Ethics Explainer: Ad Hominem Fallacy

Ad hominem, Latin for “to the man”, is when an argument is rebutted by attacking the person making it rather than the argument itself. It is another informal logical fallacy.

The logical structure of an ad hominem is as follows:

1. Person A makes a claim X.
2. Person B attacks person A.
3. Therefore, X is wrong.

When you see the logical structure of the argument it becomes clear why it’s a fallacy. The truth or falsehood of X has nothing to do with the person arguing in support of it. Imagine if X had been written down and you didn’t know who was arguing the case. If you couldn’t prove it wrong with arguments, then you can’t prove it wrong at all.

Here are some common ad hominem arguments:

Argument from abuse

Steve: “I don’t think we should catch a taxi to dinner. It’s just a short walk and the environment doesn’t need the extra pollution.”

Jaime: “You would say that – you’re so cheap!”

Jaime’s rebuttal doesn’t address Steve’s argument. Instead it abuses him as a person. Not only is this unpleasant, it’s fallacious because Steve’s character doesn’t impact on the truth or falsehood of what he said.

‘Tu quoque’ fallacy

Jaime: “Now that online streaming services are affordable and available in Australia, there’s no justification for pirating films anymore. People shouldn’t do it.”

Steve: “But earlier you’d said you were about to download a torrent for the new Game of Thrones!”

‘Tu quoque’ is Latin for “you also”. The ‘tu quoque’ fallacy occurs when an argument is rebutted because the arguer’s own behaviour is contrary to what they’re arguing. While this is a good way of highlighting hypocrisy, it isn’t a refutation. Just because a person doesn’t ‘walk the walk’ doesn’t mean what they say is false.

Appeal to authority

Steve: I don’t believe in God. Richard Dawkins is an atheist and he’s really smart.

The appeal to authority is actually a reverse ad hominem in which the credentials of another person are used to strengthen an argument. Rather than relying on arguments against God’s existence, Steve relies on the authority of other people who don’t believe in God.

Although it isn’t criticising the person making the argument, it still doesn’t deal with the argument itself. The appeal to authority is another kind of ad hominem fallacy.

Note that the ad hominem fallacy only applies to attempts to discredit (or strengthen) an argument by reference to the person making the argument. In court cases, lawyers will often use a person’s character to prove or undermine their credibility.

This is not necessarily a case of ad hominem – credibility is about whether or not we should believe whether a person is telling the truth, not whether the arguments they make are reasonable ones or not.