Much of the work on this book was done during my tenure of a Leverhulme Major Research Fellowship: I am very grateful to the Leverhulme Trust for this award, which gave me three invaluable years free from teaching and administration in which to think again about some of the questions on which I had been working for a number of years, and to make effectively a fresh start. I am also grateful to the University of Stirling for the support I have received, not just during the writing of this book, but throughout my academic career; and especially to my colleagues in the Department of Philosophy, who (apart from offering helpful comments on many aspects of the book) have through the years provided an ideally collegial, friendly, enthusiastic and constructively critical environment in which to pursue research.