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