Ad hominem is Latin for “to the man,” and occurs when a person overlooks the substance of an argument and instead attacks its source. Here’s an example:
“I think it’s best to decrease the amount you travel during the swine flu outbreak,” said Joe.
“Yeah, well, you’re an idiot.”
Is Joe an idiot? Even if that’s true, it doesn’t address the claim of his argument and is therefore fallacious. It doesn’t matter.
Any time a person “rebukes” an argument with claims against the individual making it, they’re using ad hominem propaganda: they are trying to divert attention away from the argument itself.
In fact, this is usually effective, for better or worse. In the case of a political campaign, for example, it might be fair to point out an opponent’s past political decisions as a rebuke against one of their proposals. It would be, in that sense, relevant to the overall discussion of who would make a better representative.
In most debates, however, you want to stay as far away from ad hominem attacks as possible. Not only does it take the focus away from the argument, it also decreases your own credibility.
To counter ad hominem propaganda, always respond to arguments with logical, reasonable claims. If someone uses ad hominem attacks against you, ignore them and move on.
For more information on ad hominem propaganda, click on over to Mission: Critical (Ad Hominem Introduction)