In the course of your legal studies, I'm sure you've come across the concepts "mistake of fact" and "mistake of law." But just what do these concepts entail? According to the Cornell Legal Information Institute, a mistake of fact is "[a]ny mistaken belief other than a mistake of law. Examples include erroneous beliefs about the meaning of some term or about the identity of some person. In criminal law, a mistake of fact can usually operate as a defense so long as it is reasonable. With crimes that require specific intent, even an unreasonable mistake of fact might work as a defense." Conversely, a mistake of law is a "[m]istake about the legal effect of a factual situation." But what does that mean exactly? Where do these concepts arise? They are criminal defenses of mistake, i.e. a criminal defendant may raise them as a defense of his or her conduct.
"In many situations, a criminal defendant may wish to argue that he or she never intended to commit a crime and that the criminal act that occurred was a result of a mistake of facts regarding the circumstances of the crime or a misunderstanding concerning the law at the time. Such mistakes of fact can be applied to a variety of criminal activities, but mistakes of law are only rarely allowed as full defenses to criminal conduct." Criminal Defenses of Mistakes of Fact and Mistakes of Law.
Essentially, a "mistake of fact" arises as a defense when the defendant argues they "misunderstood some fact that negates an element of the crime" whereas a "mistake of law" arises when the criminal defendant argues that they "misunderstood or [were] ignorant of the law as it existed at the time."
According to U.S. v. Dean, "[I]gnorance of the law or a mistake of law is no defense to criminal prosecution in the United States." Therefore, according to Moncrief v. State, Com'r of Ins., "[T]he courts universally recognize that ignorance or mistake of law will not excuse an act in violation of the laws so long as the laws clearly and unambiguously proscribe the conduct alleged." It is, therefore, extremely difficult to successfully argue the defense of mistake of law in a criminal trial. A "mistake of fact" defense may more easily succeed in a criminal trial. According to U.S. v. Bowling, "Where the intent of the accused is an ingredient of the crime, its existence is a question of fact, which must be submitted to a jury. Morissette v. United States, 342 U.S. 246, 274, (1952). A mistake-of-fact defense relieves a person of criminal liability where a reasonable mistake of certain facts means that the person did not have the culpable mental state required for the commission of the offense." While individual court systems may define and interpret what qualifies as a "mistake of fact" or a "mistake of law" and what does not, the essential concepts remain the same. Hopefully you now have a better understanding of these defenses and can utilize this knowledge to your advantage in the future.