Tad Homer-Dixon is a rare kind of public intellectual, who combines real expertise with a commitment to communicate to the widest possible readership. In The Ingenuity Gap he wants us all to wake-up to the fearful possibility that our blithe trust in science and technology may be misplaced. Human ingenuity may not be capable of coping with two emerging crises of this century and the next: population growth and environmental despoliation. Read Homer Dixon's wake-up call and you will see the future very differently.

I'm very struck by what you can do in a classroom. I've got 200 students. You don't do partisan politics in a classroom, that's not appropriate. But you want to give them a strong sense that these are the issues that matter.

Political utopias are a form of nostalgia for an imagined past projected onto the future as a wish.

In academic life, false ideas are merely false and useless ones can be fun to play with. In political life, false ideas can ruin the lives of millions and useless ones can waste precious resources. An intellectual's responsibility for his ideas is to follow their consequences wherever they may lead. A politician's responsibility is to master those consequences and prevent them from doing harm. Michael Ignatieff, a former professor at Harvard and contributing writer for the magazine, is a member of Canada's Parliament and deputy leader of the Liberal Party.

One of the greatest feelings in life is the conviction that you have lived the life you wanted to live-with the rough and the smooth, the good and the bad-but yours, shaped by your own choices, and not someone else's.

The wars of the future will be fought by computer technicians and by lawyers and high-altitude specialists, and that may mean war will be increasingly abstract, hard to think about and hard to control.

Living fearlessly is not the same as never being afraid. It's good to be afraid occasionally. Fear is a great teacher.