# No true Scotsman

*Also called: Appeal to purity*

- **Cluster:** Values and premises — Hidden value claims doing the arguing
- **Page:** https://fallacy.wiki/fallacy/no-true-scotsman/
- **In Arabic:** https://fallacy.wiki/ar/fallacy/no-true-scotsman.md
- **Licence:** CC BY 4.0 — https://creativecommons.org/licenses/by/4.0/

## What it is

Redefining a category mid-argument to exclude any counterexample.

## In the wild

> No real engineer writes code like that.

## How to answer it

Fix the definition before looking at examples, and hold it fixed after.

## Origin and naming

Philosopher Antony Flew described the move in God & Philosophy (1966) and returned to it in Thinking About Thinking (1975), where his example became the name: the Scot who reads of a savage crime in Aberdeen and, rather than concede, shifts to 'no true Scotsman would do such a thing'.

## More places it shows up

- A member of the coding forum says professional developers never use tabs; shown a celebrated engineer who does, they reply that she 'isn't really a professional in the craft sense'.
- When the peaceful-demonstration story includes a few broken windows, the organizer insists those 'weren't actual marchers' — before anyone has asked who they were.
- A football fan claims no true supporter would leave the stadium early; the empty seats at minute 85 are reclassified as tourists.
- In a book club, a reader defends the genre against a bad review: the disappointing novel 'isn't real science fiction anyway'.

## How to spot it

- A counterexample appears and the category shrinks on the spot to stay safe.
- Notice the adjective doing the rescue: 'real', 'true', 'genuine', 'authentic' — inserted only after the fact.
- Ask for the membership criteria stated before the example, and the definition has already been quietly rewritten.

## Nearby

- [Definist fallacy](https://fallacy.wiki/fallacy/definist.md)
- [Special pleading](https://fallacy.wiki/fallacy/special-pleading.md)
- [Ad hoc rescue](https://fallacy.wiki/fallacy/ad-hoc-rescue.md)

## Read more

- [Wikipedia](https://en.wikipedia.org/wiki/No_true_Scotsman)

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From fallacy.wiki — a bilingual field guide to 91 logical fallacies, published by phi holdings. Licensed CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/): reuse freely with attribution to fallacy.wiki.