Andrew Sepielli in Notre Dame Philosophical Reviews:
This is a volume of essays on meta-ethical themes from Derek Parfit's magisterial book On What Matters. It boasts an impressive list of contributors, most of whom, we learn from Peter Singer's introduction, were chosen because Parfit saw fit to criticize their views at length. Predictably, then, most of them are established "big names", and many of their essays are defensive in character. As a result, the volume is a bit too intellectually conservative to meet the editor's stated goal of "reinvigorat[ing] discussions of objectivism in ethics". Nonetheless, it helps to clarify these discussions, and to bring out the deeper concerns that animated Parfit's bold and at times controversial stances in meta-ethics.
Several of the essays respond to Parfit's arguments against moral naturalism — in particular, his contention that if naturalism were true, moral claims could not state substantive truths. Now, we may agree with Parfit when it comes to crude versions of analytical naturalism, on which "is right", say, simply means "maximizes happiness". But Parfit means to target what he calls "non-analytical" naturalism as well, for he regards triviality as a metaphysical rather than a conceptual matter: no moral claim is substantive unless it ascribes an "irreducibly normative property". Since the naturalist does not believe in such properties, she must either say that moral claims are false (if, as Parfit suspects, they ascribe irreducibly normative properties), or non-substantive (if they don't).
A striking set of claims. Where do the contributors think it goes wrong? Peter Railton's essay is the one most squarely devoted to this question. He offers an alternative, naturalism-compatible account of substantivity.