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In Derek Parfit's original formulation the Repugnant Conclusion is characterized as follows: “For any possible population of at least ten billion people, all with a very high quality of life, there must be some much larger imaginable population whose existence, if other things are equal, would be better even though its members have lives that are barely worth living” (Parfit 1984). The Repugnant Conclusion highlights a problem in an area of ethics which has become known as population ethics . The last three decades have witnessed an increasing philosophical interest in questions such as “Is it possible to make the world a better place by creating additional happy creatures?” and “Is there a moral obligation to have children?” The main problem has been to find an adequate theory about the moral value of states of affairs where the number of people, the quality of their lives, and their identities may vary. Since, arguably, any reasonable moral theory has to take these aspects of possible states of affairs into account when determining the normative status of actions, the study of population ethics is of general import for moral theory. As the name indicates, Parfit finds the Repugnant Conclusion unacceptable and many philosophers agree. However, it has been surprisingly difficult to find a theory that avoids the Repugnant Conclusion without implying other equally counterintuitive conclusions. Thus, the question as to how the Repugnant Conclusion should be dealt with and, more generally, what it shows about the nature of ethics has turned the conclusion into one of the cardinal challenges of modern ethics.

In Derek Parfit's original formulation the Repugnant Conclusion is characterized as follows: “For any possible population of at least ten billion people, all with a very high quality of life, there must be some much larger imaginable population whose existence, if other things are equal, would be better even though its members have lives that are barely worth living” (Parfit 1984). The Repugnant Conclusion highlights a problem in an area of ethics which has become known as population ethics . The last three decades have witnessed an increasing philosophical interest in questions such as “Is it possible to make the world a better place by creating additional happy creatures?” and “Is there a moral obligation to have children?” The main problem has been to find an adequate theory about the moral value of states of affairs where the number of people, the quality of their lives, and their identities may vary. Since, arguably, any reasonable moral theory has to take these aspects of possible states of affairs into account when determining the normative status of actions, the study of population ethics is of general import for moral theory. As the name indicates, Parfit finds the Repugnant Conclusion unacceptable and many philosophers agree. However, it has been surprisingly difficult to find a theory that avoids the Repugnant Conclusion without implying other equally counterintuitive conclusions. Thus, the question as to how the Repugnant Conclusion should be dealt with and, more generally, what it shows about the nature of ethics has turned the conclusion into one of the cardinal challenges of modern ethics.

The Repugnant Conclusion is closer to infinity-based arguments, such as Pascal’s Wager, than it at first appears. Both rely on an unbounded set of payoff comparisons. It is possible to restructure Pascal’s Wager to resemble the Repugnant Conclusion more closely, as the use of infinity is not central to the former. I then consider settings in which the set of comparisons is bounded, so as to differentiate Parfit’s problem from the more general issues involved with very large numbers. We then find the Repugnant Conclusion no longer necessarily arises as a matter of logic rather is an empirical contingency. I then present some plausible intuitions under which the Repugnant Conclusion never arises. The paradoxical nature of Parfit’s Repugnant Conclusion is traced to the simultaneous application of two inconsistent outside observer constructs: one to judge the Repugnant Conclusion as repugnant, and another to define the utility scale for a marginally worthwhile life. Once the two constructs are made consistent, the Repugnant Conclusion can be defused.

A set of arguments shows that either the Repugnant Conclusion and its variants are true or the better-than relation isn’t transitive. Which is it? This is the most important question in population ethics. The answer will point the way to Parfit’s elusive Theory X.

A set of arguments shows that either the Repugnant Conclusion and its variants are true or the better-than relation isn't transitive. Which is it? This is the most important question in population ethics. The answer will point the way to Parfit's elusive Theory X.

Population axiology concerns how to evaluate populations in regard to their goodness, that is, how to order populations by the relations “is better than” and “is as good as”. This field has been riddled with “paradoxes” which seem to show that our considered beliefs are inconsistent in cases where the number of people and their welfare varies. Already in Derek Parfit’s seminal contribution to the topic, an informal paradox — the Mere Addition Paradox — was presented and later contributions have proved similar results.1 All of these contributions, however, have one thing in common: They all involve an adequacy condition that rules out Parfit’s Repugnant Conclusion: The Repugnant Conclusion: For any perfectly equal population with very high positive welfare, there is a population with very low positive welfare which is better, other things being equal.2 A number of theorists, however, have argued that we should accept the Repugnant Conclusion and hence that avoidance of this conclusion is not a convincing adequacy condition for a population axiology. Torbjörn Tännsjö, for example, argues that the Repugnant Conclusion is not at all repugnant but rather “an unsought, but acceptable, consequence of hedonistic utilitarianism”:3..

On the Total Principle, the best state of affairs (ceteris paribus) is the one with the greatest net sum of welfare value. Parfit rejects this principle, because he believes that it implies the Repugnant Conclusion, the conclusion that for any large population of people, all with lives well worth living, there will be some much larger population whose existence would be better, even though its members all have lives that are only barely worth living. Recently, however, a number of philosophers have suggested that the Total Principle does not imply the Repugnant Conclusion provided that a certain axiological view (namely, the ‘Discontinuity View’) is correct. Nevertheless, as I point out, there are three different versions of the Repugnant Conclusion, and it appears that the Total Principle will imply two of the three even if the Discontinuity View is correct. I then go on to argue that one of the two remaining versions turns out not to be repugnant after all. Second, I argue that the last remaining version is not, as it turns out, implied by the Total Principle. Thus, my arguments show that the Total Principle has no repugnant implications.

I defend the 'Repugnant' Conclusion that for any possible population of happy people, a population containing a sufficient number of people with lives barely worth living would be better. Four lines of argument converge on this conclusion, and the conclusion has a simple, natural theoretical explanation. The opposition to the Repugnant Conclusion rests on a bare appeal to intuition. This intuition is open to charges of being influenced by multiple distorting factors. Several theories of population ethics have been devised to avoid the Repugnant Conclusion, but each generates even more counterintuitive consequences. The intuition opposing the Repugnant Conclusion is thus among the best candidates for an intuition that should be revised.