Cynthia Macdonald is Professor of Philosophy at Queen's University Belfast and Adjunct Professor of Philosophy at the University of Canterbury, New Zealand. Her previous publications include Mind-Body Identity Theories (1989), Varieties of Things: Foundations of Contemporary Metaphysics (Blackwell, 2005), and she is co-editor, with Stephen Laurence, of Contemporary Readings in the Foundations of Metaphysics (Blackwell, 1998). Graham Macdonald is Professor of Philosophy at the University of Canterbury, New Zealand, and Distinguished International Fellow at the Institute of Cognition and Culture, Queen's University Belfast. He is co-author, with Philip Pettit, of Semantics and Social Science (1980). In addition, he is editor of Perception and Identity: Essays Presented to A. J. Ayer, with His Replies to Them (1979), co-editor, with Crispin Wright, of Fact, Science, and Morality (Blackwell, 1986), and co-editor, with Philip Catton, of Karl Popper: Critical Appraisals (2004). Together, they have edited Philosophy of Psychology: Debates on Psychological Explanation and Connectionism: Debates on Psychological Explanation (both Blackwell, 1995).