Most penal laws across the world include sentences of incarceration time for crimes. For example, punishment for federal crimes in the U.S. focuses on a sentencing table determining months of imprisonment under the Federal Sentencing Guidelines. The Federal Sentencing Guidelines do not allow for parole, limit good-time credit to a maximum of 54 days per year of imprisonment, and link probation to the sentence of months of imprisonment.^

Even when imprisonment is the predominate punishment, months of imprisonment need not be the primary measure of punishment. In the latter part of the eighteenth century, a legal scholar declared:

I would measure the confinement, not by the duration of time, but by quantity of work {done by the prisoner while imprisoned}, in order both to excite industry, and to render it more voluntary.^

Prison labor is only one possible alternative measure of punishment in prison. Criminal laws could specify qualitatively graded retributive punishment such as light, medium, or severe punishment. Judges would then interpret the duration of imprisonment with respect to the prisoners’ individual circumstances. Alternatively, the criminal justice system could operate on a rehabilitative or public safety standard such as “imprisonment until no longer an unacceptable threat to public safety.” Prison administrators would evaluate prisoner characteristics and behavior and consider them relative to accumulating data on public-safety risks. They would estimate the public-safety threat from the individual prisoner relative to the standard level of unacceptable threat.

The legal academy has recently produced law review articles arguing about the relevance of the subjective experience of punishment. These articles are helpful for gaining understanding of the subjective experience of punishment.