Like many of you, I have a neighbor with an excitable car alarm. It goes off if someone drives by at just the right speed, if the humidity is right, or if a large insect lands on the hood. Worse, it seems most sensitive at night. (Perhaps that’s just when he parks in front of my house.) I’d like to do something about it, to preempt it before it preempts another night of sleep. One possibility, which is beyond my competence, is repairing it myself. Another, which I have so far resisted, is to get out my tool box and remove the offending device. Private law has a kinder and gentler solution: I can get an injunction. Rather than trying to sue my neighbor for minuscule damages each time he wakes me, and waste a huge amount of both of our time in the process, I can enlist the state’s support, and have it act preemptively to prevent him from waking me.

Why do we fear preventive detention and believe that it requires special justification? Citizens in free, democratic societies are accustomed to substantial limitations on liberty that are justified morally and politically by the “common good.” Avoiding serious danger is a greater good than most, but the power of the state to confine dangerous people or to reduce danger by equally oppressive intrusions is considered especially fearsome. The usual, and generally uncontroversial, justifications given for such deprivations of liberty are that the person has culpably committed a criminal offense or that the agent is not responsible for the danger he or she presents. Criminal imprisonment and various forms of civil commitment, for example, which preempt potentially dangerous conduct by incapacitation, are considered reasonable deprivations of liberty in such cases. But in neither case is the state confining on purely preventive grounds a responsible agent who has done no wrong. In contrast, pure preventive detention is an anathema, we believe, because polities devoted to liberty and autonomy have no moral or political warrant to confine or similarly oppress innocent, responsible agents. What could justify such a vast intrusion on the liberty of such agents to pursue their projects?I recognize that the state has an uncontroversial right to quarantine innocent, responsible agents if such agents have communicable diseases and no less intrusive intervention will prevent infection of others. Although many forms of communicable disease can be spread by conduct, the justification of pure quarantine requires no action or potential action. It is a purely public health measure directed toward microorganisms that has the undesirable effect of limiting freedom of action. This article addresses only the preemption of dangerous conduct, which might in some cases include the transmission of disease. See generally Michael Corrado, Punishment, Quarantine, and Preventive Detention, 15 Crim. Just. Ethics 3 (Summer/Fall 1996).

Sometimes it is morally permissible to prevent someone from performing a wrongful act by harming him before he has a chance to act. It is permissible, for example, to kill someone you reasonably fear is about to kill you. Under other circumstances, however, it may only be permissible to threaten to harm someone to discourage him from performing a wrongful act. It is not always permissible straightaway to harm him. A military commander, for example, may threaten an enemy with disproportionate retaliation, even though it would not ordinarily be permissible to carry it out.

The best test of whether an intellectual problem is genuinely worthwhile is whether there exists a Jewish joke on point. By that quite exacting standard, the problem of preemptive action is certainly an important one. To be sure, the joke that comes to mind is not especially funny, but that is not what counts. It is the existence of the joke, not its funniness, that matters.