There are two types of mistakes you can make: mistakes of fact and mistakes of law. In most cases, only mistakes of fact can serve as defenses to criminal charges. But, there are a few select situations in which a mistake of law can be a defense.

What Is a Mistake of Fact?

A mistake of fact is just that: a mistake pertaining to some fact. For example, if you are 35 years old but I think you are 34, I have made a mistake of fact. A mistake of fact can serve as a defense.

When Is a Mistake of Fact a Defense?

A mistake of fact is only a defense if it negates a material element of the crime. Every crime has elements that the government must prove in order to convict you. For example, one element of theft is that you must intend to deprive the owner of his/her property permanently. If your mistake of fact makes it such that this or some other element is not present, you have a defense and cannot be convicted.

Not only must you mistake of fact negate an element of the crime, it must also be an honest mistake. In many states, your mistake must also be a reasonable one.

What Is an Example of a Mistake of Fact Defense?

The concept of mistake of fact can be very complicated. Here’s an example that may help. Suppose you are working in a library and you brought a laptop with you. When you leave, you take someone else’s laptop, honestly believing it is yours. You have made a mistake of fact: you thought the laptop was yours, but it isn’t. This mistake negates the intent to the "deprive permanently" element of theft. This mistake also is an honest, reasonable mistake. So, you have a defense to theft charges in this example.

What Is a Mistake of Law?

A mistake of law is where you are mistaken or ignorant about the law. For example, if you believe that you don’t have to come to a complete stop at a "Stop" sign when there are no other cars at the intersection, you have made a mistake of law. Whether there are cars or not, you must come to a complete stop. In almost every case, you will not be allowed to argue that you didn’t know or misunderstood the law. That is, it won’t be a defense.

When Can a Mistake of Law Be a Defense?

There are a few very limited circumstances in which a mistake of law can serve as a defense to criminal charges. The circumstances in which a mistake of law can serve as a defense include:

  • When the law is not published
  • When you relied upon a statute that was later overturned or held to be unconstitutional
  • When you relied upon a judicial decision
  • When you relied upon an interpretation by an appropriate official

In most states, your reliance on any of the above listed sources must be reasonable. So, if your case is pending appeal, it is not reasonable to rely upon the decision reached so far. Also, it is not a defense to claim that you relied upon an interpretation of the law from your lawyer.

Do I Need a Lawyer?

If you are arrested or facing criminal charges, you should consult a lawyer as soon as possible. An experienced criminal defense lawyer can advise you of your rights and defenses. The distinction between mistake of law and mistakes of fact is very fuzzy and it can be easy to confuse the two. A lawyer with experience in criminal law can help clarify the issue and help determine if you have a defense available.