The ideal observer theory (https://en.wikipedia.org/wiki/Ideal_observer_theory) says "A is better than B if an impartial and fully informed observer would choose A over B... here, A and B are moral actions/situations/events/consequences, etc.

Okay, so let's say that I walk down the street and kill the first person I run into. I then turn around and ask the nearest "impartial and fully informed observer" whether that was wrong or not.

How can that person possibly answer "Yes, that was wrong" to that question?

The only argument I've heard is that the observer could say "Yes, it must be wrong, because if this was right, it could affect me one day if I got killed, and that I would not prefer" ... however this argument breaks the premise of impartiality. The observer is IMPARTIAL to the event taking place, which means the observer is NOT a human being who would get killed as easily as the person I just killed. Therefore, the observer should NOT care (in principle) if any or all humans died, due to their impartiality.

So what is the argument that this observer can possibly make? Is there even one? If not, isn't the theory plain useless?

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    You are missing the point. In moral theory a moral rule would NEED TO APPLY UNIVERSALLY EVERYWHERE ON EARTH. That means you are now setting the rule for any human being regardless of who the person is has they right to be killed. You just killed someone & there is no problem correct? That means YOU TOO are also on the menu just like any other human being including all the people you happen to love, the President of your country, you King, your Priest, any one in authority, the top ranked police officer, etc. Any one and everyone is on the chopping block at ANY TIME with NO EXCEPTIONS period.
    – Logikal
    Feb 11, 2021 at 18:45
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    Firstly, this argument implies that one is not impartial as soon as one is human, while impartiality means not being involved here. Secondly, you quote something about choosing one act over the other. I do not see that reflected in your scenario. Thirdly, the impartial and fully informed person does not have to justify the judgement. It is assumed it will be correct. Full stop
    – Philip Klöcking
    Feb 11, 2021 at 22:15
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    @PhilipKlöcking - Reading the description of this ethical theory, I get the impression that the idea is to use the ideal observer as a thought-experiment, and try to make an argument for what they would conclude in a particular situation in order to argue that this is the ethically correct action. If you just say "they are ideal so whatever they conclude must be correct by assumption" isn't helpful in drawing any conclusions about specific situations, since we don't have such an individual on hand.
    – Hypnosifl
    Feb 11, 2021 at 22:21
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    @Logikal - "In moral theory a moral rule would NEED TO APPLY UNIVERSALLY EVERYWHERE ON EARTH" This is much too broad of a generalization, there are plenty of moral theories where this wouldn't be the case (any form of consequentialism for example). Even when it comes to deontological moral theories like Kant's categorical imperative, many would still allow rules of the form "for any person with quality X, you should take action Y towards them", not that if you take action Y towards one person you have to take the same action towards every person on earth regardless of circumstance.
    – Hypnosifl
    Feb 11, 2021 at 22:24
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    Firth's idea was that we have some internal wellspring of immaculate morality that gets polluted by ignorance, lack of imagination, biases, etc. Ideal observers are defined to be free of those pollutants, but "otherwise normal humans". They supply oracular moral judgements, not explain them by giving arguments. Judgments are starting points of arguments, not conclusions from premises. And impartial all-knowing "normal human" would judge murder for no reason wrong, which you can verify by consulting your (cleansed) personal moral wellspring. But there is no point asking why on this theory.
    – Conifold
    Feb 12, 2021 at 1:31

2 Answers 2


The resolution to this apparent paradox might be hidden somewhere in the intended meaning of the phrase fully informed. Presumably, one cannot be fully informed without also being able to fully comprehend the significance of what is at stake in your example: the lived experience of a human being, and also the suffering through which that lived experience is abbreviated. A rock could be just as impartial as the most perfect judge, but the perfect judge is (perhaps uniquely) capable of experiencing and appreciating the full effect and context of their own existence, and of aligning their actions with their intent. The latter is also what makes the judge an ethical agent.

  • One also supposes that the Wikipedia entry in question might do with some editing... Or that it's not being quoted aright in the OP. Mar 14, 2021 at 0:10

After having read the Wikipedia article I'd agree that this theory makes some assumptions on what morality is.

Like if you had full knowledge of the fact of what is happening you could make an informed judgement and wouldn't require any heuristics, but this makes the assumption that there is ONLY ONE way how to judge that. Which is further underlined by the fact that there is no distinction made between who the ideal observer is. Like it's not about the observer it's just about what they have access to.

Meaning the meaning of "neutrality" is kinda dubious. Like sure if there is a conflict of interest then that would mean that you don't pick a side. But you could pick a side in terms of literally siding with a person AND in terms of having a bias towards an outcome. And while it seems to reject the first one, it almost necessitates the second. Because without that you wouldn't be able to judge at all.

So there seems to be an explicit assumptions that at least something like "the human condition" or whatnot would shape exactly one framework of morality if we just had full information.

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