noun

fallacy

/ˈfæləsi/ · say it: FAL·uh·see

a mistaken belief or flawed reasoning

In Debate & Persuasion

In more detail

1. (noun) a false or mistaken belief, or an idea that many people think is true but is not

2. (noun) a mistake in reasoning or logic that makes an argument invalid or weak

Examples

1. It is a common fallacy that sugar makes children hyperactive.
2. The argument contains a logical fallacy because it makes an unsupported jump from one idea to the next.

How to use fallacy

Fallacy refers to either a widespread false belief (sense 1) or a defect in logical reasoning that undermines an argument (sense 2). The logical sense is especially common in academic writing and philosophy. While often used interchangeably with 'misconception', fallacy more specifically emphasizes the logical or structural problem rather than mere ignorance.

Common phrases

common fallacy
logical fallacy
fundamental fallacy
expose a fallacy
fallacy in reasoning

Synonyms

misconception · false belief · error · flaw · delusion

Opposites

truth · fact

Word family

fallacious (adjective) · fallaciously (adverb)

A common mistake

Learners sometimes use 'fallacy' for any false statement, but it specifically denotes either a mistaken belief held by many people or a flaw in reasoning, not simply any lie or inaccuracy.

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