The real lesson of 9/11 that I think we have still to learn is that this is a world of interdependence, in which all of the challenges of environment and climate change, of jobs, of disease, of war and terrorism, are cross-border problems that cannot be met one nation at a time.

Civility is a work of the imagination, for it is through the imagination that we render others sufficiently like ourselves for them to become subjects of tolerance and respect, if not always affection.

By the laws of the land, people who come looking for jobs in America are illegal. But by the laws of economics, they are following the logic and laws of economics when they leave Guatemala and go to Mexico, leave Mexico and come to the U.S., leave Africa and go to Spain and Europe looking for jobs.

I divide the word into learners and nonlearners. There are people who learn, who are open to what happens around them, who listen, who hear the lessons. When they do something stupid, they don't do it again. And when they do something that works a little bit, they do it even better and harder the next time. The question to ask is not whether you are a success or a failure, but whether you are a learner or a nonlearner.

When it comes to acid rain or oil spills or depleted fisheries or tainted groundwater or fluorocarbon propellants or radiation leaks or sexually transmitted diseases, national frontiers are simple irrelevant. Toxins don't stop for customs inspections and microbes don't carry passports. North America became a water and free-trade zone long before NAFTA loosened up the market in goods.

I divide the world into learners and non-learners.

Where once the student was taught that the unexamined life was not worth living, he is now taught that the profitably lived life is not worth examining.