No True Scotsman Fallacy
Also known as: Appeal to Purity, Moving the Definition
What is No True Scotsman?
The No True Scotsman fallacy occurs when someone makes a universal claim, is presented with a counterexample, and then redefines the criteria to exclude that counterexample rather than accepting that the original claim was too broad. Instead of modifying their position, they protect it by adding ad hoc qualifications that were not part of the original statement.
Example
A discussion about dietary choices and health.
“No real health-conscious person eats fast food. / What about Dr. Smith? She eats fast food occasionally and is very healthy. / Well, no truly health-conscious person would eat fast food.”
When presented with a counterexample (a healthy person who eats fast food), the speaker redefines 'health-conscious' to exclude anyone who eats fast food, making the claim unfalsifiable. The goalposts for what qualifies as 'health-conscious' were moved to protect the original claim.
How to Spot It
- A universal claim is made about a group (all X are Y).
- When a counterexample is presented, the definition of the group is narrowed to exclude it.
- Words like 'real,' 'true,' or 'genuine' are inserted after the counterexample appears.
- The claim becomes unfalsifiable because any counterexample is defined away.
How to Counter It
- Point out that the definition was changed after the counterexample was presented.
- Ask for the specific criteria that define the group before discussing examples.
- Show that the revised definition was not part of the original claim.
- Demonstrate that the argument has become unfalsifiable — if no possible evidence can contradict it, it is not a meaningful claim.
Related Fallacies
Check your arguments for logical fallacies
Try the Fallacy Checker