Jill: The minimum wage should be higher. It is important that employees be able to make a living wage, and economic studies indicate that raising the minimum wage will probably not significantly reduce employment.This is a really blatant ad hominem; Frank is ignoring Jill's argument, and instead saying something about Jill herself—in this case, something completely irrelevant. But one can have ad hominems without this kind of irrelevance, as in this version of the case:
Frank: Jill often keeps her library books past the due date. Don't listen to her, the minimum wage is fine as it is.
Jill: The minimum wage should be higher. It is important that employees be able to make a living wage, and economic studies indicate that raising the minimum wage will probably not significantly reduce employment.This version is less off-the-wall—one can actually imagine Frank arguing in this way—but it's also pretty clearly an ad hominem. Frank has ignored the argument Jill made, and is instead focusing on Jill herself.
Frank: Jill works a minimum-wage job, so her motives aren't pure. The minimum wage is fine as it is.
Argumentum ad hominem is typically recognized as an argumentative fallacy. Perhaps sometimes it's appropriate to argue about the person—perhaps, for example, in some electoral cases, one of the main questions we're interested in is what kind of a person is this?. But establishing something bad about a person making an argument is not to be confused with arguing against the conclusion. So much is, I think, pretty much obvious, once it's spelled out. But there are at least two kinds of cases where ad hominem arguments can be misleadingly tempting.
Consider arguments involving hypocrisy. Someone is hypocritical when one condemns behaviour of which one is oneself guilty. When Newt Gingrich got all high-and-mighty about Bill Clinton's marital infidelity while at the very same time carrying on with a secret affair, that was hypocrisy. When people are guilty of hypocrisy, it can feel pretty satisfying to call them out for it—it's a strong rhetorical move. But it's also argumentum ad hominem. It says something about the person making the argument, rather than about the argument or conclusion itself.
Jill: The minimum wage should be higher. It is important that employees be able to make a living wage, and economic studies indicate that raising the minimum wage will probably not significantly reduce employment.Frank may succeed in getting people not to listen to Jill with this argument, but he does so in a way that totally ignores the content of what she actually said. Her argument is about what employees need and the relationship between minimum wages and unemployment. Frank has totally ignored that argument, and focused on Jill instead. That's the definition of ad hominem. If you don't care about Jill and only want to know what to think about the minimum wage, Frank's argument is just a distraction. Accusing people of hypocrisy is ad hominem.
Frank: Jill doesn't really care about people making a living wage—her company profits tremendously from underpaying its employees.
The same goes, I think, for at least some self-defeat arguments. In my introductory epistemology course this week, we're discussing radical skepticism—the view that nobody knows or has any reason to believe pretty much anything. (Think about all the possible ways any of your beliefs could be wrong—you could even be a brain in a vat!) One charge people often level against this view is that it is self-defeating in the following sense: no skeptic can coherently claim to know, or have reason to believe, that skepticism is true. One imagines winning an argument with a skeptic, perhaps along lines like these:
Jill: Nobody knows anything. After all, it's possible to be deceived about any possible belief.Frank's argument is clever, and he might even convince people not to listen to Jill. But his argument is ad hominem. He says that Jill is being inconsistent in a certain kind of way, not that the content of her view is. Jill has given an argument having to do with the possibility of error—the argument does not depend on there being any individual who can coherently endorse it. Frank has ignored Jill's argument, and attacked Jill herself. That's the definition of an ad hominem argument.
Frank: Jill can't possibly know what she's talking about, because if she did, then that would be some knowledge someone has.
One difference between this last kind of ad hominem and more prototypical cases is that it doesn't depend on particular contingencies of Jill's—there's a kind of argument template that one could use against any skeptic. But that's just to say that one is prepared to give an ad hominem argument against anyone who thinks radical skepticism is true. But this isn't an argument against radical skepticism itself.
Here is a coherent hypothesis: nobody knows anything. Arguing that nobody could know it is a very different thing from arguing that it's false. The self-defeat argument only does the former; it is ad hominem.