Post hoc ergo propter hoc is Latin for "after this, therefore because of this." It is often shortened to simply post hoc.

Post hoc, also known as "coincidental correlation," 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:

• If event A causes event B, then A must have occurred before B.
• Event A occurred before event B.
• Therefore, A must have caused B.

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)."

See also

• regression fallacy
• non sequitur
• non causa pro causa

External links

• Post hoc fallacy in the Skeptic's Dictionary by Robert T. Carroll
• Post Hoc, Ergo Propter Hoc in the Fallacy Files by Gary N. Curtis
• Non Causa Pro Causa in the Fallacy Files by Gary N. Curtis