These essays have developed out of a number of ideas which I began to sort out during a semester at Cornell in 1963-64, but which were not finally reduced to their present form until early in 1966. During that time, the inflation had accelerated to such an extent that it was becoming impossible to treat the later stages as fully as I would have liked. Consequently my emphasis may seem a little lopsidedly concentrated on the earlier years rather than on more recent developments. However, I do not think the main outlines of my argument are seriously weakened for that reason, since the lessons...