Ad hominem means “against the person” and refers to attacking the person rather than their argument. “Poisoning the well” is a form of ad hominem in which you discredit someone’s argument by connecting them with unpopular or immoral people (Nazis are often used) or traits.
The ad hominem argument is very common and easy to spot. It’s actually one I find hard to avoid completely. For instance, it’s really tempting to just say people who believe in homeopathy are stupid, rather than addressing why homeopathy doesn’t work.
I recently read an excellent example of the ad hominem attack on someone’s blog. This person was responding to Dr. Steven Novella’s appearance on Dr. Oz’s TV show. Dr. Oz sometimes supports pseudoscience on his show. He has said, ““It’s just that if we’re truly going to achieve maximum healing, maximum impact, we ought to take any tool that’s at our disposal, and that includes nonscientific approaches, as long as we have evidence that they don’t hurt the patients.” Dr. Novella was on the show to speak on behalf of science based medicine.
This blogger is apparently a big fan of Dr. Oz. His response to Dr. Novella was interesting. He took a three-pronged approach. First he attacked Dr. Novella’s hair. He thinks Dr. Novella wears a toupee, and a bad one at that. I don’t know whether he wears one or not (though people who know him say he doesn’t,) but I don’t see how someone’s hair or lack thereof has anything to do with the validity of their beliefs. How much hair you have is something out of your control so it’s kind of like criticizing someone’s height.
His second attack was on Dr. Novella’s credentials. He said the doctor was not really a professor at Yale University and only testified on behalf of insurance companies. It’s easy enough to go to the Yale University site and check out the truth. He’s an Assistant Professor of Neurology at Yale, is board certified in neurology, and got his M.D. from Georgetown University in 1991. Oh, and he’s accepting new patients (but I sincerely hope you don’t need a neurologist.) It baffles me how anyone could not think he is exactly who he says he is, unless they think Yale University and all of his medical colleagues are pulling off some big scam.
The blogger’s last argument was that Dr. Novella has had a homosexual affair with James Randi. Huh? Looks like classic poisoning the well, assuming that you think there is anything wrong with homosexuality or James Randi (of course I don’t, but apparently this blogger does.) Actually, I’d think that having an affair with James Randi would give you serious bonus points in the Skeptical world. One of the things that makes this especially odd is that if Dr. Novella was gay, I really think he’d have no problem at all with anyone knowing it. It might come as a surprise to his wife, though.
This was a classic example of how not to make a credible case for your position.