You know what’s tiresome? Arguing on the internet. “Three-eight-sixing“, as it’s known. Few of us can resist it – God knows I find myself rolling up my sleeves and plunging elbow-deep into the stuff below the line often enough, and a few minutes ago I broke my own rule of not getting involved in Twitter arguments. (I tweeted something involving the words “Richard Dawkins” and “abortion”. I had it coming.)
But assuming you’re going to argue on the internet (which you are), then you know what’s even more tiresome? “Logical fallacies” thrown around by people who have only the faintest understanding of what they mean.
You will have experienced it. “Person X is stupid and/or annoying”, you say; immediately you are told “AD HOMINEM! Play the ball, not the man!” “I don’t know much about Y, but this professor of Y-ology seems to think it’s…”, you begin, only to hear “BZZZZT! ARGUMENT FROM AUTHORITY!” Or (relatively recent development this) “There are similarities between Z and the situation in 1930s Germany” – “ARGUMENT AD HITLERUM! GODWIN’S LAW!”
Now, it has been years since I did philosophy and I don’t claim to be an expert. And fallacious arguments are indeed worth being aware of and avoiding. There’s a very useful list of them on Wikipedia and a rather smug downloadable poster of them here.
But the fact that someone, say, insults the person they are arguing with, or recruits an authority to support their argument, or suggests that taking action P now could lead to undesirable outcome Q in the future (“SLIPPERY SLOPE FALLACY!”), does not mean that they are committing a logical fallacy and should therefore be ignored.
“Argumentum ad hominem” is probably the most widely misused. Most people know, now, that if someone insults you while criticising your argument (“You’re a stupid-head! And your claim that government spending has a fiscal multiplier of 1.19 fails to take into account all the externalities”), they are not committing an ad hominem fallacy, they’re just insulting you. “Argumentum ad hominem” means suggesting that we should ignore or distrust someone’s arguments not on the strength of the evidence but because of who they are.
But even that is not always a fallacy. It can be perfectly logical to discount someone’s argument because of who they are: if a car salesman has previously sold me a dud car, then it makes sense to ignore his argument, supported by evidence from the milometer, that the Vauxhall Astra he’s trying to sell me now has only done 10,000 miles. In order to show that someone is using the ad hominem argument fallaciously, you need to show that they have no reason to distrust their opponent, or to show that the argument is valid regardless of who they are.
Similarly, it is only fallacious to appeal to authority if the authority is not trustworthy. An appeal to authority can’t logically prove something to be true – it’s an inductive, not deductive, argument – but it can provide you with a good reason to believe something. I can’t be an expert on every subject, so I have to outsource my expertise to others: I don’t know how best to keep my bike running smoothly, but the guy at the shop says I should make sure I change gears on my front chain-ring regularly, and most other bike experts would agree with him. If someone claims that their appeal to authority proves beyond all doubt that their claim is true, or if they have appealed to an untrustworthy authority or one which does not represent the views of most other authorities on the subject, then you may be able to accuse them of a fallacy. But again, you need to show it, not just say it.
No doubt people will argue with my claims above, and that’s fine – as I said, I don’t claim to be an expert, so please do point out any mistakes I’ve made. But the point is that, sometimes, arguments of these forms, and of other so-called fallacious forms, are perfectly valid ways of supporting a point, and to claim otherwise you need to do arguing of your own, not use shortcuts. Shouting “Fallacy! Don’t need to listen to you any more” is itself fallacious. We could call it the false fallacy fallacy.