The Mere Addition Paradox
If adding happy people to the world is always an improvement, and reducing inequality is always an improvement, why does following both principles lead to a world you'd never choose?
Derek Parfit introduced this paradox in 1984 to show that our intuitions about population ethics are mutually inconsistent. Each step in the argument seems acceptable. The endpoint is a conclusion most people find monstrous. Parfit spent years trying to find a way out and concluded there may not be one.
Parfit, D. (1984). Reasons and Persons. Oxford University Press.
The sequence
Start with World A: a population of people living very good lives. Now consider World A+: all the same people, plus a new group living good but somewhat worse lives. The original group is unaffected.
Is A+ better than A? It seems like it should be. More welfare exists in A+. The original people are no worse off. The new people are glad to exist. Mere addition, adding people with lives worth living, appears to be an improvement.
Now compare A+ to World B: a population of the same total size as A+, but with inequality removed. Everyone lives at the same level, which is better than A+'s worse-off group but not as good as A+'s best-off group. B seems better than A+, because it has the same amount of welfare distributed more equally.
But B has more people living somewhat less well than World A. If B is better than A+, and A+ is better than A, then B is better than A. Repeat this process. Each iteration adds people and then equalizes. The endpoint is the Repugnant Conclusion: a vast population with lives barely worth living, which the argument forces us to call better than World A.
Why each step seems acceptable
The argument's power comes from the modesty of each move. Mere addition doesn't ask you to harm anyone. Redistribution toward equality has obvious appeal. Neither step requires accepting the Repugnant Conclusion directly.
The paradox is that three independently plausible claims, that mere addition is good, that equality is good, and that the Repugnant Conclusion is bad, cannot all be true simultaneously. At least one has to go. But none of them is obviously wrong.
Why there is no clean exit
Parfit explored every available escape route. Rejecting mere addition is hard: it seems to say that adding happy people makes things worse, or at least not better. Rejecting the move toward equality is hard: why should an unequal distribution be preferred to an equal one at the same total welfare? Accepting the Repugnant Conclusion is hard for obvious reasons.
The paradox is not a puzzle with a hidden answer. It is evidence that our intuitions about what makes outcomes better are genuinely inconsistent. A coherent population ethics may require abandoning something most people would not want to abandon.
Discussion questions
- Is a world of a trillion people with lives barely worth living better than a world of ten billion very happy people?
- Should we be trying to maximize the total amount of happiness in the world, or the average?
- Does the repugnant conclusion show a problem with the idea of maximizing overall happiness, or just with our intuitions?
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