From what I’ve seen, most of the Intellectual Takeout audience values logic, and would like to see their fellow Americans resort to it more often.

However, it’s important to not only value logic, but to use it correctly.

With that in mind, I wanted to briefly address the logical fallacy most often referenced on our Facebook page, and probably Facebook in general—the dreaded “ad hominem”.

As most of you know, “ad hominem” is Latin for “against the man,” and is used to refer to an argument or response that is directed at a person rather than his or her position.

However, as philosophy professor Edward Feser reminds us on his popular blog, “not every ad hominem attack… involves a fallacious ad hominem.”    

First, he explains what is an ad hominem fallacy:

“Attacking a person involves a fallacy when what is at issue is whether some claim the person is making is true or some argument he is giving is cogent, and where the attacker either (a) essentially ignores the question of whether the claim is true or the argument cogent, and instead just attacks the person giving it (in which case we have a kind of red herring fallacy) or (b) suggests either explicitly or implicitly that the claim can be rejected false or the argument rejected as not cogent on the basis of some irrelevant purported fault of the person giving it (in which case we have a poisoning the well fallacy, or perhaps a tu quoque).”

Thus, in the case of (a), it would be an ad hominem fallacy for someone to respond to a person arguing against transgender bathroom rights by simply calling him a “transphobe.” Or, in case (b), if someone was arguing that human beings cause harmful climate change, it would be an ad hominem fallacy for another person to dismiss his arguments outright because he knew the man had watched “An Inconvenient Truth” at some point in the past and enjoyed it.  

But for the rest of his post, Feser summarizes and explains the following 5 cases where an ad hominem criticism of a person is legitimate and not fallacious:

1) “When determining whether someone’s testimony is likely to be reliable” (as in a courtroom).

2) “When evaluating his worthiness as a philosophical conversation partner.” (One should only humor trolls so much).

3) “When exposing the fraudulence of his public reputation for expertise on some matter” (perhaps, in some cases, when Hollywood stars attempt to promote themselves as experts on a political or social issue).

4) “When exposing performative self-contradictions associated with some philosophical position.” (E.g. When someone asserts that there is no truth, implying that “it is true that there is no truth.”)

5) “When noting that a person’s willingness to take certain views seriously is evidence of a corruption of his more sensibilities.” (The example Feser gives is of a hypothetical person who believes there are good arguments for torturing babies “for fun.”)

In discussions and debates, it’s ideal when people can evaluate each other’s claims based purely on their rational merits. But unfortunately, in an imperfect world, it’s sometimes necessary to resort to an ad hominem argument—and to remember that not all of them are fallacies.