Definition of fallacy
2a : 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
The fallacy of their ideas about medicine soon became apparent.
<the once-common fallacy that girls just weren't any good at math>
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
First Known Use: 14th century
FALLACY Defined for English Language Learners
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
Definition of fallacy for Students
1 : a false or mistaken idea
2 : false reasoning
Learn More about fallacy
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