Our assessments of the severity of prison sentences rest on a fundamental mistake. We deem inmates as receiving equal punishments when they are incarcerated for the same period of time under the same conditions. While doing so puts the inmates into identical situations, it does not change their situations equally unless they started out in identical circumstances. It is the amount by which we change offenders’ circumstances that determines the severity of their sentences.
In tort and contract law, we understand what a defendant has done to a plaintiff by examining the change in the plaintiff’s condition caused by the defendant. To assess the amount of an injury, we compare an injured party’s condition relative to the condition the party would have been in under other circumstances. For some reason, however, when we consider the treatment of prisoners, we ignore their baseline conditions.
To accurately assess punishment severity, I argue, we must compare an offender’s condition in prison relative to his baseline condition. This is the approach we use to measure the severity of certain kinds of punishment, like monetary fines. Fines specify an amount by which to change an offenders’ wealth. We never use fines to set equally culpable offenders’ net worth to the same level. But we do use prison to set equally blameworthy offenders’ liberties to the same level, even though offenders are deprived of liberty to different degrees depending on their baseline levels of liberty.
When we recognize the comparative nature of punishment, we see that, by putting two offenders in prison for equal durations, the offender with the better baseline condition may be punished more severely than the offender with the worse baseline condition. This means punishing one offender more severely than the other, even when they are equally culpable. I suspect that most people care little about correcting such inequalities. The bottom line, I suspect, is that people care less about true punishment equality and proportionality than they realize.