Post hoc ergo propter hoc

Post hoc ergo propter hoc (Latin: "after this, therefore because of this") is a logical fallacy (of the questionable cause variety) that states "Since event Y followed event X, event Y must have been caused by event X." It is often shortened to simply post hoc fallacy. It is subtly different from the fallacy cum hoc ergo propter hoc ("with this, therefore because of this"), in which two things or events occur simultaneously or the chronological ordering is insignificant or unknown. Post hoc is a particularly tempting error because temporal sequence appears to be integral to causality. The fallacy lies in coming to a conclusion based solely on the order of events, rather than taking into account other factors that might rule out the connection.

The following is a simple example:

The rooster crows immediately before sunrise; therefore the rooster causes the sun to rise.

Pattern

The form of the post hoc fallacy can be expressed as follows:

• A occurred, then B occurred.
• Therefore, A caused B.

When B is undesirable, this pattern is often extended to the inverse: Avoiding A will prevent B.

Examples

• "I can't help thinking that you are the cause of this problem; we never had any problem with the furnace until you moved into the apartment." The manager of the apartment house, on no stated grounds other than the temporal priority of the new tenant's occupancy, holds that the tenant's presence has some causal relationship to the furnace's becoming faulty.^[1]
• In the obsolete theory of spontaneous generation, people once erroneously believed that maggots arose spontaneously from rotting meat, due to observing their presence at the site of rotting meat. Francesco Redi disproved this by using jars with lids permeable to air but not insects, compared to uncovered jars. The flies could only enter the uncovered jars and those were the only ones in which maggots appeared.
• Aluminium, barium, and strontium are being found in soil tests, and there are more airplane contrails seen in the sky. Therefore, the contrails must actually be chemtrails purposefully spraying these elements into the atmosphere.
• After smoke comes out of an electronic component, it no longer works. Therefore, the smoke was magic, and made the component work.
• The Brazilian footballer Pelé is said to have blamed a dip in form on having given a fan a specific playing shirt. Once back in possession of the shirt, he attributed his return in form to having retrieved the shirt. His fallacious reasoning was revealed by the subsequent discovery that the original shirt had not been recovered, but replaced by the same one he had worn the previous match.^[2]

Popular culture

The phrase was the title of the second episode of West Wing, the multi-Emmy Award winning drama by Aaron Sorkin.^[3]

An abbreviation of this phrase, "Post Hoc...", is used as the title of season six episode thirteen of Crossing Jordan. ^[4]

The phrase is used by the character Sheldon Cooper played by Jim Parsons in the third season of The Big Bang Theory. Sheldon mentions the logical fallacy in disputing his mother's claim that her prayer group did ensure his safety during his North Pole expedition.^[5]

See also

• Correlation does not imply causation
• Confirmation bias
• Superstition
• Jumping to conclusions
• Magical thinking
• Cargo cult
• Whig history
• Apophenia

References

Philosophy of time
Concepts in time	Time Duration A priori and a posteriori Eternity Event Action Deterministic system Free will Eternal return A-series and B-series Temporal parts Growing block universe Multiple time dimensions	Time Portal
Theories of time	Determinism Temporal finitism Fatalism Indeterminism Compatibilism and incompatibilism Presentism Eternalism Four dimensionalism Endurantism Perdurantism B-Theory of time
Related articles	Metaphysics Etiology Teleology Post hoc ergo propter hoc The Unreality of Time The Singular Universe and the Reality of Time