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Texas Sharpshooter Fallacy

September 25th, 2009

Taxonomy – Where am I?

Texas Sharpshooter Fallacy

classification : informal – non causa pro causa

Using the same data to both construct and test a hypothesis. A data mining fallacy and pattern recognition error where the arguer makes an ad hoc conclusion from a set of unrelated data without looking for corroborating data.

Foundations

Its name comes from a parable where a Texan fires his gun at the side of a barn, then paints a target around the shots and claims to be a sharpshooter. A hypothesis must be constructed before data is collected based on that hypothesis. If one data set is used to construct a hypothesis, then a new data set must be generated (ideally, in a different way, based on predictions made by the hypothesis) to test it.

Examples

This fallacy is often found in modern-day interpretations of the quatrains of Nostradamus. Nostradamus’s quatrains are often liberally translated from the original (archaic) French, stripped of their historical context, and then applied to support the conclusion that Nostradamus predicted a given modern-day event, after the event actually occurred.

Other Names

Confirmation bias
Cum hoc ergo propter hoc
Post hoc ergo propter hoc
Correlative based fallacies
Moving the goalpost, a related fallacy used to obtain the opposite conclusion.

Categories: Logic
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