On What Matters is a major work in moral philosophy. It is the long-awaited follow-up to Derek Parfit's 1984 book Reasons and Persons, one of the landmarks of twentieth-century philosophy. In this first volume Parfit presents a powerful new treatment of reasons and rationality, and a critical examination of three systematic moral theories -- Kant's ethics, contractualism, and consequentialism -- leading to his own ground-breaking synthetic conclusion. Along the way he discusses a wide range of moral issues, such as the significance of consent, treating people as a means rather than an end, and free will and responsibility. On What Matters is already the most-discussed work in moral philosophy: its publication is likely to establish it as a modern classic which everyone working on moral philosophy will have to read, and which many others will turn to for stimulation and illumination.

"Review from previous edition an epochal work ... Parfit's intellectual personality radiates throughout On What Matters, which as a whole presents a gripping and illuminating picture of a single, comprehensive view of the projects of both normative and metaethical inquiry." - Mark Schroeder, Notre Dame Philosophical Reviews

"the most significant work in ethics since Sidgwick's masterpiece was published in 1873 ... a work of epic proportions and ambitions." - Peter Singer, Times Literary Supplement

"Parfit's intricate and beautifully lucid book is undoubtedly the work of a philosophical genius." - John Cottingham, The Tablet