fallacy

noun fal·la·cy \ ˈfa-lə-sē \
Updated on: 10 Nov 2017

Definition of fallacy

plural fallacies
1 a obsolete : guile, trickery
b : deceptive appearance : deception
2 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.
3 : an often plausible argument using false or invalid inference

Examples of fallacy in a Sentence

  1. The fallacy of their ideas about medicine soon became apparent.

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

Recent Examples of fallacy from the Web

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.

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.

Origin and Etymology of fallacy

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


FALLACY Defined for English Language Learners

fallacy

noun

Definition of fallacy for English Language Learners

  • : a wrong belief : a false or mistaken idea

  • : the quality of being false or wrong


FALLACY Defined for Kids

fallacy

noun fal·la·cy \ ˈfa-lə-sē \

Definition of fallacy for Students

plural fallacies
1 : a false or mistaken idea
2 : false reasoning


Seen and Heard

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