Exposing PseudoAstronomy

December 7, 2009

Logical Fallacies: Argument from Personal Incredulity


In my continuing series on logical fallacies, this post is going to be about another fairly common fallacy, and one that is almost always used to negate a claim rather than support it: the Argument from Personal Incredulity.

What is the “Argument from Personal Incredulity” Fallacy?

Yet again, we have a fallacy whose name is fairly descriptive, so long as you know what “incredulity” means (“the state of being unable or unwilling to believe something”). In short, this fallacy is invoked when someone simply says, “I don’t believe that” and leaves the rebuttal there.

Example from Neil Adams, the Expanding Earth

Neil Adams is a relatively famous illustrator who is credited with – among other things – reviving Batman as a dark hero in the comic book world several decades ago. Separate from Adams’ comic book pursuits, he fancies himself an “amateur scientist” who has, among other things, completely re-written modern physics, all stemming from his disbelief in the Theory of Continental Drift (Earth’s crust being made of many plates that move around on a plastic aesthenosphere).

I have listened to three interviews that Neil Adams has given – one being on The Skeptics’ Guide to the Universe, another on Coast to Coast AM, and a third being on a podcast that had commercials so I stopped listening to it after that one episode. In all of the interviews, one of the main, founding points that Adams’ made as to why he started his re-writing of physics is that he simply doesn’t believe Earth’s crust can move around. He also states that he thinks that a planet with all the land masses on one side (as in Pangaea) would just look stupid and shouldn’t be able to happen.

That is an argument from personal incredulity — he ignores all evidence of continental drift, seafloor ages and spreading, evidence of Pangaea, and then of course the standard model of particle physics, simply by starting from the Argument from Personal Incredulity.

Example from Global Climate Change Deniers

I try to keep this blog apolitical, and I personally don’t think that global climate change should even be considered a political issue, but unfortunately these days it is. I have heard a few pieces of presumed evidence against human-caused global climate change that actually have some science behind them — this post is not meant to talk about them at all.

Rather, there are many on the anti-human-caused global climate change who start and end their arguments with, “Humans can’t possibly be responsible for global warming [sic] because Earth is too big of a system for us to have that great an effect on it.” Besides this (a) being not true, it is also (b) a rather simple argument from personal incredulity because they refuse to accept that something is possible, regardless of the evidence.

Final Thoughts

Woo-hoo! I did a Logical Fallacies post without broaching the subject of creationism. But anyway, the Argument from Personal Incredulity is another one that is incredibly easy to spot and I have seen almost everyone do it. Since becoming aware of it a year or so ago, I have tried very hard to avoid falling into the trap, though I probably have from time-to-time. It’s so easy for someone to make a claim you don’t agree with and say, “No, that’s wrong,” and leave it at that. I have even observed it when people have reviewed grants I’ve written, (start rant) stating that they don’t believe the work could be accomplished in the time stated despite me being already half-way done with it and the second half being exactly the same as the first (end rant). But now that you are aware of it, it should be simple enough to avoid using it in almost all cases.

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  1. Who was the economist who posted on his blog that astronomy was suspect because it kept invoking things smacking into other things when it couldn’t explain something? He cherry picked a list of solar system features (the moon, Uranus rotating on its side, etc.) that are explained by “worlds in collision”. It struck him as incredulous so many features in the solar system were explained by worlds in collision that he thought it was just a convenient excuse astronomers were coming up with… you know so they didn’t have to go “well, the means only god could do that!”

    It was enormously silly.

    Comment by Karl — December 8, 2009 @ 9:32 am | Reply

  2. Why do you always patronise anyone who doesn’t agree with you? It just makes you sound arrogant.

    Comment by technophobe — December 10, 2009 @ 5:01 am | Reply

  3. Science isn’t an opinion, technophobe. If someone doesn’t like a restaurant I like, there is no sense patronizing them. If someone wholly ignores overwhelming scientific evidence and employs a grab bag of logical fallacies to promote an ideological view, then it seems to me calling a spade a spade is entirely just.


    “I don’t think the limbs of albinos have magical properties and shouldn’t be hacked to death for limbs that have no magical properties science can detect.”

    “Why do you always patronise anyone who doesn’t agree with you? It just makes you sound arrogant.”

    Yeah, how dare people be so arrogant.

    Comment by Karl — December 11, 2009 @ 1:40 pm | Reply

  4. Listen to this


    (just click on “click here to stream”)

    It last for 2 hours but WELL worth it. and THEN discuss what science is opinion and what science is fact.

    Comment by techno??? — December 12, 2009 @ 5:24 am | Reply

  5. [...] conclusion that the vaccine probably wasn’t the cause of her condition with an argument from personal incredulity, telling her something along the lines of nothing else other than the vaccine could have caused her [...]

    Pingback by ‘Vaccine Epidemic’ book launch party invades my alma mater, part 3 » The Vaccine Times — March 12, 2011 @ 12:57 pm | Reply

  6. [...] as dense as it did. Granted, Spike in his own special way then tries to rip it to shreds through an argument from personal incredulity, but that’s somewhat beside the point for this [...]

    Pingback by Mercury’s Uniqueness Revealed by MESSENGER: Does It Mean a Recent Creation? « Exposing PseudoAstronomy — August 7, 2011 @ 11:20 pm | Reply

  7. I just had to comment, love how our author uses the argument from authority fallacy in his explanation of global warming “deniers”. He states those with different views are wrong because” Besides this (a) being not true”. Now come on, this is the argument from authority fallacy in spades and incidentally a fallacy employed when such individuals speak of a consensus of scientific opinion. For there are no consensus votes in the realm of true science. There is only proven fact of which he offers none.
    Next he “Staw mans” in his follow up statement. He incorrectly states the issue as “global warming” very few scientific minds would say global climate change does not happen. The key question has always been does human activity contribute significantly to changes in the earth’s climate. It is the inability of those who support the notion of significant anthropomorphic climate change, to pin said change solely to human activity while ignoring or down grading other possible causes for climate change, that some take issue. Some of those other possible causes include: variance in solar output, changes in volcanism, minor changes in the earth orbit and/or axis rotation.

    Comment by james — September 24, 2012 @ 5:12 pm | Reply

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