“How are prisons supposed to produce stability through controlling what counts as crime? Four theories condense two and a quarter centuries of experience into conflicting and generally overlapping explanations for why societies decide they should lock people out by locking them in. Each theory, which has its intellectuals, practitioners, and critics, turns on one of four key concepts: retribution, deterrence, rehabilitation, or incapacitation. Let’s take them in turn. The shock of retribution—loss of liberty—supposedly keeps convicted persons from doing again, upon release, what sent them to prison. Retribution’s specter, deterrence, allegedly dissuades people who can project themselves into a convicted person’s jumpsuit from doing what might result in lost liberty. Rehabilitation proposes that the unfreedom of”