Mistake

Due to the influence of the Model Penal Code (MPC), the traditional approach to exculpatory mistakes has been largely replaced by the "elements approach": a mistake exculpates if and only if it negates the mens rea (criminal mental state) that the legislature has required for the particular element of the crime. For example, if the legislature requires knowledge of X in its definition of the crime, any belief that X does not exist—any mistake, legal or factual, reasonable or not—will negate the crime, since belief in ~ X is legally inconsistent with "knowledge of" X. Similarly, if recklessness with respect to the existence of X is what the legislature has required, then the defendant's belief in ~ X will exculpate her unless she was reckless in believing ~ X (she was aware of a substantial and unjustifiable risk of X). (See MPC § 2.02(2)(c), definition of recklessness). If the legislature requires only negligence with respect to X, the defendant's belief in ~ X will exculpate only if the belief is not negligent. Finally, if the legislature makes the existence of X a matter of strict liability—no mens rea is required with respect to X—then the defendant's mistake regarding the existence of X is immaterial to her guilt under the statute. (The application of this approach to mistakes when the crime requires acting with the "purpose" of producing X or engaging in X is not as straightforward. Although some commentators have suggested that the defendant's belief in ~ X negates any purpose to produce or engage in X, the better analysis is that one can have a purpose to X in the criminal law sense even if one does not believe X will result. For example, if the Jackal takes what he knows is a one in one thousand shot at DeGaulle, hoping he will succeed in hitting him but believing he will not, he acts with criminal purpose. For if he hits DeGaulle and kills him, the homicide is surely purposeful. The Jackal will hardly be heard to claim that he lacked the required purpose merely because he believed his chances of success were poor.)

The reform here is really nothing more than the recognition that mens rea requirements logically entail certain treatment of mistakes, and that therefore there is no sense in treating exculpatory mistakes under a rubric separate from mens rea. The old approach is confusing and results in punishment for negligent, i.e., unreasonable, mistakes even though arguably a mens rea more culpable than negligence is statutorily required.

The new approach to exculpatory mistakes has also been extended beyond mistakes regarding elements of crimes to mistakes that bear on defense. Under the traditional approach, for example, a defendant who makes an unreasonable mistake regarding whether he is being attacked and thus may employ force in self-defense is deprived of the privilege of employing such defensive force. Under the new approach, exemplified by the Model Penal Code, the defendant retains the privilege except against a charge that reflects his actual culpability. Thus, if his mistake is only negligent, he may be convicted only of the negligent use of force. If it is a reckless mistake, he may be charged with reckless use of force. But if he has been genuinely mistaken, and he would have been entitled to use force had things been as he believed, he may not be charged with any degree of use of force higher than recklessness.

The Model Penal Code has also extended its elements approach to cover cases where the defendant's mistake exculpates him of the offense he otherwise committed but inculpates him in a different crime, one he mistakenly believed he was committing. Thus, if the defendant kills Polly, honestly mistaking her for a swan, and killing swans is itself prohibited, then the defendant may be held liable under the Model Penal Code § 2.04(2) for that degree of homicide that carries the same penalty as the crime (swanicide) he believed he was committing. In essence, the Model Penal Code constructs an artificial crime out of an attempt to commit one crime and commission of the actus reus (prohibited conduct) of another.

If the reforms above are basically analytic, the reformers were also prescriptive when it came to exculpatory mistakes about the existence or meaning of the criminal statutes themselves as opposed to mistakes about matters of fact or law that are elements of particular criminal statutes. They urged retention of the traditional position that ignorance of the criminal law did not in most cases excuse one from criminal liability. The Model Penal Code is illustrative. Section 2.02(9) prescribes that in interpreting a criminal statute, knowledge or belief regarding the existence or meaning of the criminal statute is not to be read into the statute as a required mental state. And section 2.04(3) lays down conditions for a quite narrow excuse of mistake of criminal law. (Basically, under MPC § 2.04(3), mistakes regarding the existence or meaning of a criminal statute excuse only when the statute has not been published or when the defendant has relied on an official but erroneous interpretation of the statute.)