Ad Hominem

In plain terms

An ad hominem happens when someone responds to an argument by attacking the person making it, rather than engaging with what was actually said. "You're wrong because you're an idiot" is the template.

The phrase is Latin for "to the person." It points at the target of the response: the arguer, not the argument.

Why it's fallacious

An argument either works or it doesn't based on its premises and its reasoning. The character, profession, motives, or hygiene of the person delivering it doesn't change whether the logic holds.

If a known liar says it's raining, that isn't proof it's dry outside. Check the window.

Canonical example

"Of course you'd say that minimum wage should be raised. You've never run a business in your life."

The response doesn't address the wage argument at all. It claims the speaker isn't qualified to hold the view, which is a comment on the person, not the position. The argument about minimum wage stands or falls on its economics, not the arguer's resume.

Counter-example (not a fallacy)

"You claim you saw the crash firsthand. Court records show you weren't in the state that day."

This looks like a personal attack, but it isn't ad hominem. The argument depends on the speaker's testimony, so challenging their credibility is directly relevant. Attacking a witness's reliability is fair game when the claim rests on their witnessing.

The line to watch: is the argument about the person, or does the argument require the person to be trustworthy? The second case is legitimate.

How to respond when you see it

Restate the original argument without the person attached to it. "Set me aside. The claim is X. What's wrong with X?" If the reply is still about you, the other side doesn't have an answer to the claim.