I've been teaching capital punishment for the last week in my ethics class. There are two main arguments for the death penalty, and I see them as relatively independent of each other. Retributivism is the view that the death penalty is the only just punishment for premeditated murder because it is the only punishment that's proportional to the crime. A life was taken, and that is so serious that no other punishment matches up with what the murderer deserves. This sort of argument rarely occurs in public policy arguments, in my experience, even though it's the argument with much stronger philosophical support historically. I think that's probably because our culture has moved away from liking the idea that we deserve anything bad when we do wrong. Most people do accept a kind of retributivist justice when they get robbed of something they think they've earned. They just don't want to extend retributivist arguments against wrongdoing.
So death penalty advocates have often relied on deterrence claims in recent decades. The only problem is that studies aiming to establish whether capital punishment deters any potential murderers from killing have been fully inconclusive. The ones with the strongest conclusions have tended to be the ones with the least credibility. The weaker the conclusion, the fewer problems critics have been able to find. This is so in both directions, and many people familiar with the literature have concluded that we can't know whether capital punishment deters, and that has left philosophers defending the death penalty trying to establish why we should retain capital punishment even if we can't show that it deters. A couple of those arguments are, I think, quite brilliant. One takes a form of Pascalian-style wagering based on the potential rewards if you bet on deterrence and win vs. if you bet on it and lost, compared with what happens if you bet on non-deterrence and ban capital punishment. There are difficulties with these arguments, but I find it fascinating that people would go to such lengths to defend the deterrence value of capital punishment because studies on deterrence are inconclusive, when the historic justification for the death penalty doesn't assume any deterrence at all.
That was the state of play a few years ago. It's pretty much how all the ethics books dealing with the question leave things. It amazed me, therefore, to see that The New York Times highlighted a dozen studies in the last few years that conclude that the death penalty does deter murders, from as many as 3 to 18 murders per execution. This article was published in November. I only heard about it because Joe Carter linked to it. I didn't save a link to it at the time and had to do some careful Google searching just to located it again. I didn't see other reports of it in that searching.
That surprises me, because this is huge if these studies turn out to be well-founded. It changes the whole debate about the second justification for the death penalty, and apparently it's changed the minds of a number of important figures, including Cass Sunstein, a well-left-of-center law professor who had been completely opposed to the death penalty. I haven't seen these studies, and I'm not sure I'm qualified to evaluate them fully even if I did see them, but I do know some people have criticized them, although that tells us very little. Some people will criticize anything that gives a conclusion they don't like. I'm going to be looking out for further developments on this. I don't think those who support the death penalty should abandon retributivism, but if the death penalty does deter that's worth knowing about, because those who aren't retributivists might be basing their whole evaluation of the death penalty on this one question.