Can fear discourage crime? There has been much debate over whether deterrence works. Proponents assert that punishment deters if it is administered with celerity (swiftness), certainty, and severity. A distinction needs to be drawn between general versus specific deterrence. General deterrence uses the person sentenced for a crime as an example to induce the public to refrain from criminal conduct, while specific deterrence punishes an offender to dissuade that offender from committing crimes in the future. Critics point to the high recidivism(relapse into crime) rates of persons sentenced to prison as evidence of the lack of effectiveness of specific deterrence. Critics also note that there are limits to the impact of general deterrence. Some crimes, such as crimes of passion and crimes committed while under the influence of drugs, can't be deterred because their perpetrators don't rationally weigh the benefits versus the costs (which include punishment) before breaking the law. Finally, research evidence suggests that the deterrent effect of punishment is weak.

A popular reason for punishment is that it gets criminals off the streets and protects the public. The idea is to remove an offender from society, making it physically impossible (or at least very difficult) for him or her to commit further crimes against the public while serving a sentence. Incapacitation works as long as the offenders remain locked up. There is no question that incapacitation reduces crime rates by some unknown degree. The problem is that it is very expensive. Incapacitation carries high costs not only in terms of building and operating prisons, but also in terms of disrupting families when family members are locked up.