fallacy

American  

[fal-uh-see] / ˈfæl ə si /

noun

• fallacies
  plural

1. a deceptive, misleading, or false notion, belief, etc..

   That the world is flat was at one time a popular fallacy.

   Synonyms:

   misapprehension, delusion, misconception

2. a misleading or unsound argument.

3. deceptive, misleading, or false nature; erroneousness.

4. Logic. any of various types of erroneous reasoning that render arguments logically unsound.

5. Obsolete. deception.

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fallacy British  

/ ˈfæləsɪ /

noun

1. an incorrect or misleading notion or opinion based on inaccurate facts or invalid reasoning

2. unsound or invalid reasoning

3. the tendency to mislead

4. logic an error in reasoning that renders an argument logically invalid

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fallacy Cultural  

1. A false or mistaken idea based on faulty knowledge or reasoning. For example, kings who have divorced their wives for failing to produce a son have held to the fallacy that a mother determines the sex of a child, when actually the father does. (See sex chromosomes.)

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Other Word Forms

Noun Inflected Forms

• fallacies
  plural

Etymology

Origin of fallacy

First recorded in 1350–1400; from Latin fallācia “a trick, deceit,” from fallāc- (stem of fallāx ) “deceitful” + -ia -y ³; replacing Middle English fallace, from Middle French

Explanation

A fallacy is a misleading argument or belief based on a falsehood. If you oppose state testing in schools, you think it is a fallacy that educational quality can be measured by standardized tests. Fallacy comes from the Latin fallacia, for deceit. It technically means a flaw in an argument that makes it deceptive or misleading. In poetry, the "pathetic fallacy" is the false idea that things like rocks or stars have human feelings (pathos). Fallacy can also be used more generally for any false statement or idea. Some synonyms are misconception and error.

Example Sentences

See Examples For:

fallacy fallacies

But we know too that to double down is to fall prey to the timeworn seduction of the sunk-cost fallacy: We’ve invested so much in this effort that to abandon it now would be worse.

From The Wall Street Journal ● Aug. 3, 2026

"This is the sunk cost fallacy," he said, adding that "it keeps the addictive behaviour loop".

From Barron's ● May 31, 2026

"I think the thing young founders get wrong is they view hours worked in and of itself as necessary and sufficient to think of themselves as productive. And that's where the fallacy lies", he explains.

From BBC ● Feb. 8, 2026

The sunk-cost fallacy tempts people to pay escalating premiums because they’ve paid for so long.

From MarketWatch ● Nov. 15, 2025

Fossils, for example, and whether their existence disproved the Book of Genesis; Brother Mendel’s experiments on the sexual reproduction of the sweet pea; the fallacy of laudable pus.

From "The Evolution of Calpurnia Tate" by Jacqueline Kelly

Even neomercantilists have a little point buried in a heap of fallacies.

From The Wall Street Journal ● Oct. 21, 2025

“One of the fallacies is that this is only targeting Latinos. If you look at the Vietnamese, Cambodian, Hmong, Chinese, even Japanese communities, they’re being picked up right in court.”

From Los Angeles Times ● Aug. 14, 2025

Ultimately, reframing the issue and zooming out can help counter the emotionally charged nature of these types of decisions that often lead to sunk cost fallacies.

From Salon ● Dec. 15, 2024

So placing that art outside time, or concocting fallacies about its artist’s intentions, has the potential to skew our perception of the art moving forward.

From Slate ● Sep. 1, 2024

It can conceal a dozen fallacies at once.

From "The Left Hand of Darkness" by Ursula K. Le Guin

Related Words

• deception
• falsehood
• heresy
• inconsistency
• misinterpretation
• paradox
• untruth