THE AD HOMINEM FALLACY FALLACY

One of the most widely misused terms on the Net is "ad hominem". It is most often introduced into a discussion by certain delicate types, delicate of personality and mind, whenever their opponents resort to a bit of sarcasm. As soon as the suspicion of an insult appears, they summon the angels of ad hominem to smite down their foes, before ascending to argument heaven in a blaze of sanctimonious glory. They may not have much up top, but by God, they don't need it when they've got ad hominem on their side. It's the secret weapon that delivers them from any argument unscathed.

In reality, ad hominem is unrelated to sarcasm or personal abuse. Argumentum ad hominem is the logical fallacy of attempting to undermine a speaker's argument by attacking the speaker instead of addressing the argument. The mere presence of a personal attack does not indicate ad hominem: the attack must be used for the purpose of undermining the argument, or otherwise the logical fallacy isn't there. It is not a logical fallacy to attack someone; the fallacy comes from assuming that a personal attack is also necessarily an attack on that person's arguments.

Therefore, if you can't demonstrate that your opponent is trying to counter your argument by attacking you, you can't demonstrate that he is resorting to ad hominem. If your opponent's sarcasm is not an attempt to counter your argument, but merely an attempt to insult you (or amuse the bystanders), then it is not part of an ad hominem argument.

Actual instances of argumentum ad hominem are relatively rare. Ironically, the fallacy is most often committed by those who accuse their opponents of ad hominem, since they try to dismiss the opposition not by engaging with their arguments, but by claiming that they resort to personal attacks. Those who are quick to squeal "ad hominem" are often guilty of several other logical fallacies, including one of the worst of all: the fallacious belief that introducing an impressive-sounding Latin term somehow gives one the decisive edge in an argument.

But enough vagueness. The point of this article is to bury the reader under an avalanche of examples of correct and incorrect usage of ad hominem, in the hope that once the avalanche has passed, the term will never be used incorrectly again.

A: "All rodents are mammals, but a weasel isn't a rodent, so it can't be a mammal."
B: "This does not logically follow. By your own argument, the set of rodents is a subset of the set of mammals; and therefore, a weasel can be outside the set of rodents and still be in the set of mammals."

Hopefully it should be clear that neither A's argument nor B's argument is ad hominem. Perhaps there are some people who think that any disagreement is an ad hominem argument, but these people shouldn't be allowed out of fairyland.

A: "All rodents are mammals, but a weasel isn't a rodent, so it can't be a mammal."
B: "This does not logically follow."

B's argument is less comprehensive, but still not ad hominem.

A: "All rodents are mammals, but a weasel isn't a rodent, so it can't be a mammal."
B: "This does not logically follow. You evidently know nothing about logic."

B's argument is still not ad hominem. Note that B directly engages A's argument: he is not attacking the person A instead of his argument. There is no indication that B thinks his subsequent attack on A strengthens his argument, or is a substitute for engaging with A's argument. Unless we have a good reason for thinking otherwise, we should assume it is just a sarcastic flourish.

A: "All rodents are mammals, but a weasel isn't a rodent, so it can't be a mammal."
B: "You evidently know nothing about logic. This does not logically follow."

B's argument is still not ad hominem. B does not imply that A's sentence does not logically follow because A knows nothing about logic. B is still addressing the substance of A's argument.

A: "All rodents are mammals, but a weasel isn't a rodent, so it can't be a mammal."
B: "You evidently know nothing about logic."

B's argument is, most probably, still not ad hominem. The word "evidently" indicates that B is basing his opinion of A's logical skills on the evidence of A's statement. Therefore, B's sentence is a sarcastic way of saying that A's argument is logically unsound: B is attacking A's argument. He is not attacking the person instead of the argument.

A: "All rodents are mammals, but a weasel isn't a rodent, so it can't be a mammal."
B: "You know nothing about logic."

Even now, we can't conclude that B's reply is ad hominem. It could well be, and probably is, the case that B is basing his reply on A's argument. He is not saying that A's argument is flawed because A knows nothing about logic; instead, he is using A's fallacious argument as evidence to present a new argument: that A knows nothing about logic.

Put briefly, ad hominem is "You are an ignorant person, therefore your arguments are wrong", and not "Your arguments are wrong, therefore you are an ignorant person." The latter statement may be fallacious, but it's not an ad hominem fallacy.

A: "All rodents are mammals, but a weasel isn't a rodent, so it can't be a mammal."
B: "This does not logically follow. And you're an asshole."

B is abusive, but his argument is still not ad hominem. He engages with A's argument. There is no reason to conclude that the personal abuse of A is part of B's argument, or that B thinks it undermines A's argument.

A: "All rodents are mammals, but a weasel isn't a rodent, so it can't be a mammal."
B: "You're an asshole."

B's reply is not necessarily ad hominem. There is no evidence that's his abusive statement is intended as a counter-argument. If it's not an argument, it's not an ad hominem argument.

A: "All rodents are mammals, but a weasel isn't a rodent, so it can't be a mammal."
B: "You evidently know nothing about logic. And you're an asshole."

Again, B's reply is not necessarily ad hominem.

A: "All rodents are mammals, but a weasel isn't a rodent, so it can't be a mammal."
B: "Fuck you."

Not ad hominem. B's abuse is not a counter-argument, but a request for A to cease the discussion.

A: "All rodents are mammals, but a weasel isn't a rodent, so it can't be a mammal."
B: "Well, you've never had a good grasp of logic, so this can't be true."

B's argument here is ad hominem. He concludes that A is wrong not by addressing A's argument, but by appealing to the negative image of A the person.

A: "All rodents are mammals, but a weasel isn't a rodent, so it can't be a mammal."
B: "Well, you're a moron and an asshole, so there goes your argument."

B's reply here is ad hominem and abusive.

A: "All rodents are mammals, but a weasel isn't a rodent, so it can't be a mammal."
B: "Well, you're a rodent and a weasel, so there goes your argument."

B's argument here might appear on superficial inspection to be sound, but it is in fact ad hominem. He is using the terms "rodent" and "weasel" in different senses to those used by A. Although he tries to make it appear that he is countering A's argument by invalidating one of the premises, he is in fact trying to counter A's argument by heaping abuse on A. (This might also be an example of an ad homonym argument.)

A: "All murderers are criminals, but a thief isn't a murderer, and so can't be a criminal."
B: "Well, you're a thief and a criminal, so there goes your argument."

Harder to call this one. B is addressing A's argument, but perhaps unwittingly.

A: "All rodents are mammals, but a weasel isn't a rodent, so it can't be a mammal."
B: "Wrong! If a weasel isn't a rodent, then it must be an insectivore! What an asshole!"

B's argument is logically fallacious, and he concludes with some gratuitous abuse, but nothing here is ad hominem.

A: "All rodents are mammals, but a weasel isn't a rodent, so it can't be a mammal."
B: "I'm sorry, but I'd prefer to trust the opinion of a trained zoologist on this one."

B's argument is ad hominem: he is attempting to counter A not by addressing his argument, but by casting doubt on A's credentials. Note that B is polite and not at all insulting.

A: "Listen up, asshole. All rodents are mammals, but a weasel isn't a rodent, so it can't be a mammal."
B: "Yet another ad hominem argument. Ignore this one, folks."

A is abusive, and his argument is fallacious, but it's not ad hominem. B's reply, ironically, is ad hominem; while he pretends to deal with A's argument, in using the term "ad hominem" incorrectly, B is in fact trying to dismiss the argument by imputing that A is resorting to personal attacks.

A: "Listen up, asshole. All rodents are mammals, and a lizard isn't a mammal, so it can't be a rodent."
B: "Yet another ad hominem argument. Ignore this one, folks."

A's argument is sound, and not ad hominem. B's reply is again ad hominem.

A: "B is a convicted criminal and his arguments are not to be trusted."
B: "Yet another ad hominem argument. Ignore this one, folks."

A's argument is ad hominem, since it attempts to undermine all of B's (hypothetical) arguments by a personal attack. B's reply is not ad hominem, since it directly addresses A's argument (correctly characterising it as ad hominem).

A: "All politicians are assholes, and you're just another politician. Therefore, you're an asshole."
B: "Yet another ad hominem argument."

If you accept the premises, A's argument is sound. Either way, from the given context, we cannot conclude that it is ad hominem: it's not an attempt to undermine B's (hypothetical) arguments by abusing him, but instead an attempt to establish that B is an asshole. B's reply is ad hominem, since by incorrectly using the term "ad hominem", he is trying to undermine A's argument by claiming that A is resorting to personal attacks.

A: "All politicians are liars, and you're just another politician. Therefore, you're a liar and your arguments are not to be trusted."
B: "Yet another ad hominem argument."

If you accept the premises, A's argument is sound; but I think most of us would sympathise with B and class it as fallacious, and ad hominem. This is because we do not accept the premise that all politicians are liars. There is a false premise that lies behind all ad hominem arguments: the notion that all people of type X make bad arguments. A has just made this premise explicit.

A: "All rodents are mammals, but a weasel isn't a rodent, so it can't be a mammal."
B: "That does not logically follow."
A: "*Sigh* Do I have to spell it out for you? All rodents are mammals, right, but a weasel isn't a rodent, so it can't be a mammal! What's so hard to understand???!?"
B: "I'm afraid you're mistaken. Look at it logically. If p implies q, then it does not follow that not-p implies not-q."
A: "I don't care about so-called logic and Ps and Qs and that stuff, I'm talking COMMON SENSE. A weasel ISN'T a mammal."
B: "Okay, this guy's an idiot. Ignore this one, folks."
A: "AD HOMINEM!!!! I WIN!!!!!"

Although the last line of B, taken out of context, might look ad hominem (and was seized upon as such by A), it should be clear that taken as a whole, B's argument is not ad hominem. B engaged thoroughly with A's argument. He is not countering A's argument by saying A is an idiot; on the contrary, having logically countered A's argument, and having seen A's reaction, he is arguing that A is an idiot.

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