In the third edition of ‘Practical Ethics’ (2011), Peter Singer reexamines the so-called “replaceability argument,” according to which merely sentient beings, as opposed to persons (self-conscious and with a robust sense of time), are replaceable—it is in principle permissible to kill them provided that they live pleasant lives that they would not have had otherwise and that they be replaced by equally happy beings. On this view, existence is a benefit and death is not a harm. Singer’s challenge is to (...) avoid (i) the replaceability of persons while preserving the replaceability of merely sentient beings, (ii) the implication that parents are morally required to procreate if they can have happy children, and (iii) to do avoid these implications without having the proposed solution (the “debit view” of preferences) imply negative utilitarianism, or the conclusion that a nonsentient universe is better than any sentient universe. I review Singer’s changing views since 1975 and I argue that his attempt to avoid the replaceability of persons fails: either both non-persons and persons are replaceable or neither are. Singer can only avoid this conclusion by appealing to controversial metaethical claims (attitude-independent moral objectivism) and/or giving up on essential features of utilitarianism. (shrink)