Post hoc, ergo propter hoc

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Post hoc, ergo propter hoc is a Latin phrase for "after this, therefore, because of this." The term refers to a logical fallacy that because two events occurred in succession, the former event caused the latter event.[1][2]

In addressing a post hoc, ergo propter hoc argument, it is important to recognise that correlation does not equal causation.

Magical thinking is a form of post hoc, ergo propter hoc fallacy, in which superstitions are formed based on seeing patterns in a series of coincidences. For example, "these are my lucky trousers. Sometimes good things happen to me when I wear them."


[edit] Alternate names

  • assuming the cause
  • Faulty Causal Assumption
  • post hoc

[edit] Form of the argument

P1: X happened before Y.
P2: (unstated) Something which happens before something else must have caused it.
C1: Therefore, X caused Y.

[edit] Other examples

Many superstitions use this. For instance, a black cat crosses my path on the way to school. I then fail a test that day. If I used this fallacy, I may conclude I failed because of the black cat, while ignoring other factors as the amount of time I spent studying.

  • The rooster crows before sunrise, therefore the crowing rooster causes the sun to rise.
  • The drunk scientist conducts an experiment to see why he gets hangovers. He decides to keep a diary. Monday night, scotch and soda; Tuesday morning, hangover. Tuesday night, gin and soda; Wednesday morning, hangover. Wednesday night: vodka and soda; Thursday morning, hangover. Thursday night, rum and soda; Friday morning, hangover. On Friday night before going out for a drink, the drunk scientist has an epiphany. "Aha!" he says to himself, "I've got it! Soda causes hangovers!"
  • In the immortal words of Andrew Schlafly: "In Romania, abortion was illegal under two decades of rule by the communist dictator Nicolae Ceausescu, and the country enjoyed one of the lowest breast cancer rates in the entire world during that time, far lower than comparable Western countries."[3] (Just because the breast cancer rate went down does not mean that the illegality of abortions caused it.)

[edit] See also

[edit] External links

[edit] Footnotes

  1. Glenn, Cheryl; Loretta Gray. Hodges' Harbrace Handbook. 16th ed. Thomson: Boston, 2007: p. 480.
  2. The Fine Art of Baloney Detection, Carl Sagan
  3. Strange bedfellows.

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