In my regular discussions with people, as people run out of logical approaches to an argument, I frequently come across the argument:

...but if you were stuck on a desert island, would you...

The implication being that if you place the argument in a scenario that is extreme and unrealistic, and that argument fails in that scenario, the argument is invalid in the more frequent and realistic scenario.

My searches on Google seem to suggest this is called a Robinson Crusoe fallacy which seems apt but not formal.

Is Robinson Crusoe the correct term for this fallacy or is there a better one?

  • My usual response to this is "buy me an island and let's find out". :-p – tu-Reinstate Monica-dor duh Jan 26 '16 at 22:53
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    I'll try to write an answer in long form in a bit, but in short form, (a) there's no formal list of names for most informal fallacies. Thus, there's no correct term per se. Most broadly, this is a variation on "false premise" but that's not a very meaningful thing to say in philosophy. – virmaior Jan 26 '16 at 23:01
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    Depending on use, it might be a valid approach. If one is claiming something is universal, and someone provides a situation where your claim did not hold, then it suggests there's a need to caveat the domain where the claim is valid. I do know the opposite of this "fallacy" shows up a lot, in the form of "the claim works in the most common scenarios, so clearly we should not consider the possibility that it might not be universal." – Cort Ammon Jan 26 '16 at 23:40
  • Not on SO, people are arguing that this is not the Robinson Crusoe fallacy at all. – tu-Reinstate Monica-dor duh Jan 27 '16 at 2:50

I'm not sure if there's a named fallacy involved here. But it seems to me that the ring of Gyges might have some relevance or at least be interesting in this context.

The ring grants the wearer invisibility. This is the original "What would you do if you did not have to answer to society?" thought experiment. In the Republic, Glaucon uses the myth to show that no one with the ring would be immune to corruption, claiming that not even gods could resist it.

It might also be interesting to read Deleuze's short essay on desert (and deserted) islands. He gives a reading of Robinson Crusoe there, and is trying to show how the psychological movement towards the desert island is related to the geological movements that condition the island in the first place -- the continuous struggle between the land and the sea, the twin necessities of separation and creation (to really create, you had better be separate...)

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  • As I understand it, the ring of Gyges is based around the concept of a human flaw. If we consider the need to survive as a human flaw, then this would be correct. However, in the story s/he is given a power, whereas in this argument the person usually has all power eroded to the point where they have only one option - to betray a commitment. I have to think on this one further as it's not quite sitting right as far as I can understand it. – tu-Reinstate Monica-dor duh Jan 27 '16 at 2:48

There is simply no fallacy here, taking assertions to their logical extremes is a good test of whether or not there are premises missing from the remainder of the argument.

If your argument does not hold on a desert island, or on a plane (or in a box or with a fox...) then there is some reason the ordinary case is the ordinary case, and it may very well be important that you find it.

Omitted premises do make for false arguments, and they are a very common cause for two reasonable people not to see situations in the same light. There may be ideas in play that you have not recognized, which will sometimes provide a basis for a much more direct argument.

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  • I apologise if I've been misleading. The premise does actually hold on a desert island. The person arguing against it is implying that it wouldn't by taking it to extremes. – tu-Reinstate Monica-dor duh Jan 27 '16 at 4:25
  • Valid arguments depend only on the premises, not the 'accidents' of application. If the premises hold, it does not matter what the setting is. So there is no fallacy here by choosing a given setting. The extreme cases are still cases. Focussing on a minority case may be a rhetorical manipulation to waste time, but has no effect on the validity of the argument. – user9166 Jan 27 '16 at 15:49
  • @tudor If the premise does actually hold on a desert island, then why isn't your response to to the "what if...would you" simply "yes, the same"? If it is, then the "desert island" ploy is the "distraction fallacy" (changingminds.org/disciplines/argument/fallacies/…) of "many questions" (changingminds.org/disciplines/argument/fallacies/…). – Jeff Y Jan 27 '16 at 18:48
  • @JeffY Half the things on that page are not fallacies. They are manipulative rhetorical devices. Fallacies result in invalid arguments and the mental state of the arguer is not relevant to validity. If your argument breaks under any of the 'Many Questions', it just was not valid to begin with. – user9166 Jan 28 '16 at 18:23
  • @jobermark That's why they're called "informal fallacies". They allow invalid rebuttals to trump valid arguments in the "court of public opinion" when successful. – Jeff Y Jan 29 '16 at 12:28

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