Mark Timmons is Professor of Philosophy at the University of Arizona. He is author of Morality without Foundations (OUP, 1999), editor of Kant's Metaphysics of Morals: Interpretative Essays (OUP, 2002), co-editor of Metaethics After Moore (OUP, 2006), and of Kant on Practical Justification (OUP, 2013), and editor of Oxford Studies in Normative Ethics, published annually. ; Robert Johnson is Professor of Philosophy and Chair of the Philosophy Department at the University of Missouri, Columbia. Johnson's PhD dissertation was written under the supervision Thomas E. Hill, Jr. at UNC Chapel Hill in the late 1980s and early 1990s.