Finally in situation B there is a single population whose size is the sum of the two populations in situation B- and at the same level of happiness. Going from A to B

The difference between the situations A and A+ is only in the existence of extra people at a lower level of happiness. If the two populations were known to each other and were aware of the inequality this would arguably constitute social injustice. However as they do not Parfit says this represents a Mere Addition and it seems implausible to him that it would be worse for the extra people to exist. Thus he argues A+ is not worse than A.

Furthermore there are the same numbers of people on both sides of the divide in situation B- as there are in situation A+. The average happiness in B- is higher than A+ (though lower than A). Since A+ and B- have the same number of people and because there is a greater level of equality and average happiness in B- it seems that all things considered B- is better than A+. But the situations B- and B are the same except the communication gap is removed. It seems that B is at least as good as B-. The Repugnant Conclusion

We can then repeat the argument and imagine another divide and ask if it would be better for more extra people to exist unknown to the people in B and so on as before. We then arrive at a situation C in which the population is even larger and less happy though still with lives worth living. And if we agree that B is not worse than A then we would conclude in the same fashion that C is not worse than B. But then we could repeat that argument again finally arriving at a situation Z in which there are an enormous number of people whose lives are worth living but just barely. Parfit calls this the Repugnant Conclusion and says that Z is in fact worse than A and that it goes against what he believes about overpopulation to say otherwise. This is a contradiction but it is not clear how to avoid it. Objections to and resolutions of the paradox The paradox is immediately resolved by the conclusion that the "better than" relation is not transitive meaning that our assertion that B- is better than A by way of A+ is not justifiedit could very well be the case that B- is better than A+ and A+ is better than A and yet A is better than B-. This is of course incompatible with any form of utilitarianism. Temkin argues for this approach. The paradox can be defeated by asserting that A+ is actually worse than A in other words that adding people of less-than-average happiness into the world makes the overall situation worse. This is the conclusion of "average utilitarianism" which aims at maximizing average happiness. However this solution may commit one to the position that it is actually bad for people of less than average happiness to be born even if their lives are worth living. Another position might argue for some threshold above the level at which lives become worth living but below which additional lives would nonetheless make the situation worse.citation needed Parfit argues that for this position to be plausible such a threshold would be so low as to apply only to lives that are "gravely deficient" and which "though worth living ... must be crimped and mean." Parfit calls this hypothetical threshold the "bad level" and argues that its existence would not resolve the paradox because population A would still be better than an enormous population with all members having lives at the "bad level." This section's factual accuracy is disputed. Please help to ensure that disputed facts are reliably sourced. See the relevant discussion on the talk page. (August 2008) Parfit also considers an objection where the comparison between A+ and B- is attacked. The comparison between A and A+ was partly dependent on their separation. Thus A+ and B- might simply be incomparable. Parfit gives the Rich and Poor example in which two people live in separate societies and are unknown to each other but are both known to you and you have to make a choice between helping one or the other. Thus despite their separation it is meaningful to ask whether A+ is better than B- or not. One could deny that B- is better than A+ and therefore neither is B. But this rejection implies that what is most important is the happiness of the happiest people and commits one to the view that a smaller decrease in the happiness of the happiest people outweighs a bigger increase in the happiness of less happy people at least in some cases. Parfit calls this the Elitist view. Of course one can simply accept the Repugnant Conclusion. Torbjrn Tnnsj argues that we have a false intuition of the moral weight of billions upon billions of lives "barely worth living". He argues that we must consider that life in Z would not be terrible and that in our actual world most lives are actually not far above and often fall below the level of "not worth living". Therefore the Repugnant Conclusion really isn't so repugnant. See also Average and total utilitarianism Carrying capacity and ecological footprint A Theory of Justice by John Rawls Minimax Overpopulation Utility monster Sorites Paradox External links The Repugnant Conclusion (Stanford Encyclopedia of Philosophy) Alex Tabarrok's The Philosophical Cow (an application to the animal rights issue) References Parfit Derek. Reasons and Persons ch. 17 and 19. Oxford University Press 1986. Temkin Larry. Intransitivity and the Mere Addition Paradox Philosophy and Public Affairs Vol. 16 No. 2 (Spring 1987) pp. 138187 Tnnsj Torbjrn. Hedonistic Utilitarianism. Edinburgh University Press 1988. Contestabile Bruno. On the Buddhist Truths and the Paradoxes in Population Ethics Contemporary Buddhism Vol. 11 Issue 1 pp. 103113 Routledge 2010