The research for this book was made possible by two periods of research leave from Aberystwyth University. I was fortunate in being granted membership of the Institute for Advanced Study, Princeton, and a visiting fellowship at Wolfson College Cambridge, which enabled me to benefit from the rich research resources of each. My thanks to all of them.
Among the many people with whom I have profitably discussed my work, particular thanks are due to Leslie Armour, Stephen Clucas, Alan Gabbey, John Rogers, and Ann Thomson, as well as to Mark Burden, Guido Giglioni, John Henry, Richard Serjeantson, and M. A. Stewart for sharing their expertise with me. I also thank Dawn Goldstone for editorial assistance.
I am grateful also for the constructive comments of the referees on earlier drafts of the book, and for the patience and helpfulness of the Oxford University Press philosophy editor, Peter Momtchiloff.
Sarah Hutton