It's in the nature of great surprises in history that you'll always remember where you were when you heard the news.

This is because for most of us most of the time historical and personal experiences don't intersect. We can all see the importance of developments like the collapse of the Soviet Union, or the rise of Islamic fundamentalism, or the emergence of the United States as the most disproportionately powerful state since the Roman empire, but these developments rarely affect the way we get up in the morning, go to work, fall in love, raise families, and grow old. It's hard to see how great events are going to change us, even if it's clear that they're going to change the world. The lives we lead go on pretty much as before regardless of what chapter we've entered, or left behind, in the history of our times.

Every now and then, though, historical and personal trajectories do intersect. What causes them to do so is an event that's sufficiently dramatic in the way it happens, sufficiently sweeping in its implications, and--most of all--sufficiently unexpected, that it causes us all to drop whatever it is we're doing and glue ourselves to the global equivalent of the old town crier, CNN. The distinction between the historical and the personal disappears. Some such events--for example, the Challenger disaster of 1986, the fall of the Berlin Wall in 1989, the death of Princess Diana in 1997, or the Columbia disaster of 2003--hold our attention for a few days, but life then more or less return to normal. The convergence of the historical and the personal turns out to be fleeting. The year in which the event took place may remain in our memory, but the specific date probably will not.

Less frequently, surprises produce more lasting linkages between the historical and the personal. You can tell the difference by how we remember: whether by the year, or by the day. Hardly anyone has forgotten that the assassination of President John F. Kennedy took place on November 22, 1963. The day itself has come to stand for something, so that whatever else may have happened on any of the other November 22nds in history, there's no comparison with this one. The same was true of the attack on Pearl Harbor on December 7, 1941. The everyday lives of everyone changed as a result of that event, so that particular December 7th eclipses all the others. September 11, 2001, before the morning had even ended, attained a similar status in our minds. We all remember what we were doing when we heard the news. And we will remember it all over again, when future September llths roll around for the rest of our lives.

What I will recall about that morning is my frustration at being where I was, although in retrospect I'm not sure where else I would rather have been. With two Yale History Department colleagues, I was just about to begin the PhD oral examination of a brilliant Vietnamese-America student, who with her family had fled South Vietnam a quarter century earlier. This was the most critical moment of all her years in graduate school: we would be deciding, on the basis of her performance during the next two hours, whether she would be allowed to proceed to the writing of a dissertation. We knew only, as she entered the room, that something horrible had happened at the World Trade Center. Because we also knew that our student had family in New York, we agreed to say nothing about this news, for fear of rattling her during the examination.

We were, thus, sequestered from 9:30 to 11:30 A.M., although one or another of us was able to slip out from time to time to pick up scraps of information: that a second plane had crashed into the second tower, that a third had gone down somewhere in Washington, that there were an unknown number of other planes in the air headed for an unknown number of destinations. We did the best we could--while worrying whether our own families, friends, or campus might be one of those destinations--to ask the usual sorts of questions one asks in such exams, and our student, very poised, did fine in answering them. We finally ended the ordeal and sent her out of the room, congratulated ourselves on having kept the news from her, and then called her back in to let her know that that she had passed easily. Only at that point did we tell her what had been happening."Oh, I knew about it," she replied,"but I hadn't wanted to say anything because it might have upset the three of you."

So even though I couldn't be an eyewitness--by way of live television--to the Twin Towers coming down on that dreadful morning, I would not now want to have been anywhere other than where I was. For what my colleagues and I were doing as part of our everyday lives seems to me worth having made the effort to finish up, even as we all knew before we left the examination room that none of our lives would ever be the same. History happens to historians just as it does to everyone else.

Through the days, weeks, and months that followed, most of us--at least those of us fortunate enough not to have lost loved ones or livelihoods as a result of the attacks--managed to return to an approximation of normality. And yet, our understanding of what is"normal" is not what it once was. just as New Yorkers go about their familiar activities in the shadow of an unfamiliar skyline, so something within each of us has also changed. It's as if we were all irradiated, on that morning of September 11, 2001, in such a way as to shift our psychological makeup--the DNA in our minds--with consequences that will not become clear for years to come.

It is, therefore, presumptuous to speculate about those consequences so soon after the event, but it's also necessary. For although the accuracy of historical writing diminishes as it approaches the present--because perspectives are shorter and there are fewer sources to work with than in treatments of the more distant past--the relevance of such writing increases. We act in the present with a view to shaping the future only on the basis of what we know from the past. So we might as well try to know our recent history as best we can, however imperfect the exercise may be. An incomplete map is better than no map at all.

That, then, is what I would like these essays to be: an admittedly premature effort to treat, as history, an event that remains inescapably part of our present--and of our future as well.

Excerpted from Surprise, Security and the American Experience by John Lewis Gaddis, published in September 2004 by Harvard University Press. Copyright C 2004 by The President and Fellows of Harvard College. Used by Permission. All rights reserved.