§ 12.02 Why Does a Factual Mistake Sometimes Exculpate?

§ 12.02 Why Does a Factual Mistake Sometimes Exculpate?

Aristotle believed that a person is not morally responsible for his actions unless he acts voluntarily, and that "[b]y the voluntary I mean . . . any of the things in a man's own power which he does with knowledge, i.e. not in ignorance."⁴

Use of the word "voluntary" in this context is potentially misleading because the term has multiple meanings in the criminal law.⁵ Nonetheless, it generally points us in the proper direction. An actor who is mistaken about some fact "does not have the same kind of opportunity to avoid doing evil that he would have if he knew what he was doing."⁶ Consequently, the mistaken actor's freedom of choice—and ultimately the moral basis for punishing him—is undermined.

A better way to understand why a mistake of fact may exculpate an actor is to observe that what makes a person's mistaken action "involuntary" has to do with his cognition (i.e., what he is aware of) rather than his volition (i.e., his capacity to control his conduct). From this realization, "the trail leads plainly to mens rea."⁷

Unfortunately, if the trail leads to "mens rea," then the common law leads us down two paths. This is because courts use the term "mens rea" in two ways: in a general sense to describe the actor's "vicious will," that is, his moral culpability for causing the social harm; and, in the narrower sense, to describe the particular mental state that is an express element of the offense.⁸ A mistake of fact may negate the actor's "mens rea" in one or both senses of the term.

In some cases, proof that a person was factually mistaken demonstrates that, despite appearances, he acted in a morally blameless manner and that, therefore, he is not deserving of punishment for causing the social harm. In this sense a mistake of fact negates "mens rea" in the "culpability" meaning of the term.

A mistake of fact may also negate "mens rea" in the "elemental" sense. That is, because of a mistake, a defendant may not possess the specific state of mind required in the definition of the crime. In such circumstances, the defendant must be acquitted because the prosecutor has failed to prove an express element of the offense.

Once one sees this relationship between mistake and mens rea it is easy to see that the rule that a mistake of fact is exculpatory is not a special rule—either the actor had the mens rea required to be guilty of the crime or he did not.

Courts frequently characterize mistake-of-fact as a...