Post hoc fallacy

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The post hoc fallacy means "after this, therefore because of this". Its Latin name is Post hoc ergo propter hoc. It is a logical fallacy. When event B happens after event A, a person might think "event A must have caused event B".[1]

Example:

  • The rooster crows immediately before sunrise.
  • Therefore the rooster causes the Sun to rise.

It is a tempting error because sequence in time does sometimes suggest causality.[2] When I press the light switch, the light comes on, and that is a cause and effect sequence. The difference is that it can be explained why the light comes on when the switch is pressed. On the other hand, no-one can explain why a rooster's crowing might affect the Sun.

Popular culture[change | change source]

The phrase is used by the character Sheldon Cooper in the third season of The Big Bang Theory. Sheldon mentions the logical fallacy in disputing his mother's claim that her prayer group did ensure his safety during his North Pole expedition.[3]

References[change | change source]

  1. Pinto, Robert. Argument, inference and dialectic: collected papers on informal logic. p. 56.
  2. Damer, T Edward 1995. Attacking faulty reasoning: a practical guide to fallacy-free arguments. 3rd ed, Belmont, CA: Wadsworth, p131. ISBN 978-0-534-21750-1.
  3. "The Big Bang Theory".