In the next few sections, we will explore situations in which the commission of what might otherwise be a crime does not result in punishment. Broadly speaking, the doctrines in this area of criminal law are grouped into “justification” and “excuse.” In this section, we will discuss the first kind of justification: self-defense.

Self-defense justifies a crime—more than excusing it, it affirms that what would otherwise be a criminal act is in fact desirable in a given situation. In cases of legal self-defense, our system treats a person who kills or injures as morally right, even when they kill intentionally.

Legalizing assault, killing, or other forceful actions inevitably devolves the state’s usual monopoly on the legitimate use of force, to individual persons capable of abusing it. Thus, legal self-defense raises several concerns. Should self-defense be a last resort? Must the defender respond with minimal force, or is any amount of force legitimate? Must the threat be actual, subjective, or objectively reasonable?

Different jurisdictions have created different systems. Compare the questions raised by situations such as ongoing abusive domestic relationships or an encounter with a stranger on the subway. As you read the following cases, consider the criminal system’s difficulty in managing individuals’ legal use of force, and notice how the law attempts to channel and contain that Pandora’s box.

Necessity may also justify action that would otherwise be criminal. The category is significantly narrower than self-defense, and claims of necessity are rarely successful. Necessity requires imminent and grave harm that results through no fault of the defendant. The defendant must take forceful action only when the benefits clearly outweigh the harms.

As you will see, the cases in this section often deal with significantly more extreme fact patterns than the self-defense cases. Why is the necessity justification narrowly construed?

Excuses, unlike justifications, do not assert that an action was morally right: instead, they deem an action to have been wrong, but less blameworthy under the circumstances. Every category of excuse, however, raises problems. In the case of duress, the question becomes what level of duress is necessary to excuse a crime, and what crimes can it excuse? As you will see, there is both a traditional duress doctrine and a reformed doctrine promoted by the Model Penal Code. Consider the differences between duress (an excuse) and necessity (a justification). What is the distinction between them, and why does blameworthiness attach to one but not the other?

The insanity excuse has been around for a long time, even as society’s social and scientific understandings of insanity have evolved. As an excuse, rather than a justification, insanity doctrine does not hold that the criminal act was morally correct, but rather that the insane person is not responsible for a morally wrong action.

The cases and readings in this section introduce some of the formulations of the insanity defense that are currently in use. Consider how the various formulations balance the moral and the medical. According to one insanity rule, the ability to tell right from wrong is central to the insanity inquiry. According to another, self-control is key, as an irresistible impulse may excuse culpability. The Model Penal Code applies a sort of hybrid. Each major test is followed in a variety of jurisdictions, and some jurisdictions follow yet another test or provide for no insanity defense at all. What does the sheer diversity of approaches and standards tell us about the insanity excuse? Should the very diversity of approaches implicate fairness concerns?

Consider why our criminal justice system may not seek to punish the insane. How does insanity implicate the traditional justifications of punishment (retribution, deterrence, incapacitation, and rehabilitation)? Since criminal punishment undoubtedly has a moral component, what should be the role of science in defining who is insane and who is excused due to insanity? Are those the same questions, or are they different?

Lastly, insanity may implicate more than the question of excuse. Even if someone is guilty, they may be “guilty but mentally ill.” Consider what role insanity or mental illness may play in establishing the other elements of a crime, such as mens rea.

If insanity and duress can excuse criminal behavior, why can’t social and economic distress affect culpability? The theory that environmental deprivation or a “rotten social background” should excuse criminal liability has been widely discussed. Some research indicates that growing up in impoverished, unstable, and violent environments can affect moral judgment—implicating the M’Naghten test—or other attributes such as self-control—perhaps implicating the irresistible impulse test. Nevertheless, the idea of an environmental deprivation excuse remains highly controversial, and there are many distinctions between insanity and environmental deprivation. As you read the following passages, consider both the similarities and the differences between environmental deprivation and the excuses we have studied. Remember, too, that criminal law is partly moral, and partly instrumental. What would be the practical effects of recognizing an environmental deprivation defense?