It is puzzling that American criminal law recognizes self-defense while rejecting the conceptually similar defense of necessity. Necessity applies where pressing circumstances provoke the defendant to commit an otherwise unlawful act, while self-defense applies where an assailing person does so. Different treatment would make sense if the two defenses were morally distinguishable. But they are morally equivalent, whether considered from the perspective of natural law, social contract theory, or utilitarianism. Rather, the motivation appears to be that the necessity defense, unlike self-defense, implies biological determinism, calling into question the criminal law’s traditional assumption that human beings exercise free will in choosing their actions. And, as its treatment of the necessity defense indicates, American criminal law does not simply proceed from an assumption of free will but silences any contradiction. Such a stance means not only that the necessity defense cannot be accommodated, but also that the legal system cannot make use of the insights of the sciences and social sciences to the extent that they describe human behavior deterministically. However, it may be better for the law to embrace a more salutary kind of inconsistency, one that entertains the possibility that the law is capable of moral improvement and self-correction.
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