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fallacy

[fal-uh-see]
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noun, plural fal·la·cies.
  1. a deceptive, misleading, or false notion, belief, etc.: That the world is flat was at one time a popular fallacy.
  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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Origin of fallacy

1350–1400; < Latin fallācia a trick, deceit, equivalent to fallāc- (stem of fallāx) deceitful, fallacious + -ia -y3; replacing Middle English fallace < Middle French

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Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018


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British Dictionary definitions for fallacies

fallacy

noun plural -cies
  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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Word Origin for fallacy

C15: from Latin fallācia, from fallax deceitful, from fallere to deceive
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for fallacies

fallacy

n.

late 15c., "deception, false statement," from Latin fallacia "deception," noun of quality from fallax (genitive fallacis) "deceptive," from fallere "deceive" (see fail (v.)). Specific sense in logic dates from 1550s. An earlier form was fallace (c.1300), from Old French fallace.

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Online Etymology Dictionary, © 2010 Douglas Harper

fallacies in Culture

fallacy

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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The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.