 It is commonly said that the difference between consequentialist and retributive theories of punishment is that the former is prospective, looking to the good that punishment may accomplish, while the latter is retrospective, seeking to do justice for what a wrongdoer has done. That is a difference between the two, but retributivism should not be reduced to the claim that it is punishment in response to a past crime. Other theories may refer to the fact that wrongdoers have already done something in virtue of which it is proper to punish them without thereby being retributivist. See, e.g., Quinn 1985 (it is rational to threaten people with punishment for crimes, and that rationality is transmitted to punishment if they commit crimes); Tadros 2011 (criminals have a duty to endure punishment to make up for the harm they have caused).