This book is a collection of related but independent essays. Such books are notoriously hard to classify-a fact that alarms me, since they thereby become hard to shelve, review, and sell. And so I imagined, when I first conceived the idea of collecting them, that I would have to devote some considerable effort to finding a Common Theme that they all illustrate or contribute to, and thereby show that theyhave better reason to congregate between one pair of covers than the simple fact that I wrote them. It quickly turned out, though, that no great effort was required. These essays, although written over a period of about twenty-five years, and in widely varying circumstances, fit together and support each other so well that I can only suspect my subconscious of having planned them as chapters of one book from the start. I have had to discipline myself, in fact, to hold to a reasonable number the cross references that I inserted whenever I found that a point I try to make in one chapter is supported or amplified by an argument offered in another. The problem has been not to find their common theme, but to retain some autonomy for the several essays the book comprises.
