[PatrickHenry]

It may be that the "No True Scotsman" fallacy is related to this "Accident" fallacy. The mistaken one declares (committing the fallacy of accident): "No Scotsman puts syrup on his haggis." When presented with the example of Angus MacPherson, who always puts syrup on his haggis, the mistaken one should simply recognize that he was wrong. But if he won't, then he compounds his original fallacy, and claims: "[Harrumph!] No true Scotsman puts syrup on his haggis."

[longshadow]

It may be that the "No True Scotsman" fallacy is related to this "Accident" fallacy. The mistaken one declares (committing the fallacy of accident): "No Scotsman puts syrup on his haggis."

Well, to be an example of the "Accident" Fallacy, there would have to be a preceding line of reasoning (which isn't there): "Andrew, Robert, and Charles are Scotsman; Andrew, Robert, and Charles don't put syrup on their haggis. Therefore, No Scotsman puts syrup on his haggis.....

But in the "No True Scotsman," the assertion is originally made gratuitously, hence it isn't the "Accident Fallacy".

I still believe it's a combination of equivocation ("Scotsman" is quickly redefined as "true Scotsman" to avoid refutation, which is clearly an example of equivocation) and petitio principii (one assumes that no real Scotsman wouls put syrup on his haggis in order to justify the equivocation of who is, or is not, a "Scotsman."