Post hoc ergo propter hoc

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Post hoc ergo propter hoc, Latin for after this, therefore because of this, 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 often shortened to simply post hoc. Some philosophy books translate the Latin to simply: "If after, then therefore, because", it is also known as multicollinearity, coincidental correlation and false cause. Post hoc ergo propter hoc is a particularly tempting error because temporal sequence appears to be integral to causality — retrocausation, if it actually occurs at all, is something we do not appear to experience. 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.

Pattern

Post hoc is similar to affirming the consequent. It can be expressed as follows:

• When A occurs, B occurs.
• Therefore, A causes B.

Examples

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

or,

1. Ice cream sales elevate greatly each summer
2. The number of common colds lower greatly each summer.
3. Therefore: higher ice cream consumption cures the common cold.

or,

1. In autumn, leaves fall on the pavement.
2. Autumn is the season when cement pavements crack.
3. Therefore: the falling leaves crack the pavement.

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

• Ante hoc ergo propter hoc
• Cargo Cult
• Correlation implies causation
• Cum hoc ergo propter hoc
• David Hume
• Nocebo
• non sequitur
• Non causa pro causa
• Placebo (origins of technical term)
• Regression fallacy
• Straw man
• Thought experiment
• Sophism

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

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