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Post hoc, ergo propter hoc

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An example observed in the wild
Part of the series on
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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."

Alternate names[edit]

  • Assuming the cause
  • Faulty Causal Assumption
  • Post hoc

Form of the argument[edit]

P1: X happened before Y.
P2: (unstated) Y was caused by something (that happened before Y).
C1: Therefore, X caused Y.

Other examples[edit]

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 such 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!"
  • When compared on a graph, the number of deaths by falling and drowning in a swimming pool correlates with the number of movies that Nick Cage is in. This is completely coincidental.. Unless it's not.[4]

See also[edit]

External links[edit]

References[edit]

  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.
  4. Cage movies and drowning, Tyler Vigen