Post hoc ergo propter hoc

This article is about the logical fallacy. For other uses, see Post hoc.
For the West Wing episode, see Post Hoc, Ergo Propter Hoc (The West Wing).

Post hoc ergo propter hoc (Latin: "after this, therefore because of this") is a logical fallacy (of the questionable cause variety) that states "Since event Y followed event X, event Y must have been caused by event X." It is often shortened to simply post hoc fallacy. It is subtly different from the fallacy cum hoc ergo propter hoc ("with this, therefore because of this"), in which two things or events occur simultaneously or the chronological ordering is insignificant or unknown. Post hoc is a particularly tempting error because temporal sequence appears to be integral to causality. The fallacy lies in coming to a conclusion based solely on the order of events, rather than taking into account other factors that might rule out the connection.

The following is a simple example:

The rooster crows immediately before sunrise; therefore the rooster causes the sun to rise.


The form of the post hoc fallacy can be expressed as follows:

  • A occurred, then B occurred.
  • Therefore, A caused B.

When B is undesirable, this pattern is often extended to the inverse: Avoiding A will prevent B.


Popular culture

The phrase was the title of the second episode of West Wing, the multi-Emmy Award winning drama by Aaron Sorkin.[3]

An abbreviation of this phrase, "Post Hoc...", is used as the title of season six episode thirteen of Crossing Jordan. [4]

The phrase is used by the character Sheldon Cooper played by Jim Parsons 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.[5]

See also


  1. Damer, T Edward (1995). Attacking Faulty Reasoning: A Practical Guide to Fallacy-Free Arguments (3rd ed.). Belmont, CA: Wadsworth Publishing. p. 131. ISBN 978-0-534-21750-1. OCLC 30319422.
  2. Top 10: Football superstitions to rival Arsenal's Kolo Toure by Sandy Macaskill, The Daily Telegraph 25 February 2009
  3. "The West Wing". IMDB. Retrieved 3 February 2016.
  4. "Crossing Jordan: Post Hoc...". IMDB. Retrieved 3 July 2016.
  5. "The Big Bang Theory".
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