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.
Ah, this is great! Thanks so much for doing it. I want to honour this the only way philosophers know how, which is to quibble with some details in an effort to improve it. (I thought a lot about population ethics during my PhD, but I haven't published anything evaluating the theories).
On your comment that the answers are contradictory or counterintutive or both, I want to add this is very much agreed on in the field. The famous result is Arrhenius (2000), which showed there are a number of assumptions we might want to make about population ethics, but they are mutually inconsistent - you can't eat your cake and still have it.
Because population ethics is so vexing, it's very tempting to consider it in light of theories of moral uncertainty. So, rather than thinking you are, or have to be, 100% certain in one view, you recognise that you have credence in multiple views, and then you'd appeal to a theory of moral uncertainty (there are a few options here, which complicates things) to determine what's appropriate to do in light of your uncertainty. Implicitly, this quiz - along with standard philosophical discourse - assumes a 'My Favourite Theory' approach to moral uncertainty (act if you're certain in theory you think is mostly likely correct). Accounting for (other positions in) moral uncertainty may slightly break the quiz, as there can be more than one justification for picking an answer. Admittedly, this would make the quiz much more fiddly and be harder to implement.
One example is Q4, where you give two identical populations, except there's a new, miserable person in the second. I'm sympathetic to a person-affecting view (count only sure-to-exist lives) and if I were 100% confident in that I'd say they were exactly as good each other. However, when I account for moral uncertainty, as I give some weight to possible lives, the second population is worse as that miserable life breaks the tie. So, I gave the 'wrong' answer if I ignore moral uncertainty, but I gave what I think is the right answer after accounting for it. I'm not sure how your quiz interprets this, but it told me I had a lexical or critical view, which I wouldn't agree with. Same issue for Q5 and Q10, which are about identical populations except for 1 additional life.
You phrase Q7 and Q8, which are related to the Repugnant Conclusion, as if they are structurally identically. But they are not. Q7 is a same people case, and asks if it's better to have higher average welfare. Q8 is about going from the A population to the Z population (the classic Repugnant Conclusion challenge), but each step in Q8 you're adding new people, whereas in Q7 you had the same people. So, wearing my person-affecting hat, I interpret Q7 and Q8 quite differently: I'm happy to have a higher total welfare for the same population (Q7), but I'm inclined not to go to step B in Q8, as that means creating new people (no value) and reducing the welfare of the existing people (negative value). You frame Q8 as "do it again" but I'd argue we're doing something relevantly different between Q7 and Q8.
Q12 and Q13 are about transitivity. In Q12 you're looking at 3 worlds where the first is better than the second, and second is better than the third. For Q13 you replace 'better than' with 'exactly as good as'. You give two options in each case ("yes, always", "no, not always") but I wanted there to be a third option "it depends on the details". Specifically, I'm wondering about whether we've got the same or different people across the three worlds.
Finally, I agree that accounting for population ethics, and population effects, can substantially influence the priorities in unexpected and arguably repugnant way. You pointed out life-saving and life-averting invertions are in tension. An extension of this is the more(/less) you think the Earth is overpopulated, the less(/more) valuable it is to save lives. Another is that if you think factory farming is bad because of the negative welfare it causes, that should reduce the value of saving lives to some (unknown and perhaps unknowable) extent. Many years ago, I wrote about these in my PhD thesis and subsequently published a paper on the meat eater problem. I confess I find this all weird to think about, which is part of the reason I've shifted onto other things since...
Thanks again for creating it!
Thanks for the comments! I feel honored :P
Miscellaneous responses:
I was originally going to cite Arrhenius because I was under the mistaken impression that he wrote in the 1950s or 60s and Parfit drew inspiration from him. But while making the quiz I realized it was the other way around. As I understand, Arrhenius' impossibility proof is qualitatively the same thing as what Parfit laid out in Reasons and Persons, the difference being that Parfit only gave an informal proof and Arrhenius made it mathematically rigorous. I haven't read either original source but that's my understanding.
The quiz doesn't allow for moral uncertainty. The honest reason why not is that I didn't think to do that, but thinking about it now, it sounds really hard because it creates a combinatorial explosion of outcomes. On Q4 for example, you could also answer "uncertain between K is better and they are equal" or "uncertain between K is better and they are incomparable" or "uncertain between all three", or if you want to get even more specific, "pretty sure K is better but maybe they're incomparable", ...
I wanted to make the quiz as comprehensive as possible while still being reasonably short. In particular I didn't want to claim an answer was contradictory when actually it wasn't, and I spent a lot of time looking for ways philosophers have proposed resolutions to seemingly-contradictory sets of answers. (Including hours spent faithfully representing views that so far ~zero quiz-takers have endorsed.) One thing I explicitly didn't cover is the difference between preferred acts vs. preferred outcomes, because it would add an amount of complexity disproportionate to its usefulness. Moral uncertainty is another issue like that, I think.
Q6 (comparing A and A+) does add new people. The move from A to B is first asked in terms of moving from A to A+ (Q6) and then A+ to B (Q7), and then you can chain those two moves down to Z, which is what Q8 is asking about. As I understand it, this is identical to Parfit's construction of the mere addition paradox. The step where you add new people is in Q6, not in Q7, so the "do it again" is a reference to doing the Q6 step again. (And also doing the Q7 step again, but sounds like you are taking issue with the adding-new-people part.)
Possible that I'm still missing something here, please tell me if I am.
If it depends on the details, then wouldn't the answer be "no, not always"?