no true Scotsman fallacy
Noun
Meaning
no true Scotsman fallacy (plural no true Scotsman fallacies)
The logical fallacy of attempting to retain an unreasoned assertion by excluding the case given in a counterexample, as in: "No Scotsman puts sugar on his porridge." "I am Scottish, and I put sugar on my porridge." "Well, no true Scotsman puts sugar on his porridge."