Some externalities involve only a few uncompensated losers of rights whose costs are easily reckoned in monetary terms, so that forcing the taker to pay exactly these costs to the victims ensures both that victims will be fairly compensated and that takers will take rights only where they value the rights more than the losers do. The law calls these externalities torts, and the same principle of liability pricing extends to crimes, in which, with the same unlawful act, someone simultaneously takes the rights of many people who suffer moral costs that can't be satisfactorily measured by money. As with torts, some crimes may be efficient reallocations of rights, and the logic of liability shows that proportional punishment can, ideally, discover which crimes are or are not efficient and force all takers to compensate their victims in full for what they take.