''Post hoc ergo propter hoc'' (
Latin
Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...
: 'after this, therefore because of this') is an
informal fallacy that states: "Since event Y ''followed'' event X, event Y must have been ''caused'' by event X." It is often shortened simply to ''post hoc fallacy''. A logical fallacy of the
questionable cause
The questionable cause—also known as causal fallacy, false cause, or ''non causa pro causa'' ("non-cause for cause" in Latin)—is a category of informal fallacies in which a cause is incorrectly identified.
For example: "Every time I go to sle ...
variety, it is subtly different from the fallacy ''
cum hoc ergo propter hoc'' ('with this, therefore because of this'), in which two events occur simultaneously or the chronological ordering is insignificant or unknown. Post hoc is a logical fallacy in which one event seems to be the cause of a later event because it occurred earlier.
''Post hoc'' is a particularly tempting error because correlation sometimes appears to suggest
causality. The fallacy lies in a conclusion based ''solely'' on the order of events, rather than taking into account other factors potentially responsible for the result that might rule out the connection.
A simple example is "the rooster crows immediately before sunrise; therefore the rooster causes the sun to rise."
Pattern
The form of the ''post hoc fallacy'' is expressed as follows:
:* A occurred, then B occurred.
:* Therefore, A caused B.
When B is undesirable, this pattern is often combined with the
formal fallacy In philosophy, a formal fallacy, deductive fallacy, logical fallacy or non sequitur (; Latin for " tdoes not follow") is a pattern of reasoning rendered invalid by a flaw in its logical structure that can neatly be expressed in a standard logic syst ...
of
denying the antecedent
Denying the antecedent, sometimes also called inverse error or fallacy of the inverse, is a formal fallacy of inferring the inverse from the original statement. It is committed by reasoning in the form:
:If ''P'', then ''Q''.
:Therefore, if not ...
, assuming the
logical inverse holds: Avoiding A will prevent B.
Examples
* A tenant moves into an apartment and the building's furnace develops a fault. The manager blames the tenant's arrival for the malfunction. One event merely followed the other, in the absence of causality.
* Brazilian footballer
Pelé blamed a dip in his playing performance on having given a fan a specific playing shirt. His play recovered after receiving from a friend what he was told was the shirt in question, despite it actually being the same shirt he'd worn during his poor performance.
* Reporting of coincidental
vaccine adverse events, where people have a health complaint after being vaccinated and assume it was caused by the vaccination.
See also
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Bibliography
# Woods, J. H., Walton, D. N. (1977). Post Hoc, Ergo Propter Hoc.
# Mommsen, J. K. F. (2013). Wider Das Post Hoc Ergo Propter Hoc - Primary Source Edition. United States: BiblioLife.
# Woods, J., Walton, D. (2019). Fallacies: Selected Papers 1972–1982. Germany: De Gruyter.
References
{{Time in philosophy
Causal fallacies
Latin logical phrases