This book essentially takes the form of an extended essay. I have divided it up into sections, rather than formal chapters, in order to develop the flow of the arguments in an uninterrupted fashion. The ideas expressed herein are directly bound up with my previous writings, and I have often made reference to these, I hope the reader will understand and forgive such frequent self-referencing, which is intended not as hubris but as a mode of providing backing for claims that cannot be exhaustively defended in a work of this brevity. The book began life in the shape of the Raymond Fred West Memorial Lectures, which I delivered at Stanford University, California, in April 1988.1 am very grateful to my hosts at Stanford on that occasion, whose welcome and hospitality was wonderful. In particular, I am indebted to Grant Barnes, of Stanford University Press, who was instrumental in gaining me the invitation to give the lectures and without whom this work would not exist.