Reasons, identity, and future people › Population size and the Repugnant Conclusion

Population ethics introduces another dimension: alternatives may contain different numbers of people. A total view adds the well-being of everyone in a population. For a fixed finite population with very high well-being, a sufficiently larger population with small positive well-being per person can have a greater total. This comparison assumes additively comparable well-being and holds other morally relevant features equal; it does not establish that the total view is correct.

Parfit calls the resulting implication the Repugnant Conclusion. His formulation in chapter 17 starts with any possible population of at least ten billion people, all enjoying a very high quality of life. It says that some much larger imaginable population would be better, other things equal, even though its members' lives would be barely worth living. The troubling feature is the trade between the quality and quantity of lives, rather than a claim that lives below the worth-living threshold become good merely by multiplying them.

Replacing totals with averages creates different difficulties. A rule that attends only to average well-being can oppose adding people with good lives when their lives fall below the existing average, even if the original population is unaffected. This does not conclusively establish the total view. It shows why rejecting one counterintuitive implication does not finish the search for a satisfactory theory.

The Mere Addition discussion examines pressures created by comparisons among populations. Apparently acceptable steps can lead toward conclusions we find hard to accept. Each comparison needs its own justification. A diagram or a sequence of agreeable-sounding descriptions would not remove the need to examine the assumptions connecting the steps.

Parfit's search for a satisfactory Theory X is unfinished in this book. He does not present reductionism as a settled solution to the Repugnant Conclusion. The distinction matters because the book teaches us to recognize competing requirements whose reconciliation remains difficult. Understanding the problem is an achievement even when the desired comprehensive principle has not been supplied.