We have considered the intent or mens rea requirement for criminal liability. Criminal statues generally impose an intent requirement. This raises the question, what if someone makes a mistake of a fact and did not intend to commit an act that gave rise to criminal liability? One can view mistakes of fact in terms of moral versus legal wrongs.

A moral wrong presumes a person can make a reasonable mistake and still be worthy of criminal punishment. The notion is that a person can manifest a bad character even when a mistake is involved. The question is whether the actors conduct was morally wrong assuming the facts the actor believed to be true were true.

A legal presumes a person is guilty of a criminal offense even if they make a reasonable mistake of fact. This is usually limited to situations where the actor believed he was committing a lesser crime than the one he actually committed. Thus, an actor’s conduct may not give rise to criminal liability if the defendant committed a crime, even though he believed he was not committing a crime.

State laws vary as to whether the courts are to look to moral or legal wrongs. The Model Penal Code or MPC, which provides a model for state laws, provides an example of what these laws say. The MPC provides that a mistake is a defense to a crime if it negates the mental state required to establish any element of the offense. It is irrelevant whether the offense would be identified as general intent or specific intent at common law.

The MPC provides one exception: the defense of mistake-of-fact is not available if the actor would be guilty of another offense, had the circumstances been as he supposed. Unlike the common law doctrine of legal-wrong, which maintains that the defendant is guilty of the higher offense, MPC only permits punishment at the level of the lesser offense.

Having considered the defense of mistake of fact, we can now consider crimes where the defense does not apply. Specifically, we can now consider strict liability crimes.