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

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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

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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

She also had a close call with the sunk cost fallacy: the failure to disengage from a probably doomed pursuit because of the time already invested in it.

From Los Angeles Times ● Oct. 21, 2026

Anything less would be a fallacy, a dream of a world that we don’t, and might never, live in.

From Salon ● Oct. 2, 2026

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

It’s a common fallacy to envision these species as arranged in a straight line of descent, with Ergaster begetting Erectus, Erectus begetting the Neanderthals, and the Neanderthals evolving into us.

From "Sapiens: A Brief History of Humankind" by Yuval Noah Harari

In part, this is a response to the fallacies of narrative, or at least of narratives that are imposed.

From Los Angeles Times ● Oct. 20, 2026

Following along as he picks data fallacies apart is a lot of fun, and I can’t wait to read the whole book.

From The Wall Street Journal ● Jul. 14, 2026

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’s one of the great fallacies, it seems to me,” said Lee, “that time gives much of anything but years and sadness to a man.”

From "East of Eden" by John Steinbeck

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Related Words

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

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