Fallacy
noun /ˈfæl.ə.si/ — A mistaken belief based on unsound reasoning
Definition
A mistaken belief — or, in logic, an argument that appears valid but contains an error in reasoning. The word for the mistake that masquerades as sense.
Beyond the definition
Error that feels like logic. Fallacies are persuasive precisely because they use the form of good reasoning without its substance — they feel true even when they aren't.
Origin & history
From Latin 'fallacia' (deception, trick) — from 'fallax' (deceptive) — from 'fallere' (to deceive, to fail). Related to 'false', 'fail', and 'fault'. The deception that errors produce.
Example sentences
Illustrative sentences for learning, not verified community posts or sourced quotations.
The naturalistic fallacy: assuming that because something is natural, it is good. Arsenic is natural.
Identifying a fallacy doesn't win an argument — but it does clarify where the argument has gone wrong.
Some fallacies are structural (ad hominem, straw man); some are more subtle. The subtle ones are the dangerous ones.
How to use it
This entry uses a noun. Follow the examples for articles and singular or plural forms; not every noun takes “a” or “an.”
Choose “Fallacy” when the meaning fits your context: A mistaken belief — or, in logic, an argument that appears valid but contains an error in reasoning. The word for the mistake that masquerades as sense.
Synonyms
error, misconception, illusion, delusion, false belief
Antonyms
truth, validity, sound reasoning
Related words
Word in the Wild
See how this word appears in life, language and stories.
Illustrative sentences and imagined stories for learning — not verified sightings, interviews, or sourced quotations.
Fictional scene
Debate at Crossroads
Two people argue intensely at a crossroads, where one points to a path that leads into an illusory light.
The choice of a path that appears valid but may be misleading serves as a conceptual representation of a fallacy, an error in reasoning masquerading as sense.
Image credit: Wordspun · AI-generated conceptual illustration
Questions about this word
What does "Fallacy" mean?
Fallacy is noun meaning: A mistaken belief based on unsound reasoning. A mistaken belief — or, in logic, an argument that appears valid but contains an error in reasoning. The word for the mistake that masquerades as sense.
Where does the word "Fallacy" come from?
From Latin 'fallacia' (deception, trick) — from 'fallax' (deceptive) — from 'fallere' (to deceive, to fail). Related to 'false', 'fail', and 'fault'. The deception that errors produce.