Abstract: People are often faced with decisions that involve weighing the lives of some people against the lives of others, or weighing lives against other goods. This book aims to develop a moral theory that can help with making these practical decisions. It is a theory of value, which includes an account of how good it is to extend a person’s life, and also an account of how good it is to have new lives in the world — of the value of adding a new person to the world’s population. It is a theory about the aggregation of people’s wellbeing: of how the wellbeing that comes to a person at different times in her life comes together to determine the overall value of her life, and of how different people’s wellbeing comes together to determine the overall value of the world. The book pays particular attention to the common intuition that adding people to the population is ethically neutral, but eventually rejects it. The book’s conclusion is a version of utilitarianism. The method is formal, but the presentation is as informal as possible.

Keywords: life, population, wellbeing, utilitarianism, moral theory, theory of value, extending life, saving lives, neutrality intuition, population ethics