• What is Meant by ‘Ad Hominem’?


    If you’ve ever had an argument on the internet, you’ve probably had a discussion similar to this:

    Jill: “Blue is the best colour!”

    Jack: “You only think that because you’re an idiot.”

    Jill: “Address my point instead of engaging in ad hominems.”

    Jack: “That’s not ad hominem. That’s an insult. Ad hominem is when you say ‘it’s false that blue is the best colour because you’re an idiot’. I said that you’re an idiot, but I can give you other reasons why it’s false that blue is the best colour.”


    I think most people would agree with Jack, but I want to show that Jill is using ‘ad hominem’ correctly.


    A couple of years ago I was reading a paper1 about ‘Genuine Modal Realism’ in which the author made what they called “an ad hominem point” against the philosopher David Lewis (a leading proponent of GMR). The point in question (I think) was that some part of his argument for GMR was incompatible with another part of his philosophy. By recognising this point as an ad hominem, the author is carefully noting its limits; it doesn’t show that GMR itself must have such an incompatibility, rather that Lewis’ own view is problematic.

    So what does ‘ad hominem’ mean? Literally ‘to the person’, and taking it this way makes sense in light of the previous example. The inconsistency is a problem for Lewis and anyone else who might hold the relevant positions. Jack’s use of ‘idiot’ is quite clearly a personal remark towards Jill and so it is also ‘to the person’, albeit in a different way to that in the GMR paper. It seems strange then that Jack would deny this. However, Jack reasoning is surely that he takes ‘ad hominem‘ to be short for ‘argumentum ad hominem’, i.e. an argument to the person. “You only think that because you’re an idiot” is not an argument at all (unless we take it that an argument is implied by the statement), and so it doesn’t seem to qualify as an argumentum ad anythingWhat we’ve seen from my GMR example though is that philosophers sometimes use the term ‘ad hominem’ with regard to sentences that aren’t arguments. All that’s necessary is that the statement, the point, the argument, whatever must be aimed towards the arguer in some way. Surely then Jill is correct to call Jack’s retort ‘ad hominem’, since his point was aimed at her rather than at her arguments or her position.


    Ad hominem as a fallacy

    Jack might make another objection to the idea that he was engaging in ad hominem: “Yes, my calling Jill an idiot is ‘to the person’, but ‘ad hominem‘ is a fallacy, and nothing I said was fallacious. I didn’t claim that  the fact that she only thinks that blue is best is because she’s an idiot is an argument for why ‘blue is the best colour’ is false. All I said was that her idiocy makes her think that. It’s a genetic point but not a genetic fallacy.”

    Is Jack right? I don’t think so. The GMR example shows an instance of a philosopher engaging in ad hominem in a way that isn’t fallacious – the acknowledged ad hominem nature of the point made against Lewis means that it is limited, but included as it is still interesting and relevant.

    Another use of ‘ad hominem’  is found in J.L. Mackie:2

    [Berkeley] has an argumentum ad hominem against Locke and his followers: they concede that nothing resembling our ideas of secondary qualities, such as colours and sounds and heat and cold and so on as we perceive them, can exist independently; but they give no reason for supposing that it is otherwise with the primary qualities like shape and size and motion…


    Mackie’s use of the term here is very broad, and in the above example it denotes the fact that Berkeley is arguing against the set of arguments provided by the Lockeans. So why call it ad hominem? Mackie’s purpose is surely to make it clear that Berkeley’s objection to Locke does not rule out the possibility that somebody might be able to provide a reason to think that primary qualities can exist in extended space. Nevertheless, Berkeley’s ad hominem has some force – Locke did not succeed in doing it and so somebody would need to do so in order to rescue the Lockean philosophy. This instance of an argumentum ad hominem then doesn’t seem to be fallacious.

    So what sorts of ad hominem argumentation would be fallacious? Of course, this will depend on what we are willing to call a ‘fallacy’. Some might limit the term to ‘errors in explicit informal reasoning’, such as in the example Jack provided when rebuking Jill, i.e. “it’s false that blue is the best colour because you’re an idiot”. That would surely count. What about Jack’s first reply to Jill, i.e.  “You only think that because you’re an idiot.”? Jack is right to say that he is not claiming that it disproves Jill’s proposition, but surely then whether or not Jill’s thinking blue is the best colour is because she’s an idiot is irrelevant to the argument. Its irrelevance is enough to make it fallacious. Is irrelevance enough to make a point fallacious? It seems to me that if we are willing to consider red herrings and ignoratio elenchi to be fallacious, there seems to be no reason to make a special case of an ad hominem irrelevance.

    With that in mind, I’d say that Jill is right, adding in that Jack’s reply was fallacious. By immediately speculating about Jill’s reasons for believing that blue is the best colour and worrying about whether or not she is an idiot, Jack is engaging in an ad hominem objection, and the fallacy results from its irrelevance.



    1 I’d cite it, but unfortunately I can’t remember which one it was. I have a big wadge of papers about modality that I can’t be bothered to read through (especially as they’re printed and I can’t Ctrl-F). If I manage to find it I’ll update the post. Until then you’ll just have to take my word for it!

    2 The Miracle of Theism: Arguments for and Against the Existence of God (1982), Oxford University Press (pp. 69)

    Category: PhilosophyReason and Argument

    Article by: Notung

    I started as a music student, studying at university and music college, and playing trombone for various orchestras. While at music college, I became interested in philosophy, and eventually went on to complete an MA in Philosophy in 2012. An atheist for as long as I could think for myself, a skeptic, and a political lefty, my main philosophical interests include epistemology, ethics, logic and the philosophy of religion. The purpose of Notung (named after the name of the sword in Wagner’s Der Ring des Nibelungen) is to concentrate on these issues, examining them as critically as possible.

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    • My critique of the utility of AAH (and the laundry-list o’ fallacies in general) is that they are binary, and demark only absolutes. The real world is messy and the best grist for our argumentation mills are probabilistic relations, not absolute ones.

      If it’s true that Jill is an idiot, does it prove that her claim is wrong? No, of course not. Does it change the likelihood of it being correct? Quite possibly. Having impaired intellectual functioning actually is related to the determining of difficult conclusions.

      Or to cite a real world example, in a court of law a witness’ testimony can be discounted if it is shown that they have a history of lying or mental instability. Do those facts prove a person’s testimony is incorrect? Not at all. Do they change the likelihood? Yes, and we weight it accordingly (or, we’d be wise to).

      The fallacies themselves are often irrelevant for these reasons, without the wielders of them knowing it.

    • An Ardent Skeptic

      There’s a reason why I just say that someone has engaged in a personal attack. Jack’s crack is a personal attack whether it’s an ad hominem or argumentum ad hominem or neither. Easier just to call a spade a spade.

      Good post, Notung!

    • padawanphysicist

      Great analysis.

    • This, exactly.

      There’s only a problem with an ad-hominem attack if you’re using it as a replacement for all other arguments. It can certainly be valid as one component.

    • bluharmony

      I’m just repeating what I said about this on my FB page: Haha… I tried a similar argument on FTB & was instantly called an idiot. I’d like to note that ad hominem attacks are not necessarily the same as informal logical fallacies, and some dictionaries actually make this distinction. Moreover, there’s no need for either if your rebuttal to the original argument is sound.

    • bluharmony

      This is so true, although the actual rule of law is this: Evidence of a person’s character or character traits is not admissible to
      prove that on a particular occasion the person acted in accordance with
      the character or trait. (There are then various exceptions to the rule.) As for witness testimony, it’s up to the finder of fact (judge or jury) to decide if they’re credible. Competency is a different issue.

    • Pete

      But most people who throw around the term “ad hominem” on the internet intend it as a shorthand for “argumentum ad hominem.” So, while Jill might be technically correct, it could be a case of two wrongs making a right.

    • Prepagan

      The sceptic community seems awash with those willing to throw around such shorthand references to perceived fallacies, often leading to off topic, time wasting arguments over definitions.

      As in the example in the main post – Jill’s attempt to get Jack to address her point has been deflected by an enthusiasm for debating the applicability of a Latin label and any hope of useful discussion on the main point has been lost.

      It would be nice to think that this attempt to set the record straight will help keep discussions on track but I can’t help thinking that the reverse is more likely and that we now have a freshly enthused batch of debaters looking for an opportunity to pounce on any clumsy use of the ‘ad hominem’ tag. Sigh.

    • When people use ad hominems and then say ‘it was offered as an insult, not as an argument’, I always reply ‘interesting how you changed the subject.’

    • True, but I’d say personal attacks were a subset of ad hominems, that is to say that ad hominems can be used in good spirits!

    • I agree, but I suppose the philosopher would want to show where the argument itself goes wrong, since that’s their purpose. With a witness’ testimony all you are trying to show is that the testimony is a reliable (or unreliable) one.

      However, in our ordinary lives we make ad hominem judgements all the time. How do I know that quantum mechanics is a robust scientific theory? By appeal to authority only (at least in my case). Does this prove quantum theory? No – but it makes it probable that the evidence for quantum theory is strong, exactly in the way you are talking about.

    • That’s it – and not all ad hominems are attacks!

    • I’ll have to try that one!

    • True, but those who use ‘ad hominem’ as a shorthand for argumentum ad hominem should be more tolerant of those who define it more broadly (and as I’ve tried to show, using it in this broad way is a common practise among philosophers – there are more examples than the two I provided).

    • bluharmony

      Right, it’s just a comment that goes “to the man,” like “privilege,” for example. You can’t rebut an argument by accusing someone of privilege because that’s a classic ad hom (and poor reasoning, since “oppression” doesn’t necessarily make an argument logically sound).

    • I suppose my purpose was what you are talking about – lots of people claim that ad hominem has been used incorrectly when in fact it hasn’t. I get your point though and feel the same way – I’d much rather someone shows how a particular argument fails rather than simply waving their hand and saying ‘non sequitur!’ or whatever.

      Schopenhauer wrote (from the top of my head) with irony something along the lines of “if you want to win an argument, describe your opponent’s argument such that it has already been refuted many times in the past”. I think people often do that with the ‘list of fallacies’.

      I’ll try to find the exact Schopenhauer quote soon. This time I know which book it’s from!

    • I agree – the ‘privilege’ stuff is classic ad hominem, and fallacious too, at the very least because of its irrelevance.

    • I agree. Mostly I am not commenting on what philosophers do, but on what non-philosophers do with a philosopher’s tools. That is, I am saying tools are irrelevant when wielded by novices. The popular belief in the community is to the contrary (imo). Many self-described skeptics fail to understand the limitations and proper use of AAH and other informal logical fallacies.

    • No, there’s a problem with any attack, period.

    • An Ardent Skeptic

      That is very true, Notung, but also very rare! Humans are far quicker to find fault and state their objections in destructive ways. That’s why great blogposts that people largely agree with pass without comment, while the controversial ones rain down a torrent of negativity.

    • jackill

      “Blue is the best colour”
      Jill didn’t said ” for photosynthesis” or anything else, but he speaked in an absolute manner.
      In actual state of science, this sentence is nonsense, so we can reasonably think that Jill is an idiot.
      Jack said ” BECAUSE you’re an idiot”.
      It seems that Jack believes to another color, or that Jack thinks there can be a causal relation between ” being idiot ” and ” blue is best” . In that case, Jack would be an idiot too.

      But it can be false.
      Perhaps Jack thinks that only an idiot can have such a reasonment about colors.
      In that case, it would be simply a logical deduction, not insult neither ad hominem.

    • Prepagan

      This sounds a little like the twenty-fourth of Schopenhauer’s stratagems taken from his essay ‘The Art of Controversy’ translated into English in 1896 and later re-titled ‘The Art of Being Right’.

      Although I’m a little concerned that prompting people to look this up may do more harm than good in the context of this post 🙂

    • If Jack’s initial retort isn’t a classic ad hominem circumstantial I’ll eat my hat.

      That said, I tend to agree with the point made earlier that it’s much more important to explain why an argument works or doesn’t than to affix a Latin label. If Jack really thinks that his initial response won’t be taken as an attempt at prebuttal of Jill’s forthcoming Argument for Blue, well, he’s an idiot.

    • Ad hominem is a tricky subject. Strictly speaking, it is a logical fallacy. In an ideal sense, an argument stands or fails on its own, no matter where or whom it comes from, even if everything that source has said up to this point has been a bad argument or an outright lie. That said, “considering the source” is a useful shorthand, and in the real world, one needs to take prior veracity and source bias very much into account. Especially given the complexity of an argument in a given report or scientific paper, which may require a great deal of analysis to evaluate for errors of fact, methodology, or logic.

      This kind of “ad hom” is even enshrined in law, as evaluation of the veracity of sources is a standard part of legal procedure in a court of law.

      Hence, my default when somebody from the Discovery Institute is presenting even a very sophisticated argument ostensibly discrediting biological evolution is to not believe them, and I’d demand a very high burden of proof from these people, given the prior track record of “creation science” and “intelligent design”.

    • Yes, instead we should allow the continued spread of bullshit which is dangerous to all of humanity, like anti-vax. We shouldn’t attack them at all. We should instead appeal to the rationality of the .01% of the population which can do nothing whatsoever about the problem, but will listen to the facts.

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