In my opinion, the most embarrassing grammatical mistake that one can make is to misuse the word ‘whom.’ On its face, this may seem counter-intuitive. After all, many people have trouble with the difference between who and whom; it’s one of the more challenging grammar concepts. But when someone uses whom incorrectly, it means that they tried to look smart but couldn’t pull it off. It wasn’t a thoughtless mistake; the offender put effort into the sentence and still messed up.

I mention this because I’ve started to notice a similarly embarrassing error made by people trying to flex their rhetorical and logical chops but who only betray their lack thereof. Many people mistakenly invoke the ad hominem fallacy. Here’s an example:

Guy 1: “All polo ponies are fast. My horse is fast, so my horse is a polo pony.” Guy 2: “You’re an idiot.” Guy 1: “Because you’ve resorted to ad hominem, you must be admitting that I’m right.”

The mistake that Guy 1 made was in thinking that all personal attacks are ad hominem. While insults may be indecorous, they are not fallacious. It is true that Guy 2’s response is not an adequate counter-argument, but there was no fallacy. In order to be an example of the ad hominem fallacy, the personal attack must be used to counter the person’s argument. Here’s a good example of the ad hominem fallacy:

Guy 1: “All polo ponies are fast. My horse is fast, so my horse is a polo pony.” Guy 2: “We all know that you’re an idiot, so your argument cannot be true.”

In this case, Guy 2 attacks Guy 1’s argument by attacking the man himself. This is a fallacy because the argument exists in isolation from the man, so attacks on Guy 1 don’t do anything to disprove the argument.

In order to be fallacious, the personal invective must be intended as evidence that the argument is wrong.