What "ad hominem argument" actually means

One of the most misunderstood terms used in formal and informal logic is the concept of an "ad hominem" argument (or "attack").

Since "ad hominem" literally means "towards a person" or "against a person", many people believe that simply means "personal attack". After all, isn't that what it translates to? Which would mean that for example merely insulting someone is an "ad hominem"?

And that's how many people are often incorrectly using that term.

While "ad hominem attack" may technically speaking literally translate to "personal attack", the term is not used to mean just that, and has a much more specific meaning.

An "ad hominem" (argument or "attack") refers to a fallacious argumentative tactic where it's not what someone is saying that's being criticized, but the person who is saying it. The intent is to erode the credibility of the person in order to make his argument sound less credible and reliable.

And it's that last part that's an important part of the definition of an "ad hominem" argument: It's not merely a personal attack, it's not merely an insult, it's not merely an attempt to belittle, demean or defame someone. It's an attempt to erode the credibility of what that person is saying by eroding the credibility of the person himself. It's trying to erode the credibility of his claims by pointing out something bad about the person (real or invented.)

In other words, "you shouldn't believe what he is saying because he is a bad person."

It's a particularly egregious tactic when the claim in question has absolutely nothing to do with what the person is being accused of. However, even if the two are somehow related, that can still make it a bona fide fallacious "ad hominem" argument.

In this day and age there's a perfect practical example of this tactic being used in real life, and it's being used all the time. And that's when far-leftist activists say things like "he's a transphobe fascist, don't listen to him", as a response to what someone is claiming.

An "ad hominem" argument is actually a subset of the more generic "poisoning the well" tactic. The difference between the two is that the latter is not restricted to undermining the credibility of a person in order to discredit what he's saying, but can cover a wider set of situations. An "ad hominem" argument is a particular form of "poisoning the well".