In this work, I owe a special debt to two colleagues. Raymond J. Lasek, from whom I learned biology, always provided a thoughtful, challenging, and critical response as I presented him with various steps in my thinking out of these ideas. Ulf Grenander was my warm and generous host in the Division of Applied Mathematics at Brown University. His Pattern Theory is the language that I have borrowed in an attempt to formalize my ideas about templeting. A language is more than a tool, it structures one's thoughts; and Prof. Grenander's language is responsible for much of the organization of my ideas. Both of these scientists engaged me in innumerable hours of epistemological discussion, and I cannot help but to have adopted many of their good ideas. Some of these are now woven inextricably throughout this book.

I would also like to thank the Alfred P. Sloan Foundation and the Whitehall Foundation, which provided financial support for this work.

The title of Chapter 2 is borrowed whole from the book The Nature Of Explanation in which the author, Kenneth Craik, makes a strong case for the importance of determinate explanations.

The story that I present in this book is not as tidy as I had originally hoped, but I think that this is the nature of detailed abstractions that must be tethered to the real world.