47. Post Hoc Ergo Propter Hoc

Post hoc ergo propter hoc, Latin for “after this, therefore because of this,” (also known as post hoc, false cause, coincidental correlation, or correlation not causation) is a logical fallacy that is committed by an argument that has the form: “Since event B followed event A, then event B must have been caused by event A.” The fallacy is in coming to a conclusion based solely on the order of the events.

Note 1:

The distinction of this fallacy from cum hoc ergo propter hoc (the subject of episode 24), is that in the latter the order of the events is not a factor in the fallacious claim that one event is the cause of the other.

Note 2:

Post hoc is a particularly tempting error because temporal sequence appears to be integral to causality.

Example:

The World Trade Centre towers collapsed later on the same day that two of them were hit by airplanes, therefore the collapse was caused by the airplanes.

The argument is an example of the post hoc ergo propter hoc fallacy because it relies solely on the order of the events, even being stretched to cover the collapse of the third building (WTC7) that wasn’t hit by a plane at all. The sequence of events might be useful as part of an explanation that included other supporting evidence of the supposed causality. However, the preponderance of evidence is that the supposed causal relationship does not exist. The argument also ignores the possibility that the impacts and the collapse both had a common cause rather than one causing the other. A competent police detective would normally investigate a crime by discovering motives by asking who stands to benefit from the crime, then by establishing that the suspect had the means, and finally, once a likely suspect has been uncovered, by close investigation to find evidence that directly links the suspect to the crime. But none of those steps were taken in this case and instead a narrative that accused the alleged culprits was presented later on the same day.

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