Crudely, from the contractarian point of view, the criminal is one who has violated his obligations under the implied "contract" into which citizens enter by virtue of their participation in society. Turnabout being fair play, the obligations of society toward the criminal are likewise nullified by his violation. Now comes the humanitarian crisis: What are we to do with one whom we are no longer obliged to treat as a citizen? History provides scores of apalling answers, but I propose that which is simultaneously most effective and most humane (and most rational, from the contractarian viewpoint), which is simply imposed exclusion from society in general. Note that I do not say "polite society" or "the society of the governed" or "civilized society;" by "society in general" I intend not any particular society but society itself. I mean to say, i.e., that the proper punishment for crime is total isolation from the rest of humanity for a period of time suitable to the severity of the crime: No family, no friends, no guards, no lawyers, no other inmates. No visits, no conversations, no telephone calls, no letters, no e-mails. The cruelty of such treatment is not to be underestimated, and its value over the present penal system, which does not so much exclude the prisoner from society as introduce him to a new one, should be obvious. As a society, prisoners can adapt to the challenge of prison; all that's required for the individual is that he or she learn to play by a new set of rules. Witness here the gang phenomenon. As individuals, however, isolated prisoners are simply shunned. Their only hope for belonging is a return to proper society, and the only means to that end is reconciliation with its rules. Maintaining an environment of monkish isolation for every prisoner of course increases expense, but this could be recovered by releasing consensual criminals (i.e. those convicted of consensual crimes). Prisoners who truly do not understand what civilization requires of them are rare indeed; unwillingness, rather than ignorance, is the rule, and it should be the function of punishment to provide incentive for assimilation by promoting the need to belong.