On 2/16/07, Phil Gasper <[log in to unmask]> wrote:

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.

--PG