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Argument from Incredulity

(also known as:  argument from personal astonishment, argument from personal incredulity, personal incredulity)

Description: Concluding that because you can't or refuse to believe something, it must not be true, improbable, or the argument must be flawed. This is a specific form of the argument from ignorance.

Logical Form:

Person 1 makes a claim.

Person 2 cannot believe the claim.

Person 2 concludes, without any reason besides he or she cannot believe or refuses to believe it, that the claim is false or improbable.

Example #1:

Marty: Doc, I'm from the future. I came here in a time machine that you invented. Now, I need your help to get back to the year 1985.

Doc: I got enough practical jokes for one evening. Good night, future boy!

Explanation: Clearly Marty is making an extraordinary claim, but the doc's dismissal of Marty's claim is based on pure incredulity. It isn't until Marty provides the Doc with extraordinary evidence (how he came up with the Flux Capacitor) that the Doc accepts Marty's claim. Given the nature of Marty's claim, it could be argued that Doc's dismissal of Marty's claim (although technically fallacious) was the more reasonable thing to do than entertain its possibility with good questions.

Example #2:

NASA: Yes, we really did successfully land men on the moon.

TinFoilHatGuy1969: Yeah, right. And Elvis is really dead.

Explanation: The unwillingness to entertain ideas that one finds unbelievable is fallacious, especially when the ideas are mainstream ideas made by a reputable source, such as a NASA and the truthfulness of the moon landings.

Exception: We can't possibly entertain every crackpot with crackpot ideas. People with little credibility or those pushing fringe ideas need to provide more compelling evidence to get the attention of others.


Bebbington, D. (2011). Argument from personal incredulity. Think, 10(28), 27–28.

Registered User Comments

Sunday, October 06, 2019 - 06:29:31 PM
"when the ideas are mainstream ideas made by a reputable source, such as a NASA" = appeal to authority.

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Bo Bennett, PhD
Monday, October 07, 2019 - 07:08:04 AM
Appeal to authority is insisting that a claim is true simply because a valid authority or expert on the issue said it was true, without any other supporting evidence offered. I am not insisting the claim is true, but pointing out that the degree of fallaciousness is often correlated with the probability of the claim being true. More reliable sources are more likely to make true claims--this is by definition. Being incredulous of claims such as a flat earth are often the result of knowledge of facts that counter the claim being made, and the incredulousness is reason-based.

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Thursday, December 19, 2019 - 11:13:39 PM
@Bo Bennett, PhD: I find it rather odd that you're defending something that you clearly setup as such. I mean "NASA" vs "TinFoilHatGuy1969," the bias is clearly present from the start. You would not have picked "High School Dropout: Yes, we really did successfully land men on the moon." and "College Graduate: Yeah, right. And Elvis is really dead."

Of course, you could have fun with authority and mainstream ideas "Almighty Church: The earth is the center of the universe" "Crackpot Galileo: Uhh, you're wrong" which is always the issue with throwing such exceptions in... there are exceptions to the exception to the exception of the exception.

After all, most of classical philosophy is about questioning the foundations of knowledge, asking if the reasoning we've accepted as truth (and hence are incredulous to any radical ideas) is actually truth or something we've accepted as truth. No Cartesian skepticism, no allegory of the cave, simply a blind acceptance of what you sense or have been informed about.

Seemed to have found a little too much desire to defend my point here, which was simply that Mark was right, as the clear intent here was to create an easily defeated opponent; and in doing so you end up relying on informal fallacies of your own.

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