The Cambridge University Press first suggested to David Lewis in 1987 that it might publish a book of his. He gladly agreed to the publication of a volume of his selected papers, and started to think, and to consult friends, about what ought to be included in it, but he did not come to a final decision on the contents. Shortly before his death, in 1994, he asked me as his literary executor to take the final decision (which I have done after further consultation) and to edit the book.

Chapters 5, 21, 25 and 26 are published here for the first time. They are the papers from amongst his unpublished works which Lewis wanted to be included in this volume. He did some work on them in the last year of his life, but he left it to me to do the final editing, and to write the footnotes (though he gave some indication of what he wanted, and in some of the notes which provide more than bare references I have been able to use his words). Copies of some other unpublished papers are being deposited in selected libraries: see p. 411.

The remaining chapters have been published before, and I am grateful to the editors and publishers concerned for permission to republish them here. I have standardised the form and have done some updating of the references; I have supplied a first footnote (cued by an asterisk rather than by a number) for each chapter, including the details of its first publication; my more substantial interventions elsewhere are enclosed in square brackets.