I would like to acknowledge a significant intellectual debt to Joe Bankman and our sons, Sam and Gabe. When Sam was about fourteen, he emerged from his bedroom one evening and said to me, seemingly out of the blue, “What kind of person dismisses an argument they disagree with by labelling it ‘the Repugnant Conclusion’?” Clearly, things were not as I, in my impoverished imagination, had assumed them to be in our household. Restless minds were at work making sense of the world around them without any help from me. In the years since, both Sam and Gabe have become take-no-prisoners utilitarians, joining their father in that hardy band. I am not (yet?) a card-carrying member myself, but in countless discussions around the kitchen table, literally and figuratively, about the subject of this book, they have taught me at least as much as I have taught them. More importantly, they have shown me by example the nobility of the ethical principle at the heart of utilitarianism: a commitment to the wellbeing of all people, and to counting each person—alive now or in the future, halfway around the world or next door, known or unknown to us—as one.

Among the things which we can to some extent influence by our actions is the number of minds which shall exist, or, to be more cautious, which shall be embodied at a given time. It would be possible to increase the total amount of happiness in a community by increasing the numbers of that community even though one thereby reduced the total happiness of each member of it. If Utilitarianism be true it would be one’s duty to try to increase the numbers of a community, even though one reduced the average total happiness of the members, so long as the total happiness in the community would be in the least increased. It seems perfectly plain to me that this kind of action, so far from being a duty, would quite certainly be wrong.