Rehabilitation:[k] Theories of rehabilitation claim that the experience of being imprisoned will cause people to change their lives in a way that will make them productive and law-abiding members of society once they are released. However, this is not supported by empirical evidence, and in practice prisons tend to be ineffective at improving the lives of most prisoners.[98] As Morris and Rothman (1995) point out, "It's hard to train for freedom in a cage."[97] While the view of prisons as centers of rehabilitation was popular during the early development of the modern prison system, it is not widely held anymore, and has mostly been replaced by theories of deterrence, incapacitation, and retribution.[99]
Deterrence: Theories of deterrence claim that by sentencing criminals to extremely harsh penalties, other people who might be considering criminal activities will be so terrified of the consequences that they will choose not to commit crimes out of fear. In reality, most studies show that high incarceration rates either increase crime, have no noticeable effect, or only decrease it by a very small amount.[100] Prisons act as training grounds for criminal activity, form criminal social networks, expose prisoners to further abuse (both from staff and other prisoners), foster anti-social sentiments towards society (law enforcement and corrections personnel in particular), fragment communities, and leave prisoners with criminal records that make it difficult to find legal employment after release. All of these things can result in a higher likelihood of reoffending upon release.[101][102]
Incapacitation: Justifications based on incapacitation claim that while prisoners are incarcerated, they will be unable to commit crimes, thus keeping communities safer. Critics point out that this is based on a false distinction between "inside" and "outside", and that the prisoners will simply continue to victimize people inside of the prison (and in the community once they are released), and that the harm done by these actions has real impacts on the society outside of the prison walls.[103]
Retribution: Theories of retribution seek to exact revenge upon criminals by harming them in exchange for harms caused to their victims. These theories do not necessarily focus on whether or not a particular punishment benefits the community, but are more concerned with ensuring that the punishment causes a sufficient level of misery for the prisoner, in proportion to the perceived seriousness of their crime. These theories are based upon a belief that some kind of moral balance will be achieved by "paying back" the prisoner for the wrongs they have committed.[104]