Thursday, August 12, 2004

The "Ab Homine" Fallacy

We've all heard of the "ad hominem" ("to the person") fallacy, which involves insulting the person who made an argument rather than refuting the argument itself. (This should be familiar to anyone who has followed the debates over Kerry's Vietnam service.)

For all I know, the fallacy I'm about to discuss already has a name somewhere, but I'd like to call it the "ab homine" fallacy. If I'm correct in dusting off my old Latin skills, that means "from the person." The fallacy consists in saying, in effect, "My argument is particularly valid because I used to belong to the other side."

How is this different from the argument to authority? Because the person making the argument doesn't claim any expertise or authority. Rather, he or she claims to be credible based on his or her own decision-making process and history.

Examples abound. You can hardly read anything about politics without running into the person who says, "As a lifelong Republican, I can't vote for Bush," or, "As a former environmentalist, I see the irrational nature of that movement's demands," or the like. (See this New York Times article, or this recent op-ed, for example.)

Why is this a fallacy? Because the person expects his or her argument to be taken as more credible than the run-of-the-mill argument -- not because the argument is more well-constructed or well-informed, but simply because of the identity (or rather, the former identity) of the person making the argument. It is invalid to treat arguments made by people-who-changed-their-minds as possessing some sort of extra credibility over the same arguments made by someone else.

Of course, like many logical fallacies, the "ab homine" is a fallacy only in the strictest sense. In the real world, what authors of the "ab homine" fallacy typically intend to imply is this: "The arguments for my current position are so overwhelmingly convincing that even I -- a former opponent -- was forced to switch sides." That might have some inferential weight. Or it might be quite interesting and relevant for other reasons if Bush or Kerry somehow fail to get the support of their own party's stalwarts.

But you can always find people changing their minds in any direction, many of whom do so for illogical reasons -- self-interest, peer pressure, misinformation, irrationality, whims. The mere fact that someone reached his position by changing his mind, in and of itself, shouldn't make his argument any more credible.

5 Comments:

Blogger Macht said...

I'd say that it is a Red Herring (in most cases) if what you used to believe is part of an argument for why you shouldn't believe it now. It might be useful to show how you once believed something and this is the thought process you took to arrive at your new belief. But strictly speaking, the fact that somebody is a life-long Republican is irrelevant to why somebody shouldn't vote for Bush.

11:12 AM  
Blogger LegalXXX said...

I think David Horowitz and David Brock both just spontaneously combusted.

1:47 PM  
Blogger nshumate said...

I note that you somehow restrained yourself from using EXMOs as an example.

6:04 PM  
Anonymous Anonymous said...

Well, it makes _some_ sense. In a time where being 'of the other side' makes you instantly ignorable, sometimes saying that you used to be one of the 'good guys' gets a foot in the door. Also, it shows that, maybe, you're not all bad-there's some good in you, somewhere!

12:45 AM  
Blogger Jeremy Pierce said...

In our current climate, we have all these conspiracy theorists who question the motives of anyone in the Republican party as trying to get their party to come out right but not basing their ideas on solid arguments. In that context, then, I might say that Joe Lieberman has no Republican axe to grind but thinks X. It's not an argument for X, and it's a fallacy to think that it is an argument for X, but that's not what I think people generally take it to be. It's a defeater of the hypothesis that the person is saying it only because of their political persuasion.

8:40 PM  

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