fallacy

noun

fal·​la·​cy ˈfa-lə-sē 

plural fallacies

1

a

: a false or mistaken idea

popular fallacies

prone to perpetrate the fallacy of equating threat with capability

—C. S. Gray

b

: erroneous character : erroneousness

The fallacy of their ideas about medicine soon became apparent.

2

a

: deceptive appearance : deception

b

obsolete : guile, trickery

3

: an often plausible argument using false or invalid inference

Did you know?

Philosophers are constantly using the word fallacy. For them, a fallacy is reasoning that comes to a conclusion without the evidence to support it. This may have to do with pure logic, with the assumptions that the argument is based on, or with the way words are used, especially if they don't keep exactly the same meaning throughout the argument. There are many classic fallacies that occur again and again through the centuries and everywhere in the world. You may have heard of such fallacies as the "ad hominem" fallacy, the "question-begging" fallacy, the "straw man" fallacy, the "slippery slope" fallacy, the "gambler's" fallacy, or the "red herring" fallacy. Look them up and see if you've ever been guilty of any of them.

Synonyms

• delusion
• error
• falsehood
• falsity
• hallucination
• illusion
• misbelief
• misconception
• myth
• old wives' tale
• untruth

Examples of fallacy in a Sentence

The fallacy of their ideas about medicine soon became apparent.

the once-common fallacy that girls just weren't any good at math

Recent Examples on the Web

Unfortunately, this claim rests on the fallacy that neurons in the brain are like pixels on a screen. —Geoffrey Boynton, Discover Magazine, 8 Aug. 2024

Most importantly, seeing Frazier’s expansive artworks in the near collapse of an empire calls attention to the fallacies of American hubris: that our country may never tremble, or more arrogantly put, that a single leader might keep us afloat. —Shameekia Shantel Johnson, ARTnews.com, 7 Aug. 2024

Energy analysts frequently point out this idea is a fallacy, because the price US drivers pay for gas is highly dependent on the global oil market. —Ella Nilsen, CNN, 3 July 2024

But the plot twists are based on logical fallacies and require too much suspension of disbelief. —Kelly Lawler, USA TODAY, 12 June 2024

Word History

Etymology

Latin fallacia, from fallac-, fallax deceitful, from fallere to deceive

First Known Use

15th century, in the meaning defined at sense 2b

Phrases Containing fallacy

• pathetic fallacy

Kids Definition

fallacy

noun

fal·​la·​cy ˈfal-ə-sē 

plural fallacies

1

: a false or mistaken idea

2

: the quality or state of being false