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 biggest divides in Canada - I said it in 2006, and I said it right through my political career - is urban-rural. Lots of parts of this country feel entirely left behind. And they're mobilized by, you know, the gun control issue.

Mr. Kaplan is the first traveler to take us on a journey to the jagged places where these tectonic plates meet, and his argument--that our future is being shaped far away 'at the ends of the earth'--makes his travelogue pertinent and compelling reading.

Liberals don't want any part of Canada left behind. I used to give speeches on and on and on about the fact that we don't want to have a country where you think, "my kids have got to move to the city if they're going to have any kind of future." We've been saying that, and we've not got through.

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.

The party's got to see itself as being one public service organization in a very competitive field, all of whom are competing for the allegiance and commitment and brains of the next generation. They've got to be big enough to reach out to those groups and say "come on in."

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.