Now that I have rejected Kant's theory of retribution on the basis of a liberal interpretation of his concept of right in favor of a combination of specific deterrence and rehabilitation, I would like to investigate whether the alternative, stronger or moral interpretation of his concept of right can substantiate Kant's theory of retaliation. As was shown in the first chapter, this interpretation consists of an implementation of the categorical imperative in the legal system so far as the commands and prohibitions of the categorical imperative are able to be implemented by force.

Which type of moral proportionality is at issue?

The current retributivist theories of punishment often radically differ from Kant's own theory because they assume that punishment is justified by a goal, however modest this goal may be. The position held by expressivists, for instance, states that punishment should be seen retributively so that society's moral judgment about the punishable action can be expressed. Another theory of punishment, such as the one held by Jean Hampton and Jeffrie Murphy, regards the punishable action as comprised of the criminal putting his or her value over the worth of the victim. The retributive punishment that is then stipulated is a punishment that restores the proper relation between the worth of the victim and the worth of the criminal.

In opposition to such theories as well as similar ones, and also against the legal tradition following Seneca's dictum (as I have mentioned before), “nemo prudens punit quia peccatum est sed ne peccetur,” is Kant's view, according to which the punishment should not be allowed to have a goal (Zweck) but rather should be inflicted only “because of his having committed a crime.”