Well He Would, Wouldn't He?

An ad hominem is an attempt to dismiss arguments by attacking the source (the person) giving the argument. While   in some instances, questions of personal conduct, character, motives, etc., are legitimate and relevant to the issue, ad hominem usually involves insulting or belittling one's opponent in order to invalidate his argument. This tactic is logically fallacious because insults and even true negative facts about the opponent's personal character have nothing to do with the logic of the opponent's arguments or assertions.

The Profumo Affair was a 1963 British political scandal named after John Profumo, Secretary of State for War. He had an affair with Christine Keeler, the reputed mistress of an alleged Russian spy, followed by lying in the House of Commons when he was questioned about it. He had met Christine Keeler at a party thrown by a guy named Lord Astor. During a related trial, Mandy Rice-Davies, a close friend of Keeler's, was told that Lord Astor had denied having ever met either one of them, she replied “Well, he would, wouldn't he?” This is an example of where an ad hominem could be legitimate because it does call in to question the validity of Lord Astor's testimony. Even if Lord Astor knew the girls, I don't think it would look very respectful for a Lord to be running around with callgirls or being involved in a national scandal.  

If there was a debate on drilling in the region and Advocate A argued that it might be damaging to the environment and Side B came back with, “You can't believe A because he's a womanizer and a heavy drinker.” That is a fallacy. It has no relevance in the argument. It is an attempt to distract from the subject. I believe this tactic is used when the opposing side has a weak argument.

In many cases, using ad hominem, has backfired on the side using it. A lot of political campaigns try this “mud-slinging” to turn voters against their opponent. Most pole's, however, show that using this type of campaigning...