|No true Scotsman is a logical fallacy that is committed by the proponent of a universal claim who, when faced with a counterexample, modifies the subject of the claim to exclude the counterexample by rhetoric without reference to any objective rule.
The fallacy takes one of the following two alternative forms, where the person committing the fallacy is labelled “Tom”:
Tom: No A are B.
Tom: All A are B.
The term was coined by philosopher Antony Flew in his 1975 book Thinking About Thinking. Here is the canonical example given in the book:
The fallacy is similar to begging the question (episode 23) but with the difference that the conclusion is a modification of the subject of the initial claim so as to arbitrarily exclude a counterexample. Begging the question assumes the premise in the conclusion but does not modify it, and does not necessarily involve any counterexamples.
The fallacy is also similar to the overwhelming exception fallacy (discussed in the previous episode) insofar as both fallacies are committed in response to a counterexample but with the following difference: The overwhelming exception fallacy responds to the counterexample by acknowledging it by stating that the initial claim is “except for” the counterexample, and creating the false impression that the counterexample is insignificant. By contrast, the no true scotsman fallacy restates the initial claim in a way that fallaciously denies that the subject of the counterexample is a subject of the claim.