Ad hominem is a Latin phrase that means “against the man.” It is considered a fallacy or error in reasoning because it tries to refute an argument by attacking the person making the argument rather than the argument itself. This is fallacious because an argument’s soundness has no relation to the character of the person making the argument. Kind, sweet people can be wrong, and mean, vicious people can be right.
Unfortunately, in their zeal to blot out any and all fallacies, some people (especially those who like to argue on the internet) are quick to label any personal criticism or insult as an “ad hominem” argument. Let me point out two things that are often mistaken for the ad hominem fallacy.
1. Criticism or insults
If I say, “Fred is an obnoxious, egotistical jerk,” I am not making an ad hominem argument. I could be defaming Fred’s character, or I could be declaring his actual flaws. But, either way, I am saying something about Fred, not Fred’s arguments. If I said, “Fred is wrong about the doctrine of purgatory because he is an obnoxious, egotistical jerk,” that would be an example of an ad hominem fallacy. Remember, mean people can be right, and nice people can be wrong.
Other times pointing out inconsistencies in someone’s position is mistaken for an ad hominem. For example, on May 25, 2016, I debated Raphael Lataster at the University of Sydney on the question “Does God exist?” At one point Lataster responded to my use of the kalam cosmological argument by saying that it relied on the A-theory of time, which is something that the majority of philosophers do not accept (although this is actually an overstatement, given that 26 percent of philosophers endorse the competing B-theory of time and over half do not accept either theory).
In my rebuttal I said it was ironic that Lataster rejected the kalam argument because the theory of time undergirding it is not accepted by a majority of philosophers; and yet he defends mythicism, or the claim that Jesus did not exist or we can’t know if he existed. Unlike the A-theory of time, which a sizable number of scholars accept, only a tiny fraction of scholars subscribe to mythicism. That’s because, as the agnostic scholar Bart Ehrman says, “the view that Jesus existed is held by virtually every expert on the planet” (Did Jesus Exist? 4).
Lataster responded by accusing me of engaging in “bad form” and implied that I used the ad hominem fallacy. But as I pointed out in my reply, I wasn’t saying that Lataster was wrong because he endorses mythicism. I was pointing out that just as Lataster would not consider it a sufficient rebuttal of his work on Jesus’ existence to say, “Well, you’re wrong because the experts disagree with you,” he should not rebut my argument for God by simply saying some experts disagree with one facet of my argument. We have to analyze evidence in order to get at truth, not merely tally the vote of experts.
Finally, many people mistake insults for ad hominem arguments, because in the process of refuting an opponent’s argument some arguers take an additional swipe at the intelligence of the person they are refuting. Such a person might say, “After looking at all the evidence against the theory, it’s amazing that someone as smart as Fred could believe something so moronic.” Remember, it is a fallacy to say someone is wrong because he is a moron. However, it is only rude, and not necessarily fallacious, to say someone is a moron because he is wrong about something.
At this point one could argue that, yes, being of low intelligence does not mean a person is automatically wrong. But it is enough to make us doubt if the person is right. Maybe we can just say their argument is probably wrong, or we shouldn’t trust its conclusion. But a person’s character or intelligence is relevant only when one is examining the truth of the premises in their argument, not the logic of the argument itself. This leads to the second thing that is often mistaken for an ad hominem argument.
2. Attacking credibility
A variant of the ad hominem argument that focuses specifically on a person’s credibility is poisoning the well. The term comes from John Henry Cardinal Newman in his Apologia Pro Vita Sua. The philosophers Copi and Cohen summarize it in their textbook Introduction to Logic:
The British novelist and clergyman Charles Kingsley, attacking the famous Catholic intellectual John Henry Cardinal Newman, argued thus: Cardinal Newman’s claims were not be trusted because, as a Roman Catholic priest, (Kingsley alleged) Newman’s first loyalty was not to the truth. Newman countered that this ad hominem attack made it impossible for him and indeed for all Catholics to advance their arguments, since anything that they might say to defend themselves would then be undermined by others’ alleging that, after all, truth was not their first concern. Kingsley, said Cardinal Newman, had poisoned the well of discourse (169).
Poisoning the well is a fallacy because a person’s background, be it religious as in Newman’s case, or any feature, does not inhibit the person’s ability to make a good argument. To return to my debate example, I would be guilty of poisoning the well if I had said, “Folks, I’m not sure you can take anything Raphael says seriously, given that he wrote a book called There Was No Jesus, There Is No God.” Good arguments attack premises or patterns of inference, not other people.
An argument’s logic can be examined without knowing who is making the argument. The classic argument “All men are mortal, Socrates is a man, Socrates is mortal” is valid whether it is recited by someone from a MENSA institution or someone from a mental institution. Therefore, attacking the intelligence or character of the person making the argument does nothing to refute its logic.
But it is not always fallacious to attack someone’s character or credibility in order to disprove what he is saying. If I were a prosecutor and the defense called a witness who has been shown to have lied numerous times already, it would not be a case of poisoning the well if I said, “Folks, I’m not sure you can take anything Mr. Smith says seriously given that he has shown himself to be a compulsive liar.” The truth of the premises in an argument, rather than it’s logic, can sometimes be known only through the testimony of others, including testimony from the person making the argument. If there is a reason to suspect the accuracy of that person’s testimony, then the whole argument becomes suspect. Even if an argument contains no errors or fallacies, it will fail if one of the premises is false.
In conclusion, an argument commits the fallacy of ad hominem only if it says that an argument’s conclusion is false solely because of something negative related to the arguer. Merely stating something negative about the person making the argument, or saying the argument implies something negative about that person, does not make something ad hominem. It’s possible that we may not believe a premise that an untrustworthy person gives us in an argument, but the logic of his argument stands or falls apart from his character.