I have written a number of posts on the 4 theories of punishment and compared and contrasted them. In the order of decreasing sophistication, the theories are:
Here is another way to think of these, with respect to proportionality.
For rehabilitation, fully proportionate punishment, i.e., “an eye for an eye,” is the upper limit. The idea again is to inflict the exact same type of pain on a dull but still basically decent or at least reformable person to cause him to realize exactly how he hurt his victim and be horrified by it. If less than proportionate punishment suffices to teach him this lesson, then rehabilitation, and justice on the whole, are well-served.
This type of punishment is an act of charity to the offender and an instance of fraternal correction.
Retribution is an act of fully “deflecting” an unjust attack back onto the criminal. The reaction is opposite and equal to the action; hence a proper retribution will observe perfect proportionality. Or we can say that order is restored when the criminal forsakes his rights to the exact same extent to which he violated his victim’s rights. Unlike rehabilitation, there is no need to hurt in the same way, only with the same amount of suffering.
This signifies not grace and love but personal nature: the criminal is treated according to natural morality but is still regarded as a person.
Deterrence is marked by the fact that some criminals will evade detection and punishment. Purely proportionate punishment will then fail adequately to deter. If 90% of criminals are uncaught, then the punishment to the unlucky 10% must be considerably more severe than a mere eye for an eye, in order to create sufficient threat to the potential future lawbreakers. Their calculations of the profitability of a crime should deter many of them despite a non-zero chance of getting away with the crime.
Thus, punishments to deter will tend to be more than proportionate.
This signifies impersonal nature; the criminal’s happiness is considered, but for all that, he is used as a mere tool for the sake of a separate social good.
Finally, for condemnation, the punishment is in a sense infinite and observes no proportionality at all with the crime. Hell would be the paradigmatic example; but humans can create their own hells, too, through sentences of execution or life imprisonment without possibility of parole. The idea here is that the criminal is totally depraved, and if released would continue his crime spree. He is permanently cut off from society as if a cancerous cell from a body and neutralized thereby.
This is an act of hatred by society of the offender.