To the Harvard class of 2010: Congratulations on a wonderful achievement. As you reach this milestone, it is fascinating to reflect upon how dramatically the world has changed in just your lifetimes. There have been changes that even the smartest professors that I had at Harvard could not have predicted.

Many of these changes have been for the good. The Soviet Union disintegrated in a Christmas gift to the world, and the Berlin Wall fell without a shot being fired. Former South African President Nelson R. Mandela walked a remarkably peaceful path from prison to the presidency. Peace came to Northern Ireland through the Good Friday Agreement. The light of democracy swept across some of the darkest corners of the globe, and the number of democracies expanded from 69 in 1989 to 119 today. And if you still don’t believe that anything is possible, the New England Patriots won three Super Bowls, the Boston Celtics a National Basketball Association Championship, and the Boston Red Sox not one, but two World Series titles. As for the Bruins—well, we’ll hope for next year.

As positive as many of our advances have been, we have seen catastrophes as well. The tragedy of September 11 and the rise of global terrorism remind us of the fragility of peace in our time. Natural disasters like Hurricane Katrina and the Indian Ocean tsunami demonstrate the abiding power of Mother Nature, even as we burn fossil fuels at rates that put us at grave risk of irreversible climate change. And our recent pullback from an economic abyss shows us the insecurity of our global economic system, which has raised many boats but still leaves over one billion people tragically living on less than $1 per day.

But our technological and scientific breakthroughs have also made possible new solutions to these problems. They are catalyzing educational, economic, and civic-democratic opportunities in previously unimaginable ways. The Internet has revolutionized everything from looking at pictures of your friends to presidential campaigns.

Clearly, you have come of age in a time of both tremendous opportunity and tremendous challenge. To confront these challenges, we need a new approach.

In the wake of President Obama’s election, however, most in Congress looked backward for inspiration. Many Democrats reverted to the New Deal philosophy of former President Franklin D. Roosevelt, Class of 1904, Republicans to the tax cuts and small government philosophy of former President Ronald W. Reagan. One side took refuge in ideas that were 75 years old, the other in ideas that were 30 years old. They are both out of date. They depend on the stale and discredited argument that you must be either for big government or against it, that government is either the solution to all problems or the cause of them.

It would be wiser to listen to President Abraham Lincoln, who said: “The dogmas of the quiet past are inadequate to the stormy present…As our case is new, we must think anew and act anew. We must disenthrall ourselves, and then we shall save our country.”

Our stormy present requires citizen activism. We shouldn’t look to big government or big business to create the solutions we need, but rather to big citizenship and a renewed sense of common purpose.

Big citizenship means contributing to a cause larger than your own self-interest. It calls on each and every one of us to perform community service, to get involved in politics, and to join with other citizens in larger movements for change.

It says we need to foster innovation and entrepreneurship in the public, private, and non-profit sectors to develop the new ideas and solutions we need to address the new problems we face.

Big citizenship calls on us to define a new catalytic and transparent role for government, one that ensures a level playing field, monitors performance, uses competition and choice, and rewards and scales up what works while recognizing and shutting down what doesn’t.

Big citizenship recognizes that we should forge public-private partnerships among all three sectors that can leverage the strengths of each to address our most pressing challenges.

Most of all, a new philosophy of big citizenship and common purpose demands that we move away from the old, misguided question of “Are you better off?” to the real question: “Are we better off?” We must reassert the spirit of our founding fathers and mothers who “mutually pledged their lives, fortunes and sacred honor”—the spirit that we are all in this together.

You all, as Harvard students, have already demonstrated your commitment to service on campus. You have volunteered in record numbers through the Phillips Brooks House Association, you have found summer jobs through the Center for Public Interest Careers, and a record 14 percent of you applied to work for Teach for America.

Now, as you prepare to head out into the real world to create extraordinary lives, I hope you will continue to nurture that spirit of service in assuming what former President Harry S. Truman called the “highest office” in the land: that of citizen. It will be up to your generation, the first of the 21st century, to define and shape the new approach that will help us overcome the challenges and seize the opportunities of our times. So congratulations and carpe diem; the world both needs you and awaits.

Alan A. Khazei ’83 graduated from Harvard Law School in 1987, is the co-founder of City Year, and the founder and CEO of Be The Change, Inc.