For me philosophy begins with these experiences of disappointment: a disappointment at the level of what I would think of as "meaning," namely that, given that there is no God, what is the meaning of life? And, given that we live in an unjust world, how are we to bring about justice?

Now, if laughter is proper to the human being, then the human being who does not laugh invites the charge of inhumanity, or at least makes us somewhat suspicious.

We must believe, but we can't believe. Perhaps this is the tragedy that some of us see in Obama: a change we can believe in and the crushing realisation that nothing will change.

In relation to the question of hope, I think the only hope we have is hope against hope. We hope for a better world. But of course we can do better than just hope.

I have argued that philosophy doesn't begin in wonder or in the fact that things are, it begins in a realization that things are not what they might be. It begins with a sense of a lack, of something missing, and that provokes a series of questions.

The thing about humour is that the super-ego is also at play, so what interested me, particularly in the last chapter which is key to the book -and no one seems to have picked this up in writings on Freud - is that, in the later Freud, the essence of humour is the ability to look at myself and find myself ridiculous. That makes me laugh.

Genuinely great humour recognises the world it's describing and yet we are also called into question by it. That's what great art should do. That's what great philosophy should do. The one thing about humour is that this is an everyday practice that does this.