Repugnant Conclusion

Overview

The Repugnant Conclusion is a central problem in population ethics, first systematically developed by Derek Parfit in Reasons and Persons (1984). It highlights a tension between seemingly plausible moral principles about the value of lives and populations, and an apparently counterintuitive implication about what would make the world better overall.

Intuitively, many people judge that a world in which a relatively small number of people live very high-quality lives is better than a world containing an enormous number of people whose lives are barely worth living. Yet certain influential moral theories—especially total utilitarianism and related aggregative views—appear to imply the opposite. Parfit labeled this implication the “Repugnant Conclusion” to capture its conflict with common moral intuitions.

Parfit’s Formulation

Parfit’s argument begins with a comparison between different possible populations, each characterized by:

• Number of people, and
• Level of welfare (or well-being) per person.

Consider:

• Population A: a relatively small population whose members all enjoy very high welfare.
• Population Z: a very large population whose members all have lives that are just barely worth living (their positive experiences just slightly outweigh their negative ones).

Under total utilitarianism, the moral value of a population is the sum of individual welfare levels. On this view, a population can be better than another even if everyone in it is worse off, provided that there are enough additional lives with positive welfare to raise the total.

Parfit’s reasoning involves a sequence of intermediate populations:

1. Start with A: few people, very high welfare.
2. Construct B: a larger population where people are slightly worse off but still well above a life barely worth living. Many find it plausible that B can be at least as good as A if the total well-being is greater and no one is badly off.
3. Continue this process in small steps (adding people, slightly lowering average welfare) through a series of populations, each apparently “not worse than” the last by the same kind of reasoning.
4. Eventually, this leads to Z: a population so large that, although each life is only barely worth living, the total sum of welfare vastly exceeds that of A.

Given these steps plus a commitment to the transitivity of “better than” or “at least as good as,” the theory implies:

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Repugnant Conclusion: For any possible population of at least ten billion people, all with a very high quality of life, there must be some much larger possible population whose existence, if other things are equal, would be better even though its members have lives that are barely worth living.

Parfit did not claim that this conclusion is logically incoherent; rather, he argued that it clashes strongly with many people’s moral intuitions.

Responses and Theoretical Options

Philosophers have reacted to the Repugnant Conclusion in several main ways, each with its own costs.

1. Accepting the Repugnant Conclusion

Some theorists accept the conclusion as a counterintuitive but true implication of aggregative ethics. They argue that:

• Moral intuitions may be unreliable when assessing extremely large or abstract populations.
• The appeal of simple, systematic theories like total utilitarianism may outweigh the discomfort of the conclusion.
• “Repugnance” alone is not decisive evidence of falsehood; history shows that moral progress often involves revising intuitive judgments.

On this view, the Repugnant Conclusion is indeed surprising, but not a reductio of total utilitarianism.

2. Rejecting Total Utilitarianism

Others treat the Repugnant Conclusion as a reductio ad absurdum of simple totalism and seek alternative population principles. Several strategies have emerged:

• Average utilitarianism: Evaluate populations by their average welfare, not total. This avoids preferring vast low-quality worlds, but has its own counterintuitive implications, such as:

  • It can deem it bad to add a person with a good life if doing so slightly lowers the average.
  • It can rank a world where many people are miserable but a few are ecstatic as better than one with uniformly good lives.

• Critical-level utilitarianism: Add a fixed critical level of welfare; only welfare above this level contributes to the moral value of a life. This can reduce the force of the Repugnant Conclusion, but:

  • Requires an arbitrary-seeming choice of critical level.
  • Still faces versions of the same problem at the margin.

• Person-affecting views: Claim that an outcome is better only if it is better for someone (or no one is made worse off). Adding extra people is then not straightforwardly better, since it does not benefit existing individuals. Such views often avoid the Repugnant Conclusion, but they encounter other problems:

  • They may struggle to explain why creating happy lives is good at all.
  • They face puzzles like the Non-Identity Problem, where identity depends on which choices are made.

• Non-aggregative or pluralist views: Some propose that overall goodness does not reduce to a single numerical function. They emphasize:

  • Limits to aggregation (e.g., the quality of lives sets constraints).
  • Value pluralism (e.g., justice, equality, and rights matter independently of total welfare). These approaches, however, often become complex and may sacrifice the formal elegance of utilitarian models.

3. Modifying Structural Assumptions

Another avenue questions structural assumptions used in Parfit’s setup, such as:

• Transitivity of “better than”
• The assumption that any small worsening in average welfare can be morally outweighed by enough additional lives
• The idea that there must always be a precise overall ranking of all possible populations

Revisions here can block the derivation of the Repugnant Conclusion, but at the expense of familiar principles in ethical and rational choice theory.

Significance in Population Ethics

The Repugnant Conclusion has reshaped population ethics by showing that no simple theory seems able to respect all of our intuitions about:

• The value of quality of life vs. sheer quantity of lives
• The moral importance of creating new happy individuals
• Fairness and distribution of welfare across persons and generations

Further developments, such as Gustaf Arrhenius’s impossibility theorems, suggest that any theory satisfying a set of initially attractive axioms will yield some conclusion as counterintuitive as the Repugnant Conclusion (or worse). This has led many philosophers to think that:

• Some deeply held intuitions must be revised, or
• We must accept that no fully satisfactory, simple population axiology is available.

The Repugnant Conclusion thus serves as a focal point for debates about utilitarianism, future generations, climate policy, and existential risk, where choices affect not only how well people live but how many people will ever exist. It remains an open question which theoretical sacrifices are most acceptable in responding to it, and different ethical frameworks continue to offer competing resolutions without clear consensus.