If someone has already been mistakenly punished for a crime they have not committed, are they then allowed to go and commit that crime (without punishment)? For example, supposing person A is charged with the murder of B but wrongly so as B was still alive. Does A then have the right, once he's finished his sentence in jail, to go and kill B? He has already been punished for it so you can't punish him twice for the same act!!

No, of course not! ...or so I first thought; but then your argument moved me; but now I again think...
No, of course not!

A's first punishment was probably unjust--certainly unfortunate. But if A now kills B, then A should be punished anew on any of the four halfway-plausible and at-least-sometimes-applicable justifications for punishment that I can think of.

Deterrence: If we don't punish A anew, then we'll experience a crime-wave of similarly pardoned ex-cons (assuming certain ugly things about human nature).

Rehabilitation: Well, incarceration didn't exactly work any criminal tendencies out of A, did it? (And it doesn't generally seem to accomplish much rehabilitation, at least in the U.S..) But if incarceration would promote rehabilitation, which A surely needs, then A should be incarcerated.

Public safety: Things didn't go so well when A was let out, so we're all better off keeping him in the slammer.

Retribution: Here's where your argument has some force. If the score for B's death is properly settled by a certain punishment of A, then why does it matter when this punishment takes place? A punishment delayed is not a punishment denied, so why not one ahead of time? If it's eye for an eye, does it matters which gets poked out first?

The retributivist might say that we need to distinguish carefully between the different killings of B, actual and merely possible. A's first punishment was for one (supposedly by poison) that didn't take place, but that can't be used to settle a different killing--the one that actually took place (by shooting). But this doesn't seem so convincing, particularly if you think of different types of punishments, like fines. Why can't I apply my credit for the fine the IRS now admits I needn't have paid to the fine it might charge me if it audits the bogus tax-return I'm about to send in? (Although here there's the possibility of applying the credit to something other than a potential fine, like a better tax accountant; but the years poor A lost during the first punishment can't now be spent in some other way.)

The retributivist might also say that retribution requires that the punished suffer the punishment knowing that the punishment is for a certain crime. I'm not sure, though, that retribution is always thought to work this way (consider trans-generational retribution); and in any case, you can easily concoct cases where the criminal knows exactly what crime s/he wants to commit (and exactly when), and then calculates that it's more efficient to pay the price ahead of time.

The retributivist might also say that a punishment can't really count as retribution--as a making of amends--if it happens before the crime. But this seems just to answer your question by stipulation.

Finally, the retributivist might just bite the bullet: in so far as punishment is about retribution, then A has, in fact, pre-paid for the killing of B. That's what I think the retributivist should say.

So...Nice argument. And so much the worse for retributivism. Good thing we needn't hold that justified punishment is entirely about retribution. Good thing I don't think any is: it's not clear to me that retribution promises to improve the world's future in any way. And even when--especially when--it comes to punishment, we have to move on.

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