. Officer Barney Fife sees Andy driving 56 miles per hour in a 55 MPH zone and promptly blows Andy's brains out. The following month, the federal court for the district of North Carolina rules the statute unconstitutional, saying that it deprives North Carolina citizens of their right to life. Officer Fife's actions were in good faith reliance of the law and he therefore cannot be charged with murder.

The second basis for using this defense is where the defendant relied in good faith on a judicial opinion that said that his conduct was legal. For example:

A month after the previous example, the Court of Appeals for the Eleventh Circuit overrules the North Carolina Court's ruling and reinstates the statute. The next day, Officer Fife sees Aunt Bee commit a traffic violation when she does not come to a complete stop at a stop sign. Barney promptly blows her head off. The following month, the U.S. Supreme Court overrules the Court of Appeals and rules the statute unconstitutional after all. Once against, Fife has a valid defense of mistake of law.

The third basis for which the defendant can use this mistake of law defense is where he relies on an interpretation of the law given by either a person or an agency that is responsible for administering or enforcing the law. For example:

Brian is walking down the street one day when he sees his lost cat Fudgy sitting in Jacob’s living room window. Brian pulls out his cell phone, calls his uncle, the Chief Justice of the State Supreme Court, and asks if it is legal for him to enter Jacob’s house to get Fudgy. Brian’s uncle tells him that it is legal and Brian enters Jacob’s house and takes Fudgy out. If Brian’s uncle is wrong so that Brian was not, in fact, allowed to enter Jacob’s house, Brian can successfully defend himself using the mistake of law defense, because he relied in good faith on an interpretation of the law given by a person who is responsible for administering the law.

Please note that all jurisdictions agree that good faith reliance on the advice of a private attorney is not enough for a mistake of law defense to be valid. See State v. Downs, 21 S.E. 689 (N.C. 1895).

Finally, it is important to note that some crimes require knowledge of the law as an element of the crime itself (such as tax evasion, which requires knowledge that taxes were due for the crime to have been committed). In such cases, a mistake of law, even an unreasonable one, will serve as a valid defense.