In the course of writing this book I came to owe a great deal to various friends and colleagues. In particular I wish to thank Rees Davies of University College, Aberystwyth, David Dumville of Cambridge University and Harry Dickinson of the University of Edinburgh for the time they gave to reading various portions of the typescript. I am especially grateful to the Master and Fellows of Peterhouse, Cambridge, and to the Governing Body of the University of Wales, who awarded me visiting fellowships in 1985. My stay in Aberystwyth was made particularly enjoyable thanks to the hospitality of Rees Davies, Gareth Williams, John Davidson, Martin Fitzpatrick and their wives. I wish also to express my gratitude to the University of Pittsburgh for granting me leave of absence during the Fall Term, 1985. At various times, I benefited from the encouragement of Janelle Greenberg of the University of Pittsburgh, John Pocock of Johns Hopkins University, Joseph Lee of University College, Cork, James Shiel of the University of Sussex and Lord Dacre of Glanton, erstwhile Master of Peterhouse. Brian Wormald, my friend and old supervisor at Peterhouse (1942–3), gave me many hours of his time forty years later. James Shiel provided the epigraph. Like many others I have incurred a debt to Linda Randall, Hazel Dunn and Maureen Ashby. Mr William Davies of Cambridge University Press has displayed patience and sympathy beyond the call of duty.