I am grateful to the University of Aberdeen for the invitation to deliver the Gifford Lectures 2000, which form the basis of this book, and for the warm hospitality provided to a visiting lecturer. I wish to thank also those many authors from whose writings I have learnt and quoted, and especially Faber and Faber for permission to quote from poems by Seamus Heaney and Edwin Muir, and Curtis Brown, on behalf of the Isaiah Berlin Literary Trust, for permission to quote Isaiah Berlin. In addition I acknowledge my debt to other publishers whose failure to answer letters I interpret as tacit permission to quote their authors.

I also want to thank my friend and former colleague, Raymond Barker who, not for the first time, helped me by reading the whole manuscript and making many valuable suggestions.