I am greatly indebted to Maurice Salles for kindly allowing me to use our joint article of 1981 as the basis for this monograph. My sincere thanks go to Amartya Sen both for numerous incisive comments and suggestions which he made on previous versions of the manuscript and for his continual encouragement. Extensive discussions, both orally and in written form, with Nick Baigent, Graciela Chichilnisky, Keith Dowding, Bill Gehrlein, Charles Horvath, Michel Le Breton, Andreu Mas-Colell, Eric Maskin, Iain McLean, John Weymark and Myrna Wooders are also gratefully acknowledged. Many thanks to Brigitte Arnold for patiently producing various versions of the manuscript. As a result of the hospitality of STICERD at the London School of Economics, the final revision could be prepared in a very stimulating and friendly environment. Last but not least, I wish to thank both Deutsche Forschungsgemeinschaft and Volkswagen-Stiftung for their generous financial support at various stages during my research.

Barbara Docherty, Chris Harrison and Michelle Williams of Cambridge University Press were very helpful during the production of this book.