Book excerpt: In the first two volumes of On What Matters Derek Parfit argues that there are objective moral truths, and other normative truths about what we have reasons to believe, and to want, and to do. He thus challenges a view of the role of reason in action that can be traced back to David Hume, and is widely assumed to be correct, not only by philosophers but also by economists. In defending his view, Parfit argues that if there are no objective normative truths, nihilism follows, and nothing matters. He criticizes, often forcefully, many leading contemporary philosophers working on the nature of ethics, including Simon Blackburn, Stephen Darwall, Allen Gibbard, Frank Jackson, Peter Railton, Mark Schroeder, Michael Smith, and Sharon Street. Does Anything Really Matter? gives these philosophers an opportunity to respond to Parfit's criticisms, and includes essays on Parfit's views by Richard Chappell, Andrew Huddleston, Katarzyna de Lazari-Radek and Peter Singer, Bruce Russell, and Larry Temkin. A third volume of On What Matters, in which Parfit engages with his critics and breaks new ground in finding significant agreement between his own views and theirs, is appearing as a separate companion volume.