Mere addition paradox
The Mere Addition Paradox is a problem in utilitarian ethics, due to Derek Parfit, and first appearing in his book, Reasons and Persons.
The paradox
The paradox appears to show that it is better to have a large population, where everyone has a life that is just barely worth living, than a small population where everyone is very happy.
The paradox arises from consideration of 3 different possibilities. The following diagrams show different populations, with population size on the x-axis, and the happiness of each individual on the y-axis.
| File:Mere Addition A.png | File:Mere Addition A Plus.png | File:Mere Addition B.png |
| A | A Plus | B |
|---|---|---|
In population A, everyone is very happy.
Population A Plus consists of 2 groups - the same group as in A has had added to it a group that is moderately happy. As this is a mere addition of reasonably happy people, Parfit argues that it is no worse than the state of affairs in A.
Population B is the same size as population A Plus, but the average happiness is higher than A Plus, though slightly lower than in A. Since the average happiness is higher than in A Plus, Parfit argues that the state of affairs in B is no worse than that of A Plus, and therefore, no worse than that of A.
The paradox comes because this argument is repeatable until we reach something like Z, a huge population of people whose lives are only just worth living (on these graphs, negative values would indicate lives not worth living).
| File:Mere Addition Z.png |
| Z |
|---|
Thus, the state of affairs in Z is no worse than the state of affairs in A. Parfit calls this the Repugnant Conclusion, and rejects it, but says he does not have a solution.
Objections
Some say that this paradox can be defeated by simply denying its first axiom: that adding people of less-than-average happiness in the world doesn't make the overall situation worse. This is by no means universally accepted, and there is a branch of utilitarianism that aims at maximising the average happiness. However, this position does involve the claim that it is actually bad for happy people to be born, if they are less happy than the average.
Alternatively, one could deny that the redistribution of happiness in the move from A Plus to B makes things better. However, this would seem to involve the claim that what is most important is the happiness of the happiest people, and a small increase in that is worth a (bigger) decrease in the happiness of less happy people.