Fallacy

An error in reasoning, especially an argument that seems better than it really is.

Also: fallacies, logical fallacy, informal fallacy, formal fallacy

What it means

The Internet Encyclopedia of Philosophy calls a fallacy "a kind of error in reasoning". Formal fallacies can be spotted from an argument's logical form alone, while informal fallacies, such as appeals to authority or attacks on the person, depend on content and context. Aristotle made the first known systematic study, listing thirteen ways an argument can merely appear to refute an opponent. Charles Hamblin later criticised textbook treatments as dogmatic and urged a return to Aristotle's focus on dialogue. Classical Indian logic developed a parallel theory: Nyāya philosophers classified hetvābhāsa, 'pseudo-reasons', such as a reason that does not reliably track its conclusion or one that actually supports the opposite.

The questions it belongs to

• 4.2.1 FallaciesWhen is a bad-looking argument actually bad?
• 4.2 Informal LogicWhy does formal logic tell you so little about whether an argument is any good?

Thinkers

• Aristotle
• John Locke
• Richard Whately
• Charles Hamblin

Traditions

• Greek & Roman
• Indian
• Analytic

To read

• A Letter Concerning Toleration — John Locke
• An Essay Concerning Human Understanding — John Locke
• Categories — Aristotle

Sources and further reading

• Fallacies (Internet Encyclopedia of Philosophy)
• Fallacies (Stanford Encyclopedia of Philosophy)
• Nyaya (Internet Encyclopedia of Philosophy)

Written by the Coordinates of Thought editors and checked against the sources above on 29 October 2026. Not peer-reviewed. How we write and check.

All terms in the glossary