The most recently formulated theory of punishment is that of rehabilitation—the idea that the purpose of punishment is to apply treatment and training to the offender so that he is made capable of returning to society and functioning as a law-abiding member of the community. Established in legal practice in the 19th century, rehabilitation was viewed as a humane alternative to retribution and deterrence, though it did not necessarily result in an offender receiving a more lenient penalty than he would have received under a retributive or deterrent philosophy. In many cases rehabilitation meant that an offender would be released on probation under some condition; in other cases it meant that he would serve a relatively longer period in custody to undergo treatment or training. One widely used instrument of rehabilitation in the United States was the indeterminate sentence, under which the length of detention was governed by the degree of reform the offender exhibited while incarcerated.
Theories in conflict
In the practical operation of a sentencing or penal system, theories of punishment often come into conflict. A lenient sentence (such as probation) designed to rehabilitate an offender may fail to express society’s rejection of the behaviour or to provide an effective deterrent to others; a sentence that requires the offender to submit to a compulsory program of treatment or training for a long period may conflict with the idea of retribution as a limiting principle (a constraint on excessive or unfair punishment); a sentence of unusual severity, designed to make an example of the offender as a warning to others, conflicts with the principles of rehabilitation and proportionality; and a sentence whose object is incapacitation may fail to satisfy those who favour rehabilitation and proportionality. The operation of any sentencing system requires officials to choose between different theories in different cases; no single theory provides a system suitable for all cases.