by Theron Pummer (cross-posted on the Oxford Practical Ethics Blog)

How should we compare a decrease in average quality of life with a gain in population size?  Population ethics is a rigorous investigation of the value of populations, where the populations in question contain different (numbers of) individuals at different levels of quality of life.  This abstract and theoretical area of philosophy is relevant to a host of important practical decisions that affect future generations, including decisions about climate change policy, healthcare prioritization, energy consumption, and global catastrophic risks.

One of the central questions in population ethics is whether there is a satisfactory way of avoiding the Repugnant Conclusion, according to which:

For any possible population [called A] of at least ten billion people, all with a very high quality of life, there must be some much larger imaginable population [called Z] whose existence, if other things are equal, would be better even though its members have lives that are barely worth living (Parfit 1984).

Most people find the Repugnant Conclusion, i.e. the claim that Z is better than A, to be highly counterintuitive.  Thus many take the fact that Total Utilitarianism implies that Z is better than A to count against it, and attempt to find an alternative view in population ethics that avoids this implication.  However, as Derek Parfit (Reasons and Persons, 1984) and Gustaf Arrhenius (Population Ethics, forthcoming) have shown, it is difficult to avoid implying the Repugnant Conclusion without taking on board one or more other claims which are, in turn, highly counterintuitive.  Many of the puzzles in this area begin by setting up a smooth spectrum of populations, ranging from one in which everyone is at a very high quality of life (as in A) all the way to one in which everyone is at a very low but positive quality of life (as in Z), but where adjacent populations differ only slightly in terms of quality of life.

Here is the simplest such puzzle.  Start with population A.  Next consider B, whose members are at a quality of life 99.9% that of the people in A, but which is 100 times larger than A.  According to many, B is better than A.  The slight loss in quality is, according to them, more than compensated for by the enormous gain in quantity.  Next consider C, whose members are at a quality of life 99.9% that of the people in B, but which is 100 times larger than B.  For similar reasons, according to many, C is better than B.  And so on with D, E, F, etc. all the way down to Z.  Thus we have a series of premises:

  • B is better than A,
  • C is better than B, …and so on, all the way down to…
  • Z is better than Y.

If the relation “better than” is transitive, then these premises together imply that Z is better than A, i.e. they imply the Repugnant Conclusion.

Is there a plausible way to avoid this conclusion?  Some defenders of person-affecting views will get off the bus early, denying the very first premise that B is better than A.  According to them, what matters is “making people happy, not making happy people” – increasing population size does not as such count as an improvement.  There are powerful objections to such person-affecting views, as well as ingenious attempts to get them to imply the Repugnant Conclusion.  I won’t get into these issues here.  I will instead take it as plausible that more is better; that is, one way to make an outcome better, at least if other things are equal, is by bringing into existence more people with worth living lives.  Moreover, this is nontrivially better, such that just a slight decrease in quality is plausibly outweighed by a sufficiently large gain in quantity of lives lived.

There are three ways out of inconsistency:  we can claim (1) that one or more of the premises is not true, or (2) that transitivity of “better than” is not true, or (3) that the Repugnant Conclusion is true.  Solutions (1), (2), and (3) each seem implausible.  However, some people at Oxford working in population ethics have recently offered interesting ideas about how to minimize the implausibility of going with solution (1).  Derek Parfit appeals to the notion of imprecision in a paper in progress called “Can We Avoid the Repugnant Conclusion?” (given at the Oxford Moral Philosophy Seminar, podcast available here), and Teru Thomas appeals to indeterminacy in a paper in progress called “Vague Spectra” (given at the Oxford Population Ethics Project Work In Progress Seminar).  By appealing to these notions, we can, arguably, ease the pain of going with solution (1).  For now just consider indeterminacy (as it is more familiar than imprecision).

One might argue that indeterminacy arises in the puzzle case at hand, as within certain ranges it is indeterminate how quality trades off against quantity.  A plausible response is that the premises in question all involve tradeoffs outside the range of indeterminacy, and insofar as it’s plausible that B is better than A, C is better than B, and so on, it’s implausible that it’s indeterminate whether B is better than A, C is better than B, and so on.  However, is it less implausible to say this than to simply say (some of) the premises are false?  Even if so, it is unclear it’s less implausible to a sufficient degree to make (1) the overall least implausible solution to the puzzle.

Next suppose that indeterminacy comes in degrees (or, if you like, we could carry out the discussion in terms of degrees of truth).  Right now I’m not bald, but if you were to continually pluck hairs from my scalp, one by one, I would eventually be bald.  Imagine a spectrum of scalps, ranging from my actual scalp to a completely bald one, where adjacent scalps differ by only one hair.  We’d start out with 100% determinately not bald scalps and end up with 100% determinately bald scalps.  There are many scalps in the middle that are indeterminately bald.  But it seems plausible that they do not all enjoy the same degree of indeterminacy.  Presumably there are some pretty hairy scalps that are 99% determinately not bald.  It’s strictly indeterminate whether such a scalp is not bald, but it’s more determinate than whether a scalp with substantially fewer hairs is not bald (e.g. 60% determinately not bald).

If indeterminacy does come in degrees (or, again, if truth does), this opens up the door to offering solution (1) by claiming that there are at least some premises that are not 100% determinately true, but only (say) 99% determinately true.  It’s dubious there’d be much intuitive advantage gained here if epistemicism were true, as then it seems there’d be no real indeterminacy, but only uncertainty (according to this view there is precise point at which I’d go from not bald to bald, it’s just that we can’t know what this point is).  We could claim that not all of the premises are 100% certain, but then in offering solution (1) we would also be saying that there is a premise that is plain old false.

If there is real indeterminacy, and it comes in degrees, we could avoid the Repugnant Conclusion by claiming that there’s exactly one premise that’s only 99% determinately true.  This is because the transitivity of “better than” applies only to “better than” claims that are 100% determinately true.  However, one might offer a new transitivity principle to deal with degrees of indeterminacy; perhaps a plausible such principle would imply that if all but one of the premises were 100% determinately true – with the remaining one being 99% determinately true – then the Repugnant Conclusion is (at least) 99% determinately true.  I take it that this would not be much of an improvement, from the standpoint of someone interested in solution (1) as a way of avoiding the Repugnant Conclusion.  However, it does seem that if there were a large number of premises, and enough of them were only 99% determinately true, then there is no plausible transitivity principle that would imply the Repugnant Conclusion is determinately true to any significant degree.  (Similarly, it may be that “as bald as” is 99% determinately true when applied to adjacent pairs of scalps in the scalps spectrum, though 100% determinately false when applied to the first and last scalp).

I’ll end with some questions.  Does invoking indeterminacy (or some related notion) in this way help solve our puzzle?  Is saying that each premise is only 99% determinately true substantially less implausible than simply saying that there is a false premise?  Does this yield the least implausible solution to this particular spectrum puzzle about the Repugnant Conclusion?  And should we be optimistic that this kind of solution will help resolve other puzzles discussed in population ethics?