ad hominem
The label for an attack on the person instead of the claim.
An ad hominem argument answers a person rather than a point: it treats the speaker’s character, motives, or circumstances as if they settled the issue. Write it in roman type as an established English phrase, not as a flourish for any rude remark. Disagreement is not ad hominem. A relevant fact about a speaker can be fair (the treasurer has a financial stake in the vote). The fault is using the person as a substitute for the argument.
Examples
UseCalling the chemist a coward does not answer the data. That is an ad hominem move.
AvoidHe was blunt in the meeting, so his case was ad hominem.
The Latin means “to the person.” You do not need the Latin on the page when personal attack is enough; keep ad hominem for the logical fault.