Ad Hominem Arguments and Ad Hominem Fallacies

Just as not all slippery-slope arguments are slippery-slope fallacies (see the post of 19 November 2003 in the AnalPhilosopher archive), not all ad hominem arguments are ad hominem fallacies. If you want to learn the difference between the ad hominem argument (i.e., the argumentum ad hominem, or argument to the person) and the ad hominem fallacy (attack on the person), read my essay “How to Argue,” a permanent link to which appears on the left side of this blog.

Here’s the difference in a nutshell. The ad hominem fallacy consists in dismissing a person’s argument on the basis of some negative characteristic of the person (rather than because of some defect in the argument). That you are a jerk does not make your arguments bad (any more than your being a saint makes your arguments good).

Note that this fallacy requires dismissal of an argument. It has the form:

1. S is a bad person (in some respect).

Therefore,

2. S is a bad arguer (i.e., S's argument is bad).

Compare:

1. M is a small animal.

Therefore,

2. M is a small mouse.

That this is invalid is easily seen, for the premise can be true while the conclusion is false (if M is a large mouse). The invalidity consists in transferring a relative term (“bad” or “small”) from one class to another. That this cannot be done is clear; the criteria for smallness in animals differ from (or rather, are not necessarily the same as) the criteria for smallness in mice. The criteria for badness in persons are not necessarily the same as the criteria for badness in arguers. Good people can be bad (or merely nongood) arguers. Bad people can be good (or merely nonbad) arguers. (For further discussion, see my textbook Informal Logic, 3d ed.)

One does not commit the ad hominem fallacy merely by attacking or disparaging a person. That may be disrespectful, but disrespectfulness is not a fallacy. It’s a vice, a character defect. A fallacy is a psychologically attractive but logically defective argument. It is a mistake in reasoning, not a way of treating someone.

The ad hominem argument, which is perfectly legitimate, indeed essential to effective persuasion, consists in holding people to their beliefs, values, or principles. If you’re a Christian and I point out to you that you’re not living up to your Christian principles, I commit no fallacy. I’m simply helping you be a better Christian, for which you should be grateful, not resentful. I do not need to be a Christian myself for this to work.

All of which is to say that I did not commit an ad hominem fallacy in my post (see here) about Michael Moore. I couldn’t have, since I didn’t dismiss any argument he made. (Does he make arguments?) Perhaps I was disrespectful to Moore, in which case I was bad. Then again, perhaps he doesn’t deserve respect, in which case I wasn’t bad. Respect must be earned.