The optimist underestimates how difficult it is to achieve real change, believing that anything is possible and it's possible now. Only by confronting head-on the reality that all progress is going to be obstructed by vested interests and corrupted by human venality can we create realistic programmes that actually have a chance of success.

If philosophy is to be a valuable part of life, we have to appreciate it for its own sake, and not just for what it's done for us lately.

There are many things you shouldn't measure. Don't, for example, try to measure how much you love your wife!

I never thought I was cut out for a life of crime. I even felt guilty when I accidentally stole a Subbuteo catalogue, thinking it was free. But everyone has an inner rebel, and mine has finally found a natural outlet. My crime of choice is that, with a heart as cold as ice and no care for what society thinks, I steal wireless computer network time.

Progress is more of a challenge for the cynic but also more important and urgent, since for the optimist things aren't that bad and are bound to get better anyway.

Once Steve Fuller said that there is this idea that your responsibility as an intellectual is just to speak the truth as you see it. But actually, you should be more appreciative of what needs to be said. I don't think that's ever an excuse to say something you don't believe is true - but sometimes the emphasis has to be different. Well, if I'm talking to an audience of hardline atheists, I'll be trying to unsettle them a bit more, whereas, if I'm speaking to an audience of believers, I'll be giving them more of the pros of atheism. It's about having a sensitivity to context.

The very act of questioning whether you exist proves you do, because you must be there for the doubt to be entertained in the first place.