Having been given this space by the editors, I want first of all to thank Ian Carter and Mario Ricciardi most warmly for their idea of this volume – a total surprise for me – and for having realized it in so stimulating a way. I am also very grateful to all the contributors who have provided so much food for thought. A number of them have chosen to deal specifically with topics which have been of concern to me in my own writings and developed them in new directions. This gives me a welcome opportunity for re-examination and clarification.