Post hoc ergo propter hoc

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Post hoc ergo propter hoc is Latin for "after this, therefore because of this." It is often shortened to simply post hoc. Some philosophy books translate the Latin to simply: "If, then therefore, because."

Post hoc, also known as "coincidental correlation" or "false cause," is a logical fallacy which assumes or asserts that if one event happens after another, then the first must be the cause of the second. It is a particularly tempting error because temporal sequence is integral to causality — it is true that a cause always happens before its effect. The fallacy lies in coming to a conclusion based only on the order of events, which is not an accurate indicator. That is to say, it is not always true that the first event caused the second event.

Post hoc is an example of affirming the consequent. It can be expressed as follows:

Event A occurred before event B.
Therefore, A must have caused B.

Example:

A rooster always crows prior to sunrise
Therefore: the rooster's crowing causes the sun to rise.

Another example:

Ice cream sales elevate greatly each June
Car thefts elevate each July.
Therefore: more people eating ice cream causes more cars to be stolen.

This line of reasoning is the basis for many superstitious beliefs and magical thinking, connecting two things that have no actual or logical connection. For example, if a person sees a coin on the ground and picks it up, and later receives good news, that person may become convinced that finding the coin resulted in the good news, even though it was a mere coincidence.

Post hoc reasoning is related to the logical fallacy "correlation implies causation (cum hoc ergo propter hoc)."

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