The approach based on general deterrence aims to dissuade others from following the offender’s example. Less concerned with the future behaviour of the offender himself, general deterrence theories assume that, because most individuals are rational, potential offenders will calculate the risk of being similarly caught, prosecuted, and sentenced for the commission of a crime. Deterrence theory has proven difficult to validate, however, largely because the presence of many intervening factors makes it difficult to prove unequivocally that a certain penalty has prevented someone from committing a given crime. Nevertheless, there have been occasional examples showing that some sentences can have a strong deterrent effect. Laws designed to prevent driving under the influence of alcohol (e.g., by setting a maximum legal level of blood alcohol content) can have a temporary deterrent effect on a wide population, especially when coupled with mandatory penalties and a high probability of conviction.

Proponents of capital punishment have claimed that it serves as an effective deterrent against murder (see homicide). Research in the United States, however, has shown that some jurisdictions that use the death penalty have higher murder rates than those that do not. There are several interpretations of this pattern. Some argue that use of the death penalty is a response to, but not a cause of, high murder rates, while some maintain that it has a brutalizing effect on society that increases the incidence of murder by instilling a lower regard for human life. (See below Effectiveness of punishment.)

Another form of deterrence, known by the term denunciation, utilizes public condemnation as a form of community moral education. In this approach, a person found guilty of a crime is denounced—that is, subjected to shame and public criticism. Although denunciation is closely associated with general deterrence through fear—and many courts have imposed sentences designed to achieve both objectives simultaneously—there is an important distinction between them. Education through denunciation is generally aimed at discouraging law-abiding citizens from committing criminal acts. Its object is to reinforce their rejection of law-breaking behaviour. Most people do not steal because they believe that stealing is dishonest; a sentence imposed on a thief reinforces that view. General deterrence through fear is aimed at those who avoid law-breaking behaviour not on moral grounds but on the basis of a calculation of the potential rewards and penalties involved.

Individual deterrence

Individual deterrence is directed at the person being punished: it aims to teach him not to repeat the behaviour. It is also the rationale of much informal punishment, such as parental punishment of children. Theoretically, the effectiveness of individual deterrence can be measured by examining the subsequent conduct of the offender. Such studies often have been misleading, however, because in most cases the only basis for proving that the offender repeated his crime is a further conviction. Because a high proportion of crimes do not result in convictions, many offenders who are not reconvicted after being punished may have committed additional crimes. Furthermore, the general pattern of “aging out” of crime (i.e., the fact that criminal behaviour peaks in the late teens and early 20s and declines rapidly thereafter) contributes to the difficulty of measuring the effectiveness of particular deterrence strategies.

Theories of deterrence and retribution share the idea that punishments should be proportionate to the gravity of the crime, a principle of practical importance. If all punishments were the same, there would be no incentive to commit the lesser rather than the greater offense. The offender might as well use violence against the victim of a theft if the penalty for armed robbery were no more severe than that for larceny.