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I'm hoping to find a name already in somewhat common usage for a fallacy of the following form:

  1. A person claimed X.
  2. Therefore either X is true or the person is lying.

I've seen this fallacy incorporated into a larger argument in the following way:

  1. A person claimed X.
  2. It follows from #1 that either X is true or the person is lying.
  3. It is unlikely/impossible that the person is lying.
  4. Therefore X is true.

In fact, at least one other possibility typically exists -- the person may be mistaken. It is basically a special case of a false dichotomy, but I'm hoping for a term that more specifically fits this particular type of false dichotomy.

  • There is no special name, and in many cases such inferences are plausibly valid because alternatives are highly implausible in many contexts where the inference is made. Those would be truncated arguments (with unstated premises) rather than fallacies. For instance, "you are lying" is a valid response to "I didn't do it" if there is nobody else around who could, and amnesia is even more implausible. – Conifold May 17 '17 at 21:25
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There are two possibilities that we can consider here. The first, as you brought up, is the False Dichotomy Fallacy. Our person assumes there is only two possibilities, A and B, so after eliminating A she believes she has proven B.

The second fallacy is referred to as the Blind Loyalty Fallacy. Our person assumes their source cannot be misinformed/mistaken, so after eliminating the possiblility that he is lying, she concludes that what he says must be true.

We can agree that we probably started with a trichotomy (or some other finite number of possibilities).

  1. Our source is lying
  2. Our source is mistaken
  3. Our source is correct

The first logical misstep that the person makes is assuming that our source cannot be mistaken and thus eliminating option 2, a clear example of Blind Loyalty Fallacy. This fallacy then causes what we could call a false dichotomy down the line, but the argument was clearly already ruined before this point.

Fallacies are incorrect lines of reasoning. At the point in the argument where we have eliminated the possibility that our source may be mistaken, it is in fact "logically sound" to assume the he must be correct since he isn't lying. Because of this, it would really be incorrect to call this a false dichotomy fallacy. The only real mistake in this person's argument was when he eliminated option 2 above, and thus it this is an example of a Blind Loyalty fallacy.

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  • The Blind Loyalty Fallacy is exactly what I was looking for. Thank you! – AntiMS May 20 '17 at 23:20
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Not sure why you are asking on this forum, not really related to philosophy, more game theory. This is related to or a variation on what is called in game theory as The Prisoner's Dilemma. A footnote Chapter 5 of Liars and Outliers: Enabling the Trust that Society Needs to Thrive by Bruce Schneier says:

The Prisoner's Dilemma was originally framed in the 1950s by Merrill Flood and Melvin Dresher at the RAND Corporation, and was named several years later by Albert Tucker. Many researchers have informed and analyzed this game, most famously John Nash and then Robert Axelrod, who used it to help explain the evolution of cooperation.

later in the same chapter it says:

Basic commerce is another type of Prisoner's Dilemma, although you might not have thought about it that way before. Cognitive scientist Douglas Hofstader liked this story better than prisoners, confessions, and jail time.

'Two people meet and exchange closed bags, with the understanding that one of them contains money, and the other contains a purchase. Either player can choose to honor the deal by putting into his or her bag what he or she agreed, or he or she can defect by handing over an empty bag.'

Very good book with numerous examples and variations and very good Bibliography.

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  • ...what? this question as stated has nothing to do with game theory or the Prisoner's Dilemma. It is about a particular example of a flaw in reasoning... i.e. a logical fallacy. Definitely belongs in this forum. – Andrew J. Kromkowski May 18 '17 at 16:07

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