Mistakes of Law by Criminal Defendants

Posted by Sample HubSpot User on Wed, Aug 10, 2016 @ 10:59 AM

There’s some truth to the saying that “ignorance of the law is no defense.”

A longstanding rule in criminal law is that a “mistake of fact” is a valid defense, whereas a “mistake of law” is not. But the waters are very murky in this area of law. There are many exceptions to the general rule, and the difference between mistakes of fact and law isn’t always clear.

(For more on the difference between these kinds of mistakes, see Is “mistake of fact” a defense to criminal charges?)

Mistakes and Ignorance

Mistake of law is often referred to as “ignorance of the law.” A typical mistake-of-law scenario involves a person admitting to committing an illegal act, then claiming he didn’t know the act was illegal.

Under the general rule, a person accused of a crime cannot dodge responsibility by claiming he didn’t know the act was illegal. Put another way, courts presume that everyone knows the law, meaning that ignorance of the law is rarely a valid defense to a criminal charge. (See Can I be convicted of a crime if I didn’t realize what I did was illegal?)

Example: Bernard recently moved to Texas from Amsterdam. He was arrested while smoking a marijuana cigarette in downtown Houston. He admits to smoking marijuana, but argues that he had no idea marijuana was illegal in Texas. Bernard’s ignorance of the law isn’t a legitimate defense.

Mistake-of-Law Exceptions

There are a handful of generally recognized exceptions that allow criminal defendants to claim mistake of law as a valid defense. But where these exceptions apply, courts generally consider mistake of law an affirmative defense—the person accused of the crime must present evidence that raises or proves the defense.

Specific Intent

Mistake of law can be a defense where the defendant’s misunderstanding negates a specific intent that is a required element of the offense. Some courts limit this specific intent exception to situations involving ignorance of non-penal (non-criminal) laws, such as the tax code.

For example, mistake of law is a defense to the federal crime of willfully filing a false income tax return. A violation of that law requires proof that the person had the specific intent to violate the tax code when she filed her tax return. As such, ignorance of the law can be a defense. So, for example, someone who files an income tax return that turns out to be false due to a misunderstanding of the reporting requirements may have a defense. (United States v. Pomponio, 429 U.S. 10 (1976).)

Failure to Act

Another major exception to the mistake-of-law rule is for crimes involving failure to act. For instance, with sex offender registration, generally, the person violates the law by willfully failing to register at his local police station. The law generally requires that the offender know, or reasonably should know, of his duty to register before he can be guilty of failing to register. That means that ignorance of the law—not knowing of the duty to register—may be a defense to the crime under certain circumstances. (See Lambert v. California, 355 U.S. 225 (1957).)


Some courts have allowed the mistake-of-law defense for the charge of criminal conspiracy. Conspiracy is an association of people with the shared intent to do something illegal. Some courts have said that if the person didn’t know the object of the conspiracy was illegal, he can’t be guilty.

Government Information

There are circumstances in which someone reasonably relies on information or representations that come from the government. The information the person relies on usually comes from a court decision or a statute, or directly from a government representative.

What if, reasonably relying on that information, the person takes an action that turns out to be illegal? Suppose the misinformation came from a court decision: Some courts have allowed the mistake-of-law defense when the defendant relied upon a court decision that had been reversed before he acted.

Bad Legal Advice

Typically, courts have rejected the mistake-of-law defense where the defendant’s misconception of the law was based on incorrect information provided by her attorney. In other words, bad advice from a lawyer generally isn’t an excuse for breaking the law. (But bad advice from a lawyer can sometimes be a defense where a crime requires specific intent and the defendant wants to prove that he didn’t have the requisite intent.)

Talk to an Attorney in Your Area

The difference between mistake of fact and mistake of law is often subtle, and courts vary in how they handle such mistakes. If you have been arrested or charged, you should talk to a qualified attorney in your area to find out how the law applies to the facts of your case.