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a. Criticism of rule: Requiring the defendant not to make an unreasonable mistake has often been criticized, on the grounds that it may allow the defendant to be convicted of a crime requiring intent (e.g., first-degree murder) when his only relevant mental state was negligence. For instance, suppose the defendant is somewhat stupid and somewhat paranoid, and he reasonably believes that X, his acknowledged enemy, who has reached into his pocket, is about to shoot him. If in reality, X is merely reaching for a handkerchief, and D fatally shoots him in “self defense,” under the common-law rule his negligent mistake is wiped out—the case is treated as if D behaved maliciously. This result has seemed to many to be unjust.

i. Model Penal Code view: Accordingly, the Model Penal Code requires, as to all the defenses discussed here, merely that the defendant really believe (whether reasonably or not) that the facts are such that the defense is merited. The only exception to this rule is that, if the defendant is prosecuted for an act that may be committed “recklessly” or “negligently,” he will lose the defense if his mistake was “reckless” or “negligent,” as the case may be. M.P.C. § 3.09(2).

Example: Consider the hypothetical given above, in which D fatally shoots X, in the unreasonable and mistaken belief that X was about to kill him. Under the Model Penal Code approach, D will be able to assert the defense of self-defense to a charge of first-degree murder, since the definition of that crime provides that the killing must be committed “purposely or knowingly,” or with “extreme indifference to the value of human life.” (See M.P.C. § 210.2(1)). But if the charge against D is manslaughter, he will not be able to assert self-defense if it is shown that his mistake was “reckless,” since manslaughter, under the Code, may be committed recklessly. (See M.P.C. § 210.3(1)(a)). Similarly, self-defense would be no defense against a charge of negligent homicide (M.P.C. § 210.4) if the mistake were shown to have been a negligent one.

C. Overlapping of defenses: In some situations, more than one of the defenses in this chapter might be applicable. For instance, a homeowner who shoots a burglar might assert self-defense, defense of others (his family), prevention of crime (larceny), and arrest. Since, particularly under the common-law approach, there may be significant disparities in the requirements for these defenses (e.g., the consequences of a reasonable mistake), it can be important to pick the correct defense to assert.

1. Model Penal Code attempts unified rules: For this reason, the Model Penal Code draftsmen have attempted to reduce the disparities in the rules governing the various defenses. For instance, as noted, an unreasonable but genuine belief in the need to assert any of these defenses will not negate the defense under the Code, unless the offense charged is one which may be committed recklessly or negligently.


A. Nature of duress: A defendant can be said to have committed a crime under duress if he performed it because of a threat of, or use of, force by a third person sufficiently strong that the defendant’s will was overborne. The term applies to force placed upon the defendant’s mind, not his body.

Example: Suppose X forces D to rob Y, by threatening D with immediate death if he does not. This is duress, since the force from X operates on D’s mind. But if X had given D an epilepsy-producing drug, so that D went into convulsions and attacked someone, D would not raise the defense of duress; instead, he would assert that he had not committed any voluntary act, and therefore had no liability (see supra, p. 16).

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