Firmitas

Logical fallacy: No True Scotsman
Revision 1
© 2011-2019 by Zack Smith. All rights reserved.

No True Scotsman

An arguer who wishes to maintain the proposition P will simply modify the definition of its subject (Scotsmen) to exclude the validity of the counterexample and maintain the goodness of the subject.

Its form
  • Proposition P identifies a type as having a characteristic e.g. that all Scotsmen are good.
  • An instance A of the type is contrary to P e.g. there exists a perverted Scotsman.
  • Therefore the arguer redefines the type to exclude instance A e.g. no true Scotsman is a pervert.

Example

We dislike the idea that a Republican might support atheistic ideas. Therefore no true Republican is an atheist.

Weaknesses

One needs only notice the redefinition and point out that, every time the arbitrary characteristic is at risk of being shown to be invalid, the arguer revises the subject definition rather than accept new evidence that requires a more diverse definition.


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