No True Scotsman
Version 1.0.0 · Updated 2026-07-30
CORE DEFINITION
When a counterexample appears, the original claim is quietly qualified with "true" to exclude the counterexample ("No true Scotsman would do that"), constituting the fallacy of appeal to purity.
SCAFFOLDING EFFECT
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No true Scotsman, or appeal to purity, is an informal fallacy in which one modifies a prior claim in response to a counterexample by asserting the counterexample is excluded by definition. Rather than admitting error or providing evidence to disprove the counterexample, the original claim is changed…
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When a universal assertion is refuted by a specific counterexample, the defender does not abandon the assertion but instead expels the counterexample from the group ("He is not a true X"), relying on a post hoc contraction of the definition to preserve the conclusion. This is a sophistry that uses definitional change to evade falsification (moving the goalposts).
MINIMUM ACTION
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Source support: Explicit
- en.wikipedia.orghttps://en.wikipedia.org/wiki/No_true_Scotsmanverified
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