This book is rooted in my 1998 doctoral dissertation, written at the University of Massachusetts, Amherst: “Natural-Kind Term Reference and the Discovery of Essence.” Roughly half of the chapters in the book (Chapters 2-4) have ancestors in the dissertation, though these chapters have all been extensively revised. Half of the chapters in the book (1, 5, and 6) are essentially new.

Because I outline the contents of this book in an Introduction, I will not do that here, too. Instead, I would like to express gratitude to many people and institutions for their support of this book. My dissertation director, Bruce Aune, is first on my list of those to whom I owe thanks. Bruce did much, both by criticism and by encouragement, to help to shepherd my dissertation to completion. I am very grateful for this philosophical and personal assistance and for the valuable help that Bruce has continued to provide since my graduate school days. Of particular relevance here is Bruce's trusted reaction to much of the newer material in this book. I owe much of whatever success the book enjoys to Bruce.

I am grateful to other members of my dissertation committee as well. Lynne Rudder Baker has offered highly valuable help and advice on the dissertation and much more. I am most grateful to her. Fred Feldman was a source of helpful feedback. I discussed some of the biology with James Walker, a biological systematist serving as the outside member of the committee.