Justification: Self-Defense

Various theories have been advanced, none of which are entirely satisfactory, to account for the law's recognition of the right to use defensive force.

Excuse. Under Blackstone's view, or the social theory of self-defense, the rights of the defender are constrained by acknowledging the interests of society; self-defense is only legitimate when it promotes social welfare. For Blackstone, the use of force in the defense of others, apprehending felons, crime prevention, and punishing convicted criminals promoted interests beyond those of who was employing the force and was justifiable. In contrast, the use of force in self-defense only promoted the interests of the defender (not society's interests) and was only excused. The basis for the excuse was that self-preservation is instinctual. The weakness of Blackstone's theory is that it failed to see that a defender vindicating his interests against a wrongful aggressor might benefit society as well.

The causation theory suggests that but for the aggressor's attack the victim would not have employed force and thus it is not the defender, but the aggressor who is responsible for the harm to the aggressor. Not being responsible, the defender's force is excused. Under a character theory of excuse, it is the aggressor, and not the innocent defender, whose acts manifest a bad character. Thus only the aggressor should be held liable and the defender is excused. Explaining self-defense as merely an excuse is typically thought unsatisfactory because of the intuition that the nature of defensive force is not wrongful.

Justification. The private punishment theory justifies defensive force because it inflicts punishment on a deserving wrongdoer instead of, or in addition to, the state. The theory is reflected by the common sentiment heard on the street when a robber or rapist is killed by the victim in self-defense: "He got what he deserved." The philosopher Robert Nozick partially develops the analogy between self-defense and punishment by suggesting that an aggressor's punishment should be reduced by the amount of suffering inflicted upon the aggressor by the defender. Perhaps the original source of the theory may be Blackstone's observation that if a petty thief is not executed by the state for his crime then lethal force is impermissible to prevent the theft. Analogizing Blackstone's observation to self-defense, if a minor assault is not an offense serious enough to warrant the death penalty, then lethal force is impermissible in defense of the assault. Yet the analogy breaks down because permissible defensive force fails to correspond with an aggressor's punishment by the state. For example, though lethal self-defense is permissible against a violent rape, the death penalty is a constitutionally disproportionate punishment for rape (Coker v. Georgia, 433 U.S. 584 (1977)).

A number of utilitarian-based arguments might be made to justify defensive force. In a deadly conflict in which one person will inevitably die it is better that the innocent defender live and the wrongful aggressor die. This is so because, first, an innocent person's life is worth more than the aggressor's; the aggressor's death constitutes the lesser evil. But this argument violates the principle that everyone is of equal moral worth; no life is more valuable than another. Second, it is better that the aggressor be killed because of the general danger the aggressor poses to future victims. But in many cases of physical conflict it is difficult to ascertain which is the culpable party, or alternatively both parties may be partially at fault (Garrett Epps). Third, permitting the use of defensive force will serve to preserve life by deterring wrongful aggression (lawful resistance creating a disincentive for wrongful aggression) (Herbert Wechsler and Jerome Michael). But whether violence deters violence or only begets more violence is exceedingly controversial.

The moral forfeiture theory maintains that by threatening to violate another's right to life or sphere of autonomy, the aggressor forfeits or loses the right to life or autonomy. Defensive force against the aggressor is permissible because it does not violate any right of the aggressor to be free from force. This is so because by the aggressor's own attack, the aggressor has lost the right to life or autonomy. The theory has been extensively criticized because it would seem to justify disproportional, unnecessary, and retaliative force. That is, force would be justified against an aggressor who abandoned the attack, was retreating, or disabled, or who no longer posed a threat to the defender. The philosopher Judith Jarvis Thomson has, in part, rehabilitated the theory to avoid this criticism. The forfeiture of the right to life is made contingent on a present or imminent threat to violate another's right to life; once the aggressor has ceased to be violating another's right to life, the aggressor regains the right to life.

The theory of personal autonomy, championed by the philosophers Immanuel Kant, Georg Hegel, and the criminal theorist George Fletcher, emphasizes not the devaluation of the aggressor but the enhancement of the defender's rights. The theory holds that wrongful aggression breaches the sphere of autonomy enjoyed by everyone as well as affronting the abstract concept of Right itself. Since Right must never yield to Wrong, the victim of wrongful aggression not only has the right but the duty to exercise defensive force. Or putting it in Locke's terms, aggression breaches the social contract and returns both aggressor and defender to the state of nature establishing a state of war between the combatants. Since yielding to aggression enslaves the victim, the victim is entitled to use any and all necessary force. But in its absolutist conception of the defender's rights, lethal defensive force must be employed if it is necessary to prevent even a minor assault. Critics argue that the theory goes too far in authorizing disproportional force.

Sanford Kadish's right to resist aggression theory postulates that everyone has a right against the state for protection from wrongful aggression. The state licenses the right of self-defense to its citizens because of practical difficulties in providing round-the-clock protection. But because the use of defensive force is only licensed or derived from the state, the state can place reasonable limits on its use and impose, for example, necessity and proportionality requirements. Though avoiding the criticisms of the latter two theories, it succumbs to a different problem. Self-defense is generally regarded as an inalienable, moral right not merely a civic or political right.