• 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.