A few months ago I published a book about the history of the death penalty in the United States. Ever since, whenever something relating to the death penalty takes place (a court decision, an execution, etc.), I get calls from journalists looking for quotes. My normal response is something like "yes, that's the way things have been happening for some time," or "that reminds me of such-and-such case." But that's never the kind of quote the reporters are looking for. "That's very interesting," they'll say, even though they don't really think it is, "but . . ." and what comes next is a request for some kind of prediction. Will this defendant get the death penalty? Will other governors do what this governor did? Will the event that occurred today be part of a broader trend? What's going to happen next?

My initial reaction is always the same: How am I supposed to know? I've learned a lot about the history of the death penalty, but I haven't learned a single thing about its future. Why should I be expected to make better predictions than anyone else?

At first I attributed these questions to a combination of journalistic convention and an overestimation of my expertise. On one hand, there seems to be a custom that newspaper stories aren't complete if they just describe what happened; evidently they must also include quotations from people explaining what it all means for the future. And on the other, journalists are like lots of people in believing that professors are smarter than they actually are. Put these things together, and it makes perfect sense to get the predictions from someone who knows something about the history of a subject. He wrote a book, a journalist might think, so he must know what's going to happen next. Or at least he'll have a better guess than other people I might call.

But lately I've been wondering whether there's more to it than that. When people ask for predictions, maybe they're proceeding on the basis of a tacit theory of history, a theory they may never have brought to the level of articulation. Sometimes I get the feeling that I'm being expected to use the past as a source of data from which I'm supposed to identify a trend that will continue to move in the same direction in the future. Over the past two centuries, for example, Americans have gradually reduced the number of crimes that carry the death sentence. Doesn't this mean, people ask, that we'll soon abolish the death penalty for murder too? In the past, in cases involving black defendants and white victims, there was sometimes a thin line between a lynching and an official trial and execution. Shouldn't we expect that to be true of racially charged cases in the future? On this view of history, the way things have gone is the way we should expect them to continue going. Knowledge of the past helps us predict the future. If that's true, then historians are the best people to ask for predictions.

It wouldn't be surprising if that's the way people think about history, because we see that kind of thinking in many areas of life. People put their money into the stock market after it has gone up for a while, and take their money out after it has gone down, behavior that would be silly unless one expects the past to be a good predictor of the future. Participants in social movements often have a sense that they're being carried along by events that would happen even without their help. Early communism was an extreme example, but even so non-extreme a group as opponents of the death penalty tend to speak of inexorably evolving standards of decency with which judges and legislators ought to keep up. The direction of change in the past, they implicitly believe, will also be the direction of change in the future.

Is that the right way to think about history? Professional money managers, the sort of people who handle university endowments, don't buy stock after the market has gone up. They buy it after the market has gone down, because that's when it's cheapest. In their view, the direction of change in the past provides no information at all about the direction of change in the future. Some trends will continue, others will not, and there is no way to know in advance which is which. Opponents of the death penalty were more confident about the inexorable movement away from capital punishment in the early 1970s than they were in the late 1980s, after evolving standards of decency switched direction and began evolving toward more executions. Sometimes surprising things happen. If that's the right way to think about history, then historians won't be any better at predicting the future than anyone else.

In fact, historians might even be worse. The more one knows about the past, the more one might expect the future to look just the same. If there is any academic discipline whose members one might expect to systematically underestimate the likelihood of change in the future, it is History. Maybe knowing a lot about the past is actually a bad thing when it comes to predicting the future.

Knowledge is liberating, sometimes. But sometimes it can be confining as well. Lawyers tend to see things as legal issues, engineers as engineering issues, and so on. Maybe historians are occupationally prone to imagining that the future will look like the past. If so, then they're the last people we should be asking to make predictions.

There's no way to know, because no one keeps track. As Richard Posner recently pointed out in his book Public Intellectuals, academics (including historians) are free to say anything they like about the future without fear of being exposed as charlatans, because when the future comes no one will check to see if they were right.

So what do I do when I'm asked to predict the future of the death penalty based on its past? I could decline, and modestly explain that I don't know any more about the future than anyone else. That's not what I do. I could say "what the heck, everyone else does it," and pretend I know what I'm talking about. I don't do that either. Instead I'm in the middle. I respond with absurdly long and ambiguous conditional predictions. If A keeps going the way it has been going, and if B doesn't happen, and if C occurs before D, then E is probably more likely than F. I can't recommend this as a strategy for anyone aspiring to be quoted in the newspaper. My predictions tend to elicit long silences on the other end of the phone, followed by polite inquiries as to whether I know of anyone else qualified to speak on the matter. But I hope Richard Posner will take note: I haven't been wrong yet.