There are actually three different justifications for prison: * Retribution ("a punishment") * General prevention ("a jailed person cannot keep hurting others

There are actually three different justifications for prison: * Retribution ("a punishment") * General prevention ("a jailed person cannot keep hurting others and prison threat is a deterrent") * Special prevention (rehabilitation) Last time I looked, most countries are mostly for general prevention with a pinch of special prevention. Retribution is not currently defensible philosofically or technically, though some people errounesly think it's the basis of the system.