My discussion of this important subject will elaborate answers to the following questions:
- Does imprisonment reduce crime? Yes.
- Do many crimes cause considerable harm and hardships to victims? Yes.
- Does America imprison too many people? In light of my answers to 1) and 2) you might expect my answer to this question to be “no”, but it is a strong “yes”.
Imprisonment reduces crimes against the general public if only because of the incapacitation effect; that is, person in prison cannot commit crimes against the public-they can and do commit many crimes against other prisoners. For certain crimes, imprisonment also has a deterrent effect, so that potential offenders are deterred from committing crimes by the prospects of prison terms, especially when the probability of apprehension is not negligible.
This conclusion does not deny that imprisonment raises the likelihood that some prisoners will commit crimes when they are released because their skills at legal employment eroded while in prisons, or they learned in prison how to be better criminals, or they become blacklisted for certain jobs, or for other reasons. Nevertheless, Levitt’s study cited by Posner and other studies find that on balance imprisonment reduces crime. The main disagreement is over whether the whole effect of imprisonment on crimes comes from the incapacitation effect, or whether some is also due to deterrence. I believe deterrence is also at work.