No true Scotsman

Knowing a name of a fallacy doesn't mean you understood what the fallacy means.

The No true Scotsman fallacy is a very specific thing and it doesn't mean what you think it does.

Here's the name-giving example of the No true Scotsman fallacy:

• Person A states an absolute statement: "No Scotsman puts sugar in his porridge."
• Person B disproves that by offering a counter-example "Angus is a Scotsman and he puts sugar in his porridge."
• Person A declares "But no true Scotsman puts sugar in his porridge."

So for an argument being the No true Scotsman, there need to be three elements. If one or more are missing, the fallacy doesn't apply:

• Person A does not retreat from the original statement
• Person A offers a modified assertion that excludes all counter-examples by definition (this turns the argument into a tautology: "No true Scotsman puts sugar in his porridge, and a true Scotsman is a Scotsman who does not put sugar in his porridge."
• Person A uses rhetoric to signal that change

So why does the no true Scotsman fallacy not apply here?

Because it's about this change, not about whether something can be classified as something.

Take for example this exchange:

• Person A: "A true Scotsman is someone who lives in Scotland, holds a Scottish passport and identifies as a Scotsman."
• Person B: "But Angus, who was born in the USA, and holds an US passport and who's only connection to Scotland is that his great grandma was from there claims that he is a true Scotsman."
• Person A: "He can claim what he want, he is no true Scotsman."

In this case Person A

• Did not retreat from the original statement
• Did not modify the original statement
• Did not use rhetoric to signal a change, because no change existed.

That's what @Demdaru@lemmy.world argued:

• A true Christian is someone who follows the teachings of Christ.
• American "Christians" claim to be Christians but are largely against the teachings of Christ.
• Hence they are no true Christians.

The "no true scotsman" fallacy is about changing your argument into a non-falsifiable tautology. It's not about using the words "true" or excluding some group from some definition. And it certainly doesn't mean "Everyone who calls themselves X surely and irrefutably belongs to group X".