You’re using ad hominem wrong, and it’s making you look silly.

(Maybe).

Ad hominem is an informal logical fallacy. It means “at the person” – implying that the attack is on the person and not their argument, but, crucially, it presents itself as an attack on the argument. Let’s have a look at what ad hominem is, and, just as importantly, what it isn’t.

We’re having an argument. You assert \(Y\). However, I’ve known you for a pretty long time, so I know what a total wanker you are, and therefore that everything you say is wrong.

\(X\) – Your argument.

\(W\) – You are a wanker.

\(W \implies \neg X.\)

(W implies not X).

Because you’re a wanker, what you’re saying is wrong. This is ad hominem. It’s a fallacy because, you may well be a wanker, but it has no bearing on whether what you’re saying is true – unless, of course, you’re saying you’re not a wanker, in which case the fact of you being a wanker is actually pretty pertinent. This form of argument is flawed, where it’s argued that some statement \(X\) unrelated to the person making it is wrong because of some unrelated fact \(W\) about them, and I hereby encourage you to call it out.

So what isn’t ad hominem?

Well, what if, instead, I assert that you’re a wanker because you think \(X\):

\(\text{Believing } X \implies W\).

Now, this does presumably rest on the assumption \(\neg X\). But it’s not ad hominem, because it isn’t an argument against \(X\). There are also some pretty obvious examples where this is true: if \(X\) is, “III is the best Godfather film”, then I think it’s pretty incontrovertible that you are, in fact, a wanker¹.

We’re having an argument. Things get a bit heated, and, in a moment of passion, I… well… look, I called you a wanker, ok? I’m sorry. It was rude and inappropriate, and I let my emotions get the better of me. But that doesn’t mean my argument was ad hominem. It doesn’t even mean that I was wrong – in fact, stating that I’m wrong because I got emotional is ad hominem. What I said comprised two separate statements:

\(\neg X, W\).

In this case and the last, \(W\) is just name-calling. Name-calling isn’t a form of argument. It has no bearing on the arguments of the people who call people wankers, or of the wankers themselves. Now, it’s a separate question whether name-calling is acceptable or not, but I’m averse to being puritanical about it, partly because that leads to exactly the kind of derailment that we claim to be attacking when we roll out $10 words like ad hominem. If you’re serious about rigourous debate, treat name-calling for what it is: besides the point. Don’t capitalise on it as the QED for your argument. And don’t call something ad hominem when it’s not.