When, in the immediate aftermath of Sept. 11, 2001, Yale President Richard Levin asked us to organize the lecture-discussion series we called “Democracy, Security and Justice: Perspectives on the American Future,” neither we nor anyone else could be sure what that future might be.

Because the attacks on New York and Washington brought to mind the one on Pearl Harbor 60 years earlier, it seemed reasonable to expect that we’d be at war and that everything would be different. A year later we are at war, but for those of us fortunate enough not to have lost loved ones or livelihoods, life is much the same.

Nobody’s been drafted, our campus hasn’t been turned into a military training camp, it’s still possible to travel freely around the country, indeed around the world. The only visible reminders of Sept. 11 most of us encounter are the heightened security checks at airports and an altered New York skyline. Like those in the city beneath that skyline, we’ve resumed our normal lives, something none of us could have been confident about when we picked up our copies of the Yale Daily News on the morning of Sept. 12, 2001.

And yet, like the New York skyline, not everything is the same. There’s been a shift in consciousness — a rearrangement of mental DNA — that’s left everyone who experienced Sept. 11 with the sense that life can never again be quite what it once was. We’ve all had to reassess our strengths and weaknesses, how we look at others, what we value in ourselves. Familiarity coexists now, with strangeness, and we’re having to adjust. The Democracy, Security and Justice series, we hope, facilitated that process here at Yale, and in our capacity as organizers we’d like to thank everyone who participated. We learned from you.

And what was it we learned? If we had to sum it up in a single sentence, it would be this: “Don’t take for granted important things.”

Don’t take for granted, first, safety because we live in a dangerous world made more dangerous by what Sept. 11 showed about the vulnerability of so many to the malice of so few.

Don’t take for granted patriotism — in whichever nation it may reside — for states and the people that support them still offer the best protection against these dangers.

Don’t take for granted tolerance and the civility it produces because these qualities aren’t encoded in human nature. They have to be taught and they must be learned.

Don’t take for granted this place, and the others like it, in which teaching and learning happens.

Don’t take for granted standards — whether of ethics or excellence — for without them what is the point of teaching?

Don’t take for granted faith, for without it where is the hope that fuels learning?

Don’t take for granted love, for life is short.

This Sept. 11, like all the others that lie ahead, will be a day to mourn the dead, to relive memories, and to reflect on their meaning. We hope the events taking place at Yale and elsewhere will also establish it as a day of reaffirmation: as an annual reminder not to take for granted all that was threatened on a day we’d all like to forget, but must always remember.

John Lewis Gaddis is the Robert A. Lovett Professor of Military and Naval History. Cynthia Farrar is a lecturer in political science and the director of urban academic initiatives.