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How does utilitarianism deal with adding more people? (Question updated to include total utilitarianism)

Firstly, suppose we are using average utilitarianism. Suppose everyone in the world is super happy, we then "magically" generate a new person who is only slightly less happy and will not affect the happiness of anybody already existing. If we are just using an average, then we have then decreased it and so we should choose not to perform the action. It seems paradoxical that the morality of bringing this new person into the world depends on the happiness of everyone else. Can utilitarianism deal with this in a consistent manner?

Secondly, suppose we are using total utilitarianism. We then end up with the repugnant condition - that rather than having a small population very happy people, it would be better to have a much larger population of people living in terrible conditions (utility barely positive).

This is related to my question on why utilitarianism averages utility.

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  • possible duplicate of What responses are there to Singer's "Should this be the last generation?"
    – Joseph Weissman ♦
    Jun 16, 2011 at 12:25
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    @Joe, although I see the connection, I don't think this is a duplicate
    – Ben Hocking
    Jun 16, 2011 at 12:32
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    What makes you believe utilitarians average utility? Usually it's given as a (weighted) sum.
    – Xodarap
    Jun 16, 2011 at 16:08
  • @Xodarap: Updated question to take this into account
    – Casebash
    Jun 17, 2011 at 0:18
  • @Casebash: I've edited my answer to add a little more detail, but I fear a complete answer would essentially be a copy of the SEP article. I'm interested in what others say about the scope of your question though - maybe others think it is answerable.
    – Xodarap
    Jun 17, 2011 at 0:42

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Having read that other question, I think I understand the issue. I'll do my best without LaTeX, but this might not be pretty.

Suppose we consider everyone's utility to be of equal value. The total utility of a population would be the sum of each person's utility, i.e. utility_total = utility_1 + utility_2 + ...

By the definition of arithmetic mean, we can see that utility_total = mean * number_of_people. So an equivalent definition of utility_total deals with the arithmetic mean.

Here's where I think the confusion happens: utility_total does not deal only with the mean. It also includes the number of people.

So if adding this person would decrease the mean utility, that would be OK so long as net utility was increased. If their utility was positive, then it is guaranteed to increase net utility, so essentially the question "should we bring person X into the world" is just "will person X have positive utility?" Which (in your scenario) is independent of others' utilities, and so there is no problem.

EDIT: to be clear, this is what is sometimes known as "total utilitarianism". There does exist a variant of utilitarianism which does consider solely the average utility. In its naive form, your criticism is valid. I think proponents usually have some sort of "two-level" thinking whereby they switch between total and average utilitarianism as necessary.

To the best of my knowledge, "utilitarianism" usually means "total utilitarianism", which is why I answered this question this way. If you were interested in a defense of average utilitarianism, let me know.

EDIT 2: There are many possible solutions to the repugnant conclusion. So I'll give my favorite: there is no such thing as a life worth living.

I like it partly for shock value, but it also makes a good point: there is a fundamental difference between "this life is so good it requires you to be born" and "this life is so good it requires you to not die." I.e. once you've been born, moral laws apply to you which didn't apply before you were born.

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    Under utilitarianism, can a person have negative utility? Alternatively, given unlimited resources, would adding a person always increase utility_total? (Cases like adding another person to a life raft or to a poverty-stricken household obviously suffer from limited resources where a person's utility is negative due to circumstance.)
    – Jon 'links in bio' Ericson
    Jun 16, 2011 at 22:00
  • Briefly looking at your link, it seems that total utilitarianism has problems when dealing with variable populations as well
    – Casebash
    Jun 17, 2011 at 0:19
  • @Jon: a person can certainly have negative utility. This would indicate a life that's not worth living - some terminally ill patients desire euthanasia, for example. And it's also definitely possible to decrease total utility - the OP had the restriction that adding the new person wouldn't effect existing people, which is why I stated it like I did.
    – Xodarap
    Jun 17, 2011 at 0:25
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    "Once you've been born, moral laws apply to you which didn't apply before you were born." This sentence lacks meaning. Things that don't exist don't have properties such as being under moral obligation. More damaging, being under moral obligation may add to a person's utility rather than subtract from it. I assert that being human is better than being a dog because we are subject to higher moral laws. Being a dog is better than being a rock for the same reason. Comments don't allow for a defense of the idea. Perhaps, if the sentence is important to the answer, you could elaborate?
    – Jon 'links in bio' Ericson
    Jun 17, 2011 at 20:16
  • @Jon: I think we agree (if I understand you correctly). The "paradox" occurs because we treat the unborn as if they were already living. So the solution is to treat the unborn differently.
    – Xodarap
    Jun 17, 2011 at 20:31

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