Post hoc, ergo propter hoc
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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."
 Form of the argument
- X happened before Y
- Therefore, X caused Y
 Other examples
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!"
An example is the following statement: "In Romania, abortion was illegal under two decades of rule by the 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." Just because the breast cancer rate went down does not mean that the illegality of abortions caused it. (Also, thanks for praising a commie, guys!)