No True Scotsman

In plain terms

Someone makes a sweeping claim about a group. Someone else produces a member of that group who breaks the claim. The first person, rather than revising the claim, narrows the definition of "the group" until the counterexample no longer qualifies. The claim survives, because it's now a claim about a smaller group, one cleverly shaped to exclude anyone inconvenient.

The name comes from a classic example. "No Scotsman puts sugar on his porridge." "My uncle is a Scotsman and he puts sugar on his porridge." "Well, no true Scotsman puts sugar on his porridge."

Why it's fallacious

The original claim was about Scotsmen. The defense silently redefined Scotsman to mean "someone who doesn't put sugar on his porridge." The claim is now true by construction, because anyone who would falsify it has been defined out of the category. But it's also no longer informative. The claim says nothing about actual Scottish people, only about a category the speaker has gerrymandered into agreement.

The move is especially common with identity groups, ideologies, and religions: "No real X would ever..." every time an X does.

Canonical example

A: "A real programmer would never use an IDE. They'd write everything in a plain text editor."

B: "Linus Torvalds uses an IDE for some things."

A: "Then he's not a real programmer when he's doing that."

The claim started as a statement about programmers. When a clear counterexample arrived, the defense was to redefine "real programmer" to exclude the counterexample. The category has now been engineered to make the claim true by definition, which is the same as making it say nothing.

Counter-example (not a fallacy)

A: "A journalist publishes verifiable work under their name and submits to editorial review."

B: "Someone who publishes anonymous, unverifiable rumors on a blog calls themselves a journalist."

A: "That person isn't practicing journalism by any standard definition. The definition existed before the counterexample showed up."

This isn't no true Scotsman. The definition was established ahead of time and applies consistently. The fallacy requires the redefinition to happen in response to the counterexample. Pre-existing criteria that someone fails are just criteria. Criteria that emerge right when a counterexample arrives are the fallacy.

How to respond when you see it

Ask for the definition before the counterexample was raised. "What are the criteria for a 'real' X, written down in advance, that would apply to everyone equally?" If the criteria can only be named after the counterexample is known, they were reverse-engineered to exclude it. That's the fallacy showing itself.