Attacking the person rather than the claim, which leaves the claim untouched.
"He's not a climate scientist, he's a geologist" leaves the argument untouched. It becomes legitimate only when the person's reliability is the actual question, as with a witness's record of perjury.
In practice
- "You would say that, you work for an oil company." The claim about emissions data is still either right or wrong.
- A reviewer dismisses a study because the author has a book to sell, without opening the methods section.
- Standing
- Not fallacious where the person's credibility is itself the matter at issue.
- Further reading
- Wikipedia
- Subject
- Decision-making & Reasoning
- Essay
- The catalogue of predictable errors