h i s b o o k w a s written at the Center for Advanced Study in the Behavioral Sciences, on a grant partially funded by the National Endowment for the Humanities. Over the years, those who staff the Center have perfected a happy combination of solicitude and benign neglect, and I find myself deeply in their debt. In particular, I am indebted to Virginia Heaton for her invaluable services as typist and proofreader. My research assistants at the University of Rochester—Everett Akam, Ken Hawkins, Chris Lehmann, and Colin Morris—have given me many reasons to be thankful. Ian Shapiro, Nell Lasch, and Chris Lehmann read the entire manuscript, proving, if nothing else, that such a thing was possible; they also offered advice, most of which I have reluctantly had to follow. Dan Borus, David Chappell, Dale Vree, Stewart Weaver, Robb Westbrook, and Suzanne Wolk read portions of the manuscript, and I am grateful to them as well, for advice and especially for encouragement. At a time when I was groping for a title, Jim Campbell suggested a rereading of "The Celestial Railroad." Jeanette Hopkins edited the manuscript very thoroughly, not to say aggressively; her innumerable recommendations, even when I turned them down, often had the effect of calling attention to some difficulty that required revision.

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