Sometimes people ask me for examples of ad hominems and I have trouble finding nice clean examples. I've written about this here. (A couple of commenters pointed out that the example I gave is an example of poisoning the well which is a form of ad hominem.
But in perusing comments on EconLog in the last few days, I think I've found a fairly straightforward example. And this example is from a generally civil commenter whom I've often disagreed with, but who, if I met him, I think I would probably like. So that makes it an even better example than otherwise because it's easy to accuse people of ad hominems when they're nasty or uncivil.
Perhaps I would take [Bryan] Caplan a little more seriously were he to resign his position at a state funded university and move to one that is fully supported by private funds. After all, if public funding of education is not worth the investment, why is he taking a salary from taxpayers and perpetuating the problem? I've been troubled by his writings on this topic but then I'm one who has been a staunch supporter of public education as I saw the benefits that my parents accrued and both of my degrees came from state universities.
Alan is judging the quality of Bryan's arguments in part on the fact that he takes taxpayer money as an educator while advocating the ending or substantial reduction in the use of taxpayer money in education. But Bryan's augment has to be judged on logic, on reason, and on data. I'm about at page 115 now and I've read every footnote and I'm impressed. I can't think of a single sentence so far where the fact that Bryan takes taxpayer money should affect how I evaluate that sentence.
Moreover, there's a deep irony in Alan's using this particular ad hominem. If one were to judge Bryan's argument by his taking taxpayer money--and I emphasize that I don't advocate doing that--one would have to put more weight, not less, on his argument. Why? Incentives. Commenter BC said it best, in response to Alan:
Hmmm. Any employee of a state-funded university faces a conflict of interest in writing about education subsidies because they benefit from those subsidies. (A subsidy nominally given to a student that must spend that subsidy at a university is actually a subsidy for the university.) Yet, Caplan is willing to argue against such subsidies, so I'm not sure why you wouldn't take his views seriously. Those employees that argue *in favor* of their subsidies are the ones who may be conflicted.
If a tobacco company researcher found that smoking causes cancer, wouldn't you take him seriously? It's the tobacco company researchers that claim smoking doesn't cause cancer that may be conflicted.