You Would Say That

Clare Moriarty on philosophical mud-slinging and ad hominem arguments

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Search social media for the term ‘ad hominem’ and you will be met with a slew of posts lamenting or lambasting an opponent’s use of this lowest rhetorical trick. Such commentary is often accompanied by suggestions that their interlocutor look up the term’s meaning, or, in more generous cases, profferings of definitions equating it with a personal attack. As many tweets advise, ‘ad hominem’ describes an argument directed at a person, and the term is conventionally thought to carve a line between this personal way of arguing, and arguing ‘ad rem’ or ‘at the matter or thing’, where the matter or thing in question is the content or quality of your opponent’s argument. So, ‘ad hominem’ marks out a distinction between responding to the arguer and responding to their argument. And, in popular discourse, it has become a loose synonym for any kind of bad argument that tends toward the realm of the personal. What may come as a surprise, then, is that the practice of ad hominem argument has a relatively respectable legacy.¹

The Latin phrasing ‘argumentum ad hominem’ reaches back at least as far as the late sixteenth century and is discussed in more general terms in sources as remote as Aristotle. Within philosophy, ad hominem argument finds a happy heyday in the eighteenth century, when a boom in this kind of argument was representative of a feeling that a philosopher should be able to live in accordance with their declared principles, and that performative contradiction between life and theory reflected on a theory’s tenability. In an introduction to eighteenth-century philosophy, Knud Haakonssen explains that there simply was no austere separation between theory and practice in the way that is sometimes imagined: ‘The pervasive use of the ad hominem argument is significant. Wave after wave of undesirables—epicureans, deists, sceptics—was supposedly stemmed by the argument that they could not "live" their philosophy.’

To take a pair of related and somewhat morbid examples, consider the following reactions to the deaths of David Hume and André-François Boureau-Deslandes, both of which focused on a purported obligation to live (and die) in accordance with one’s philosophy.

‘Father of economics’ Adam Smith penned the obituary for his friend, ‘father of naturalism’ David Hume. Given the somewhat scandalous reputation Hume had for atheism (or, at least, for powerfully unorthodox religious views), this was a delicate business. One thing the fervid theist might be watching for—in the case of a heretic approaching death—is any shiftiness around expiry, perhaps revealing a fear in the atheist that they had got it wrong. Loyal to the end and mindful of Hume’s reputation, Smith made clear that far from trembling before the wrath of God, Hume was cheerful to the end. He wrote:

[Hume’s] symptoms, however, soon re turned with their usual violence, and from that moment he gave up all thoughts of recovery, but submitted with the utmost cheerfulness, and the most perfect complacency and resignation.

Upon his return to Edinburgh, though he found himself much weaker, yet his cheerfulness never abated […]

His cheerfulness was so great […] that, notwithstanding all bad symptoms, many people could not believe he was dying.

‘Doctor,’ said [Hume], ‘as I believe you would not chuse to tell any thing but the truth, you had better tell him, that I am dying as fast as my enemies, if I have any, could wish, and as easily and cheerfully as my best friends could desire.’

A natural response at this point might be to assume that such precaution is overkill and that it would be preposterous to demand that a person smile at death, whatever their metaphysical assertions in that direction. After all, there’s more to worry about in mortal illness than hell alone, and surely nobody was looking to leverage anxiety about sickness and death against those who held reformist views. And yet, that was exactly what Hume’s canonical predecessor George Berkeley had done a few years earlier.

Though Berkeley and Hume shared views on philosophical methodology, they could hardly have been further apart on religion, and much of Berkeley’s writing career can be understood as a war against a group known as the ‘freethinkers’, composed of a mixture of deists, libertines, and anyone pursuing religious reform along more naturalistic or liberal lines. When, as a young man, Berkeley was writing pithy invective against these same freethinkers in the magazine The Guardian (1713) he made exactly the kind of inference Smith feared about philosophe André-François Boureau-Deslandes. A year earlier, Boureau-Deslandes had published A Philological Essay, or Reflexions on the death of Free-thinkers, with the characters of the most eminent persons of both sexes, ancient and modern, that died pleasantly and unconcerned, &c, chronicling some secular perspectives of past thinkers on death as a kind of grist to the freethinker’s mill. This outraged Bishop Berkley, and he saw opportunity in Boureau-Deslandes’s subsequent illness to mock what he took to be the freethinker’s failure to live up to the letter of his purported ‘happy death’ principles, writing: ‘this gentleman’s appearing very sorry that he was not well during a late fit of sickness, contrary to his own doctrine, which obliged him to be merry upon that occasion’.

The philosopher John Locke also ruminated on reasonable argument at some length in his Essay Concerning Human Understanding. He makes a clear contrast between arguing against a position in the traditional philosophical way (criticizing a premise or an inference), and trying to persuade against the same position by appealing to features external to the pure content of the argument. Locke categorizes these argument into four types, only one of which ‘advances us in knowledge and judgement’ and ‘brings true instruction’. All other kinds of argument, including ad hominem, are used to support something already argued or to silence a certain kind of objection. An ad hominem argument is at best a secondary argument.

Locke presents ad hominem as a device either to bolster support in an established claim, or to block an argument by pointing to features of the argument’s context, involving the beliefs, behaviours, or principles of the opponent—ideally, features in tension with the content of the argument. We might imagine sitting at dinner with someone who berates us for our moral failings in not observing a vegetarian diet. The arrival of their plate, if it contains a piece of venison, should give us pause and impact our engagement with their argument, at least in the sense of listening to their arguments in good faith. Locke’s interpretation involves appealing to ideas already accepted by an arguer, and demonstrating that their behaviour concedes commitments of various kinds.

For these reasons, people have argued that it’s a mistake to think of the ad hominem argument as fallacious. After all, common sense suggests that some ad hominem arguments are better than others, and the best of the better ones are persuasive. They tell you that, given an understanding of the public sphere as a kind of marketplace of ideas, some vendors should be treated with more suspicion than others because they tell us we must do or believe one thing while they do or believe another. This casts doubt on their prescriptions and suggests that we should be cautious in accepting their argumentative premises. Thus, the defence of ad hominem arguments relies on the relevance of speaker’s behaviour to an argument’s premises.

One noteworthy ad hominem commentator was Finnish logician Jaakko Hintikka, whose shrewd analysis of the argument amounted to thinking about it as an argument that ‘works’ relative to a particular user (Aristotle discussed something similar). Conventional wisdom claims that an ad hominem argument is an instance of the relevance fallacy: it drags irrelevant material into a place it doesn’t belong. Hintikka’s point is to show that this material may well be relevant in specific contexts. Indeed, ad hominem considerations can be made logically respectable with the addition of novel premises about the argument’s creditability in light of the inconsistency of the arguer. It isn’t a matter of logical fallacy, but rather a recognition that the argument has a special limitation—it won’t work universally.

We might concede that there are certain domains in which ad hominem argument is more natural and appropriate than others. Maybe it is only in moral and ethical domains that ad hominem arguments highlight the tenability (or otherwise) of theories? Certainly, we may have every reason to take a person’s testimony much less seriously if it turns out that the kind of rule they prescribe as applicable to everyone is one that they flout in their own decision-making. Perhaps unexpectedly, however, the history of mathematics suggests a wider role for ad hominem arguments.

Mathematical history has witnessed many sordid disputes, and the conduct found in the priority debate over whether Newton or Leibniz deserves credit for the invention of calculus would surprise anyone with a sense that mathematics concerns only civilized computation and collaboration. These episodes tended to be very much about morality and who stole what from whom—but surely one doesn’t argue ad hominem in debates about mathematical truth? In fact, that’s exactly what we see in some of these disputes.

At the beginning of the twentieth century, Ernst Zermelo, one of the founding fathers of set theory, was trying to settle on fundamental axioms for a paradox-free mathematical theory. Key opponents of Zermelo’s work, known as the ‘French analysts’, maintained a more trepidatious attitude towards many assumptions in early set theory. Baire, Borel, and Lebesgue argued that you needed to be able to positively demonstrate the truth of any mathematical statement for it to be believed to be true, and this wasn’t possible for Zermelo’s programme, and particularly his ‘axiom of choice’. Their correspondences show deep philosophical disagreements on mathematical knowledge and are a reminder that what seems mathematically self-evident is often anything but, and indeed is quite opaque—echoes here of philosophy and mathematics Twitter erupting over the truth of ‘2 + 2 = 4’.

Zermelo used his opponents’ own mathematical conduct to show them that they were more sympathetic to his position than they realized. He pointed to instances where pieces of ‘settled’ mathematics assumed some equivalent of his axiom (for example, in the work of giants such as Cantor and Dedekind, and even in their own research), and to instances where principles with a similarly problematic self-referential or ‘impredicative‘ component were used in well-known pieces of mathematics, seemingly without objection. In this way, Zermelo suggested to his opponents that though they preached a rigid mathematical manifesto, they could not live it. They too flouted its principles in their own proofs and frequently failed to object to violations elsewhere. Such conduct showed them to be mathematically conservative in theory, but not in practice. And, perhaps, such concessions suggested something even stronger, such as the indispensability of the axiom for regular mathematical practice.

Importantly, Zermelo wasn’t really interested in anything like a character flaw in his opponents. What did interest him was what their ideological infidelities told us about their position—that rigid constructivism is harder to uphold than they acknowledged. When constructivists were in the business of trying to produce mathematical results, rather than philosophically theorizing about what they took their work to be committed to, they were as liable to proceed in the same way as Zermelo. Even if Zermelo’s opponents owned their concessions and could re-write the relevant mathematics without appeals to the problematic material, the ad hominem served an important purpose. Even adamant antagonists of a view may not be so wholly dedicated that they don’t misstep when they are not watching what they are doing.

Such cases show us something important about certain kinds of ideology and its fate when tested against ordinary practice. In this way the ad hominem serves its purpose. Argumentum ad hominem is not necessarily about slinging mud, but is often about philosophical and ideological practice, and what it is practical to expect from people who make arguments in the public sphere. #notalladhominems

Notes

¹ Hereafter, I will maintain the roman ‘ad hominem’ since the term appears so frequently that I’d rather avoid the sense of the text staggering towards falling over that so much intermittent italics might produce.

Clare Moriarty

Clare Moriarty is IRC Postdoctoral Research Fellow at Trinity College Dublin and a Fellow of the Forum for Philosophy. Her work focuses on the history and philosophy of maths, especially in the early modern period, and in particular the evolution of calculus.