What type of fallacy is this?

  • [1]. John says: "People are getting shorter"

    [2]. Mary says: "I will classify Johns claim as an outright lie, because people have been increasing in stature in the last 100 years, perhaps even longer that, this is a universally accepted fact amongst growth researchers"

    [3]. Bob says: "Mary's classification is false, because there MAY BE some indication that in the last year people may have gotten shorter, therefore you cannot classify it as an OUTRIGHT LIE"

My question is about BOB. I'm sure his reasoning is flawed because he employs a 'Fallacy of Exception': he discards a clear trend, not because of a proven break in the trend but because of a POSSIBLE break in the trend.

My 1st question: what is this type of fallacy called, precisely? I thought about 'reverse generalisation' but I can't find anything about that. I think Mary is right: John is telling an outright lie.

The mistake John makes is a sweeping generalisation without any proof and the proof we do have points in the exact opposite direction. So, Mary is right to call that a lie, especially because John doesn't specify a time period. Bob would be wrong in DEFENDING John with an exception, and defending John with a possible exception makes Bob even more wrong.

My 2nd question: Do you agree with me?

edit: For the sake of this question, let's assume that Mary is factually correct and that John has an ulterior motive for his claim (he sells small sized clothes or whatever) And yes, it's really true that on average people are getting taller, at least in the West.

  • Can you clarify what you mean by 'outright lie'? Does it only mean 'false' or also 'deliberate attempt to hide or manipulate the truth as conceived by others'?
    – user2953
    Jul 26, 2016 at 10:49
  • Agreement has not one iota of relevance to philosophy. You might appreciate the answer here to a similar question: meta.philosophy.stackexchange.com/questions/3040/…
    – MmmHmm
    Oct 22, 2016 at 0:21

2 Answers 2


I agree that John is mostly wrong based on facts. Assuming he does not have other motives he, himself, must be employing the fallacy of exception.

When Bob is defending him he is not defending his argument but his moral status. John was not lying, he was just wrong; his weak cognitive abilities and some indications that newborn kids are shorter formed his opinion.

Mary just got a bit swept away that's all.

From another point of view you can say that they are wrong because they did not follow Occam's principle stating that 'the argument with the fewest assumptions taken is most probably true'. I do not know what the negative of that is called.


Mary's argument is of course totally wrong. A lie is roughly speaking knowingly telling the untruth to deceive; making misleading but true statements may also be classified as lying.

But Mary doesn't give any evidence whatsoever that John knowingly says an untruth, and therefore no evidence whatsoever that John is a liar. Sure, it is a possibility, but Mary doesn't even give an argument. It seems that Mary doesn't know the meaning of "outright lie".

Bob's argument isn't very strong though. There is no need for any indications that people might get shorter. All that is needed is John misreading something, or misremembering something, to make his statement not a lie. John might have read one number in feet and inches, and another number in centimetres, and might have gotten the conversion wrong. That would be a silly mistake, but he wouldn't be a liar.

After your edit: Doesn't matter whether Mary is right or wrong. When discussing fallacies, we check whether logical reasoning is correct. Mary didn't give any reasoning whatsoever that supports her conclusion.

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