TLDR: Take the population ethics quiz here: https://mdickens.me/pop-ethics/
Population ethics is an oft-overlooked subfield within ethics. Many people hold views that they don't realize contradict each other, or that have strange implications that they wouldn't endorse if they thought about it more.
Not just that—population ethics is a BIG DEAL. A lot of ethical decisions hinge on how you think about changes in future populations.
I'll give concrete examples below, but reading the examples might change your answers, so you should take the quiz first. It has 13 to 17 short questions. (Questions are skipped when they can't affect the results.)
Cross-posted from my website.
Nobody gets to ignore population ethics
There is no version of population ethics where you can just say, "Whatever feels intuitively right is what's right." Common-sense views on population ethics cannot all be true.
The quiz illustrates that fact. It asks you some questions about how you judge different situations involving varying populations. Then, based on your answers, it figures out:
- Do your views contradict each other?
- Do your views have counterintuitive implications that most people would dislike?
Answers are always contradictory or counterintuitive or both. The best-case scenario is that your views are consistent, and you bite the bullet on some unpopular conclusion.
If the quiz uncovers a conflict, it will tell you exactly which of your answers are mutually incompatible. Having a conflict is normal. But that's a good prompt to think about how you came to those answers, and how you might resolve the conflict. Did one of your answers come from an intuition that, upon further reflection, you might not agree with? Which intuitions are more reliable than others?
Concrete scenarios where population ethics matters
There are high-stakes real life situations that turn on how we answer population ethics dilemmas.
Example 1: Child mortality vs. family planning
This example comes from Greaves (2015).
Two of the most well-regarded global poverty interventions are malaria nets and family planning:
- The primary effect of malaria nets is that they prevent the deaths of young children.
- Family planning interventions reduce population growth—making existing family members better off, reducing Malthusian competition, etc.
The first-order effect of the former is that population goes up; the first-order effect of the latter is that population goes down. On its face, it seems strange to claim that these are both desirable. There are some ways to reconcile these views, but any attempted reconciliation produces new strange implications.
At minimum, we need to change how we estimate the cost-effectiveness of these two interventions. When people calculate the effectiveness of bednets and the like, they typically only consider the effect on life extension, not existing people; when calculating the effectiveness of family planning, they only consider the effect on existing people, ignoring the welfare of the people who would've been born otherwise. Considering both sides makes the interventions look less cost-effective.
I made a related argument in a 2016 post: GiveWell's Charity Recommendations Require Taking a Controversial Stance on Population Ethics. GiveWell recommendations assume that the value of a life saved derives precisely from the extra years of life lived, but also that there is nothing bad about causing someone not to be born (thus preventing them from experiencing 60–80 years of life). I showed that the apparent contradiction in this view is difficult to escape; the most straightforward resolution is that the Against Malaria Foundation is an order of magnitude less cost-effective than GiveWell's estimate suggests.
Example 2: Environmentalism
(I'm going to ignore wild animal welfare because that's a whole other issue. This example is just about how environmental destruction impacts future generations of humans.)
Most people intuitively feel that creating a new life is morally neutral. The standard account of this intuition is the person-affecting view: something can only be good if it's good for a person; a non-existent person isn't worse off for not being born, because there is no such person. However, this view creates some problems. An example: environmentalism.
Suppose a nation has two choices:
- It can burn through its natural resources, raising living standards for a century, but degrading the environment for future generations.
- It can conserve resources and protect the environment.
The choice has ripple effects into the future. These ripples change which children are conceived—a small change can cause a different sperm to win the race—so the two futures are populated by entirely different people. Therefore, no particular person is harmed by choosing to deplete resources.
This is Derek Parfit's "depletion vs. conservation" case from his analysis of the non-identity problem: if no definite person is harmed by environmental destruction, then person-affecting views have a difficult time explaining how any wrong is done.
These two examples illustrate that there are important real-world situations where we need to consider population ethics.
About the quiz
This project takes inspiration from Philosophy Experiments, which uses interactive philosophy quizzes to illustrate different viewpoints and tease out inconsistencies in your views. They didn't have a quiz for population ethics, so I made my own.
The quiz questions draw on Parfit's mere addition argument (Reasons and Persons, ch. 19) and his non-identity problem (ch. 16); Broome's argument that neutrality admits no range (Weighing Lives, ch. 10) and his collapsing principle against incomparability and greediness objection to neutrality (ch. 12); and Sen's properties α and β. The results describe positions staked out by Temkin and Rachels (denying transitivity); Tännsjö and Huemer (biting the bullet on the repugnant conclusion); Carlson (against the collapsing principle); among many other positions.
The quiz focuses on ranking outcomes, rather than ranking individuals' choices. Some views hold that the two are different. You might believe that, although world A is better than world B, it would nonetheless be wrong for a particular agent living in world B to bring about world A instead. I didn't address this distinction in the quiz because it would add great complexity.
I'm sure there are also some lesser-known views in population ethics that I overlooked when building the quiz. Similarly, the quiz may flag certain views as contradictory when I failed to see some subtle method to wriggle out of the contradiction.
AI usage disclosure
The initial draft of the quiz was generated wholesale by Claude Opus 4.8, then refined through many rounds of feedback. I vetted a list of population ethics views to ensure that the quiz handled them correctly. Finally, I manually reviewed the text in the final version and revised most of it. The revising process uncovered a few factual errors, but for the most part I only changed wording.
As always, this post itself was written by hand.
Source code
Source code is available on GitHub. Of particular interest is views-review.md, which lists two dozen different views on population ethics and how documents they would answer each quiz question.
Great tool, I liked it!
I played around with it a bit, and I think question 8 can be confusing. It says "Repeat the two moves from the last two questions:", but it actually does not do the moves the user preferred, but the move of picking the right-hand option over the left-hand option.
I imagine that for some audiences the welfare numbers/bar heights will feel arbitrary and made-up, and it is not really explained much. It does not have a unit associated to it, and phrases like "half as good" feel meaningless (compare how "half as warm" can mean a lot of different things).
To be clear, this is not my view and I do think it is possible to have linear scales for well-being (you can use probabilities to induce a linear scale once you can answer comparisons).