On 2/16/07, Carrol Cox <[log in to unmask]> wrote:
> Ad hominem:
> Q claims P
> Q is a jerk.
> Therefore P is false.
> Note: this _includes_ personal attack (Q is a jerk), but what makes it
> an ad hominem argument is that the attack on thed person is used to
> discredit the proposition. This is ALWAYS wrong, because true
> propositions can be maintained by shitheads without ubtruing the
> proposition.

The problem with the above argument is not that it is ad hominem, but that
the conclusion is too strong. Consider:

Q claims P
Q is a jerk (at least with respect to matters having to do with P)
Therefore, (in the absence of independent evidence) there is no reason to
take P seriously.

There doesn't seem to be anything wrong with that kind of argument to me.

When ad hominem arguments fail, it is because the dimension along which the
person is being attacked is irrelevant to their ability to judge the
evidence in the area that is under discussion. So bad ad hominem arguments
are really fallacies of irrelevance. But there are perfectly OK ad hominem
arguments that don't commit the fallacy of irrelevance.

Q claims to have been an eye witness to X.
Q is a notorious drunk.
Therefore, Q's testimony about X should not be taken seriously.

Conversely, there is nothing wrong with an appropriate appeal to authority
(another form of argument that texts on informal logic typically classify as
fallacious). If the individual in question really is an authority on certain
questions, there is nothing wrong with accepting their judgment about such
matters. In fact, since scientific inquiry is a social, not an indiviual,
enterprise, it would grind to a halt if we did not behave in this way.