Retribution- This is about justice - criminals suffer in exchange for the suffering they caused
Rehabilitation - Helping offenders so that they are less likely to commit crimes in the future
Deterrence - Prison is a negative consequence of criminal behaviour and so this makes the offender less likely to commit crimes
Protection - Imprisoning an offender also protects the public from them committing further crimes e.g. a serial killer will be unable to kill any more people while locked up in prison
Institutionalisation - If someone spends too long in prison, they may come to see prison life as normal and find life outside of prison difficult
Mental health problems - The mental breakdowns of 'prisoners' in the Stanford Prison Study demonstrates potential mental issues resulting from imprisonment. Further, Fazel et al (2011) found rates of suicide in prison were roughly 3 times higher than in the general population.
Recidivism - i.e. reoffending - rates after being released from prison are high
According to the UK Ministry of Justice proven reoffending statistics, around 25% of adult offenders reoffend within 1 year of being convicted of a crime
However, recidivism is negatively correlated with length of sentence e.g. offenders given custodial sentences longer than 10 years are significantly less likely to reoffend than offenders given custodial sentences of 6 months or less
Rehabilitation schemes in prison may result in the offender changing their life for the better . e.g. an offender who used to crime to support themselves financially may learn skills that enable them to make an honest living upon release. This results in a positive contribution to society and gives the offender a second chance
e.g., institutionalised prisoners may be more likely to commit crimes when released, which is the opposite of deterrence. Similarly, prison may reinforce criminal behaviour, which is the opposite of rehabilitation. These criticisms are supported by the high rates of recidivism described above