fal·​la·​cy | \ ˈfa-lə-sē How to pronounce fallacy (audio) \
plural fallacies

Essential Meaning of fallacy

1 : a wrong belief : a false or mistaken idea popular fallacies about medicine It's a fallacy (to believe) that the Earth is flat.
2 : the quality of being false or wrong The fallacy of their ideas about medicine soon became apparent.

Full Definition of fallacy

1a : 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.
2a : 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.

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 In fact, some critics go as far as calling the industry’s craving for marijuana’s most popular cannabinoid a fallacy. Igor Dunaevsky, Rolling Stone, 10 Dec. 2021 While some people believe that the legacy consumer printer category is uninteresting and dreary, HP continues to prove that fallacy wrong. Mark Vena, Forbes, 27 Oct. 2021 This was a textbook example of the fallacy of stacking a bunch of same-same ingredients on top of each other. Soleil Ho, San Francisco Chronicle, 2 Dec. 2021 Concurrent hyperinflation has made Venezuela’s currency virtually worthless, and food security is a fallacy. The New Yorker, 25 Nov. 2021 Adele is trying to teach you an economics lesson in the sunk-cost fallacy. Natalie Lin, Vulture, 20 Nov. 2021 That fantasy ranks right up there with the gambler’s fallacy. Neil Senturia, San Diego Union-Tribune, 22 Nov. 2021 The second fallacy is in blaming renewables for failing to deliver on their promise and potential. Vasuki Shastry, Forbes, 15 Oct. 2021 The fallacy of a smile is the core essence of Faces. Donna-claire Chesman, Vulture, 15 Oct. 2021

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'fallacy.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

See More

First Known Use of fallacy

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

History and Etymology for fallacy

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

Learn More About fallacy

Time Traveler for fallacy

Time Traveler

The first known use of fallacy was in the 15th century

See more words from the same century

Dictionary Entries Near fallacy



fallacy of accident

See More Nearby Entries 

Statistics for fallacy

Last Updated

24 Dec 2021

Cite this Entry

“Fallacy.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/fallacy. Accessed 20 Jan. 2022.

Style: MLA
MLACheck Mark Icon ChicagoCheck Mark Icon APACheck Mark Icon Merriam-WebsterCheck Mark Icon

More Definitions for fallacy


fal·​la·​cy | \ ˈfa-lə-sē How to pronounce fallacy (audio) \
plural fallacies

Kids Definition of fallacy

1 : a false or mistaken idea
2 : false reasoning

More from Merriam-Webster on fallacy

Nglish: Translation of fallacy for Spanish Speakers

Britannica English: Translation of fallacy for Arabic Speakers

Britannica.com: Encyclopedia article about fallacy


Test Your Vocabulary

Difficult Spelling Words Quiz

  • alphabet pasta spelling help
  • Which is the correct spelling?
True or False

Test your knowledge - and maybe learn something along the way.

Universal Daily Crossword

A daily challenge for crossword fanatics.

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!