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.

Jeff McMahan, University of Oxford,Tim Campbell, Institute for Futures Studies, Stockholm,James Goodrich, Rutgers University and University of Stockholm,Ketan Ramakrishnan, Yale Law School and the University of Oxford

Jeff McMahan is White's Professor of Moral Philosophy at the University of Oxford. He is the author of The Ethics of Killing: Problems at the Margins of Life (OUP, 2002) and Killing in War (OUP, 2009).

Tim Campbell is a researcher at the Institute for Future Studies at the University of Stockholm.

James Goodrich is a PhD student in philosophy at Rutgers and Stockholm University, working on moral and political philosophy.

Ketan Ramakrishnan is a JD candidate at Yale Law School and a DPhil candidate in philosophy at the University of Oxford.

Introduction, Jeff McMahan
I. CAUSING PEOPLE TO EXIST AND THE NON-IDENTITY PROBLEM
1. The Asymmetry, Ralf Bader
2. The Value and Probabilities of Existence, M. A. Roberts
3. Comparing Existence and Non-existence, Hilary Greaves and John Cusbert
4. The Impure Non-Identity Problem, Patrick Tomlin
5. Abortion and the Non-Identity Problem, Elizabeth Harman
6. A Partial Solution to the Non-Identity Problem: Regretting One was Born and Having a Life not Subjectively Worth Living, Andrew McGee and Julian Savulescu
II. THE REPUGNANT CONCLUSION, FUTURE GENERATIONS, AND EXTINCTION
7. Population Ethics Forty Years On: Some Lessons Learned from Box Ethics, Larry Temkin
8. Totalism without Repugnance, Jacob Nebel
9. Context-dependent Betterness and the Mere Addition Paradox, Johann Frick
10. Saving Posterity from a Worse Fate, Niko Kolodny
11. Against Large Number Scepticism, Andreas L. Mogensen
12. Are We Living at the Hinge of History?, William MacAskill
13. On Theory X and What Matters Most, S.J. Beard and Patrick Kaczmarek
III. EVALUATIVE IMPRECISION, INCOMMENSURABILITY, AND VAGUENESS IN VALUE
14. How to Avoid the Repugnant Conclusion, Ruth Chang
15. Can Parfit's Appeal to Incommensurabilities Block the Continuum Argument for the Repugnant Conclusion?, Wlodek Rabinowicz
16. Population Ethics and Conflict of Value Imprecision, Gustaf Arrhenius
17. Evaluative Imprecision, Scales of Value, and Vague Preference, Teruji Thomas
18. Sorites on What Matters, Theron Pummer
IV. PRIORITARIANISM IN POPULATION ETHICS
19. Prioritarianism, Population Ethics, and Competing Claims, Michael Otsuka
20. Quarantining Prioritarianism, Shlomi Segall