Many friends and colleagues have helped me by reading and commenting on material which has found its way into this book. But I am especially indebted to David Burrell, CSC, James Claffey, OP, John Marenbon, James McEvoy, Simon Tugwell, OP, Christopher Williams, and Mark Wynn. I must also thank Hilary O'Shea for being a most gracious and encouraging OUP editor. Over many years Herbert McCabe, OP has taught me more about Aquinas than I can now remember. Perhaps it is true that, in the language of Aquinas, he is the most significant secondary cause of my text. He will not like it. But that is only to be expected.