The excusing conditions of the criminal law are variations of the theme "I couldn't help myself' or "I didn't mean to do it." In this respect the defenses known as necessity, duress, insanity and mistake of law are but extensions of homely, routine apologies for causing harm and violating the rules of social and family life. While we use the plea "I couldn't help myself" to cover the full range of excusing circumstances, each of the formal excuses of the criminal law has a limited sphere. As a general matter, these spheres are dictated by the type of circumstances rendering the conduct excusable. If the excusing circumstances are natural phenomena, the appropriate excuse is necessity. Standard cases are those of the starving man who steals a loaf of bread or the shipwrecked sailor who dislodges another man from the only life-sustaining plank at sea. If the excuse derives from intimidation exerted by another human being, the appropriate excuse is coercion or duress. Thus, if the actor steals or rapes only because a gunman threatens to kill him if he does not, the defense of duress would come to play. In a third type of case, the distortion in the actor's conduct is attributable neither to natural circumstances nor to another human being, but to his own psychological make-up. It is here that we speak of legal insanity as a defense. Whether the formula of insanity is the restrictive M'Naghten rule or the more liberal Durham test, the inquiry is the same: Is there something about the defendant's psychological condition that makes it credible for him to say, "I couldn't help myself."
The excuse of mistake of law warrants special notice. An individual might engage in seemingly innocuous conduct, such as carrying a pocket knife, and find himself in violation of the criminal law. Nothing compels him to carry the knife. If he has an excuse, it would be that he "didn't mean" to violate the law. In this type of case, the distortion of the actor's conduct derives not from internal or external pressures, but from ignorance – ignorance that might be beyond his control.
These four excusing conditions bear several common traits. They all speak in the idiom of involuntariness. The claim is not that there was no act at all (as if the actor suffered an epileptic seizure), but that the actor, in Aristotle's words, "would [not] choose any such act in itself." Were it not for the conditions of necessity, duress, insanity or ignorance of the law, the actor would not have violated the law. Therefore, his act seems to be attributable to circumstances rather than to his character. The act does not tell us what kind of person the actor is. The premise seems to be that if a violation of the law does not accurately reveal the actor's character, it is unjust to punish him for what he has done."
Criminal Law | Law | Law and Philosophy
Center on Global Governance
George P. Fletcher,
The Individualization of Excusing Conditions,
S. Cal. L. Rev.
Available at: https://scholarship.law.columbia.edu/faculty_scholarship/1023