Originally posted by divegeesterNo, actually.
If I said "nothing you say has any credibility because you are a blithering, tub-thumping motormouth", would that be an ad hominem?
You are not saying that he is wrong, you are saying he is not credible.
And credibility can indeed be lost by being a "blithering, tub-thumping
motormouth".
Now if someone were to make a logical argument, and you were to say that
they are wrong because they are [insert derogatory term here] then that
would be an ad hominem fallacy.
However if they were to make an assertion that something was true, and
you pointed out that they lacked sufficient credibility or trustworthiness
to make that assertion and be believed without providing supporting
evidence and/or logical argument then you are not actually committing
an ad hominem fallacy.
http://plover.net/~bonds/adhominem.html