Can Mistake of Fact or Mistake of Law Be a Defense?

Mistake of fact and mistake of law are legal defenses that a defendant might raise to dispute criminal charges. A mistake of fact happens when someone is wrong about a factual circumstance, such as who owns property or what an object is. Mistake of law refers to a misunderstanding of how a law works or belief that something is legal when it's not. Whether either defense might apply depends on the elements of a crime, what state of mind must be proven, the circumstances of the mistake, and law in that state.

Can Mistake of Fact Be a Defense to Criminal Charges?

A mistake of fact can be a defense when it negates a mental state required to establish an element of a crime. Criminal statutes often require a prosecutor to prove that a defendant acted intentionally or knowingly. A factual mistake may show that the defendant didn't act with that specific intent.

Suppose John tells Marlene she can borrow his lawnmower, but he accidentally gives her the wrong address. Marlene heads to the address John gave her and sees a lawnmower in the front yard. She loads it up on her trailer just as the homeowner pulls up the driveway and calls the police. The police arrest her for theft.

In this situation, Marlene’s mistake would likely clear her from theft charges. To commit theft, a person must take another’s property with the intent of permanently depriving the owner of their property. Marlene didn't take the lawnmower with the intent to steal it from the homeowner. She reasonably relied on the information John gave her. Without that specific intent, she didn’t commit theft.

Does the Mistake of Fact Have to Be Reasonable?

It depends on the crime and the jurisdiction. Some states require a person's mistake of fact to be both honest and reasonable. Let’s say John invites Marlene over for an open house. He gives her the correct address and says to look for the yellow house. Marlene drives down the street, pulls up to the first yellow house she sees, and walks in. The alarm goes off and police arrive minutes later. They arrest her for trespassing. Marlene probably won’t get out of these charges because her mistake wasn’t reasonable. She had the correct address and didn’t bother to look at it.

Other times, an honest mistake of fact may suffice to defend against charges, even if the mistake wasn't reasonable. Suppose Marlene sees an old, rusty motorcycle leaning up against a fence. Grass is growing around it and she thinks it's abandoned. But the fence belongs to a known chop shop. While her mistaken belief that the motorcycle was abandoned was honest, the average person would have likely known it was likely stolen. Regardless, she might have a defense for receiving stolen property in some states, because she honestly believed the motorcycle was abandoned and not stolen. 

Can a Defendant Use Mistake of Fact Against a Strict Liability Crime?

Not usually. Mistake of fact doesn’t generally absolve a person from criminal liability for strict liability crimes, such as statutory rape or speed limit laws. Strict liability crimes don’t require that a defendant acted with any specific knowledge or intent. In other words, mistake of fact is irrelevant. For instance, a person commits statutory rape by having sexual intercourse with a child under the age of consent. It doesn’t matter if the defendant believed the child to be older. Similarly, a person who drives over the speed limit without realizing it won't avoid a speeding ticket.

Can Mistake of Law Be a Defense?

As a general rule, no. Mistake of law is rarely a defense. A mistake of law means a person misunderstood a law or didn’t know it existed. To allow a mistake of law to be a defense would be to encourage people to stay ignorant or claim ignorance of the law. It would invite people to justify wrongful acts based on their interpretation of what the law meant to them. In other words, the laws would lose their certainty and enforceability.

The General Rule

Suppose Casey, a long-time resident of Colorado and regular pot smoker, moves to a new state. He brings his recreational weed with him, assuming recreational weed is legal in every state. Casey was wrong and, within a week, he was in jail on marijuana possession charges. Although Casey didn't intentionally break the law, he doesn't have a legitimate defense based on his mistaken belief that recreational marijuana use was legal in every state.

What if Casey had tried to look up the marijuana laws in his new state and misunderstood the legal difference between medical and recreational marijuana? Medical marijuana is legal (with a prescription) but recreational marijuana is not. Would this mistake of law be a defense? Again, no. Reliance on one’s own interpretation of the law won’t get you off the hook. Even if Casey had contacted an attorney who gave bad and incorrect advice, reliance on the attorney's opinion still wouldn’t be a defense.

Limited Circumstances

In very limited circumstances, mistake of law can be a defense.

Let’s say Casey’s new state of residence made recreational weed legal, but the law was challenged. While the law goes through the courts, the state’s attorney general incorrectly puts out an opinion stating that weed is still legal pending the court’s decision. If Casey relied on this government interpretation, he might be able to raise a mistake of law defense if he’s charged with illegal possession.

Another situation where mistake of law might be a defense is when the criminal statute requires proof the defendant knowingly violated a legal duty or law. For example, in certain federal tax-crime cases, the government must prove the defendant acted willfully to disobey a known legal duty. This willfulness requirement protects the average person from being prosecuted for mistakes made due to the complexity of the tax laws.

Talk to a Lawyer

As noted above, the differences between mistake of fact and law can be difficult to ascertain. To add to the confusion, every state has different laws and court interpretations of those laws. One state might make an exception to the general rules noted above. For instance, some states allow a mistake of fact defense in certain statutory rape cases (but not in all cases). If you face criminal charges, contact a criminal defense attorney or ask the court for a public defender to help you understand the laws and navigate the criminal legal system.