Derek Parfit, who died in 2017, is widely believed to have been the most significant moral philosopher in well over a century. The twenty-one new essays in this book have all been inspired by his work. They address issues with which he was concerned in his writing, particularly in his seminal contribution to moral philosophy, Reasons and Persons (OUP, 1984). Rather than simply commenting on his work, these essays attempt to make further progress with issues, both moral and prudential, that Parfit believed matter to our lives: issues concerned with how we ought to live, and what we have most reason to do. Topics covered in the book include the nature of personal identity, the basis of self-interested concern about the future, the rationality of our attitudes toward time, what it is for a life to go well or badly, how to evaluate moral theories, the nature of reasons for action, the aggregation of value, how benefits and harms should be distributed among people, and what degree of sacrifice morality requires us to make for the sake of others. These include some of the most important questions of normative ethical theory, as well as fundamental questions about the metaphysics of personhood and personal identity, and the ways in which the answers to these questions bear on what it is rational and moral for us to do.

He demonstrates that a broad parallelism exists between developments in ethical theory among Continental philosophers of the phenomenological persuasion and the more analytically inclined philosophers of the English-speaking world.

Derek Parfit, who died in 2017, is widely believed to have been the best moral philosopher in well over a century. The twenty new essays in this book were written in his honour and have all been inspired by his work--in particular, his work in an area of moral philosophy known as 'population ethics', which is concerned with moral issues raised by causing people to exist. Until Parfit began writing about these issues in the 1970s, there was almost no discussion of them in the entire history of philosophy. But his monumental book Reasons and Persons (OUP, 1984) revealed that population ethics abounds in deep and intractable problems and paradoxes that not only challenge all the major moral theories but also threaten to undermine many important common-sense moral beliefs. It is no exaggeration to say that there is a broad range of practical moral issues that cannot be adequately understood until fundamental problems in population ethics are resolved. These issues include abortion, prenatal injury, preconception and prenatal screening for disability, genetic enhancement and eugenics generally, meat eating, climate change, reparations for historical injustice, the threat of human extinction, and even proportionality in war. Although the essays in this book address foundational problems in population ethics that were discovered and first discussed by Parfit, they are not, for the most part, commentaries on his work but instead build on that work in advancing our understanding of the problems themselves. The contributors include many of the most important and influential writers in this burgeoning area of philosophy.

Derek Parfit presents the third volume of On What Matters, his landmark work of moral philosophy. Parfit develops further his influential treatment of reasons, normativity, the meaning of moral discourse, and the status of morality. He engages with his critics, and shows the way to resolution of their differences. This volume is partly about what it is for things to matter, in the sense that we all have reasons to care about these things. Much of the book discusses three of the main kinds of meta-ethical theory: Normative Naturalism, Quasi-Realist Expressivism, and Non-Metaphysical Non-Naturalism, which Derek Parfit now calls Non-Realist Cognitivism. This third theory claims that, if we use the word 'reality' in an ontologically weighty sense, irreducibly normative truths have no mysterious or incredible ontological implications. If instead we use 'reality' in a wide sense, according to which all truths are truths about reality, this theory claims that some non-empirically discoverable truths-such as logical, mathematical, modal, and some normative truths-raise no difficult ontological questions. Parfit discusses these theories partly by commenting on the views of some of the contributors to Peter Singer's collection Does Anything Really Matter? Parfit on Objectivity. Though Peter Railton is a Naturalist, he has widened his view by accepting some further claims, and he has suggested that this wider version of Naturalism could be combined with Non-Realist Cognitivism. Parfit argues that Railton is right, since these theories no longer deeply disagree. Though Allan Gibbard is a Quasi-Realist Expressivist, he has suggested that the best version of his view could be combined with Non-Realist Cognitivism. Parfit argues that Gibbard is right, since Gibbard and he now accept the other's main meta-ethical claim. It is rare for three such different philosophical theories to be able to be widened in ways that resolve their deepest disagreements. This happy convergence supports the view that these meta-ethical theories are true. Parfit also discusses the views of several other philosophers, and some other meta-ethical and normative questions.

Are all of the commonly accepted aims of the use of law justifiable? Which kinds of behavior are justifiably prohibited, which kinds justifiably required? What uses of law are not defensible? How can the legitimacy or the ille gitimacy of various uses of law be explained or accounted for? These are questions the answering of which involves one in many issues of moral principle, for the answers require that one adopt positions - even if only implicitly - on further questions of what kinds of actions or policies are morally or ethically acceptable. The present work, aimed at questions of these kinds, is thus a study in the ethical evaluation of major uses of legal coercion. It is an attempt to provide a framework within which many questions about the proper uses of law may be fruitfully discussed. The framework, if successful, can be used by anyone asking questions about the defensibility of particular or general uses of law, whether from the perspective of someone considering whether to bring about some new legal provision, from the perspective of someone concerned to evaluate an eXisting provision, or from that of someone concerned more abstractly with questions about the appropriate substance of an ideal legal system. In addressing these and associated issues, I shall be exploring the extent to which an ethics based on respect for persons and their autonomy can handle satisfactorily the problems arising here.

Knowledge aims to fit the world, and action to change it. In this collection of essays, Onora O'Neill explores the relationship between these concepts and shows that principles are not enough for ethical thought or action: we also need to understand how practical judgement identifies ways of enacting them and of changing the way things are. Both ethical and technical judgement are supported, she contends, by bringing to bear multiple considerations, ranging from ethical principles to real-world constraints, and while we will never find practical algorithms - let alone ethical algorithms - that resolve moral and political issues, good practical judgement can bring abstract principles to bear in situations that call for action. Her essays thus challenge claims that all inquiry must use either the empirical methods of scientific inquiry or the interpretive methods of the humanities. They will appeal to a range of readers in moral and political philosophy.