The ad hominem argument is where you seek to discredit someone’s argument by drawing attention to their motive, character, authority, education, age, state of mind, etc., rather than showing what is wrong with the argument itself. It is one of the most common logical fallacies and ways to derail an argument.
For example, if a senator argues for a pay raise you might say:
Of course he would say that. He’s a senator.
It is a logical fallacy, a fault in reasoning, because it fails to point out what is wrong with the senator’s argument. Arguments stand or fall on their own merits, not on who made them and why.
That applies even to arguments made by authorities and experts. Good ideas often come from outsiders. If the argument is wrong there will be a mistake in it somewhere – no matter who made it.
It is also a good way to derail an argument because most people will feel the need to defend themselves. The argument becomes personal.
Unlike slander it can be based on the truth: a person might in fact be a senator – or a high school dropout or work for an oil company or be dating a white woman or whatever will make others doubt him.
Unlike name calling its aim is not so much to hurt someone’s feelings but to discredit what they are saying. Of course you can do both at the same time.
On this blog the ad hominems often concern race.
For example, when a commenter says that blacks have less intelligence than whites, his race is sometimes brought into it. If he is white, he is dismissed as a racist. If he is black, he is dismissed as self-hating.
It is an ad hominem because it seeks to dismiss his argument based on his personal qualities, not on what is wrong with his argument. If there is a mistake it will be in the argument itself – like bad reasoning or bad facts – not in the colour of his skin. Or how you hate his website. Or what books he has not read. Or what trouble he is having with his wife.
Education, knowledge, experience and intelligence do tend to make one’s arguments better, but it does not necessarily make them true. If only it were that simple. Also, one can lack all those things and still be right – or see what someone with a PhD is overlooking.
A reverse ad hominem is where you point out the arguer’s personal qualities to defend rather than discredit his argument. Appeal to authority is the most common kind. Tim Wise has built his life’s work on the reverse ad hominem of his skin colour.
While this tends not to derail an argument and, given human nature, is often necessary to persuade people, it proves nothing in and of itself. After all, authorities can be wrong. Tim Wise can be wrong. Even fair-minded people with no personal reason to favour one side can be wrong.