What is 'ad hominem argument'?
n ad hominem argument, also known as argumentum ad hominem (Latin,
literally "argument against the person") or attacking the
messenger, involves replying to an argument or assertion by
attacking the person presenting the argument or assertion rather
than the argument itself. It is usually, though not always, a
logical fallacy (see Validity below).
(http://en.wikipedia.org/wiki/Ad_hominem
" Ad hominem as logical fallacy
A (fallacious) ad hominem argument has the basic form:
A makes claim X.
There is something objectionable about A.
Therefore claim X is false.
The first statement is called a 'factual claim' and is the pivot
point of much debate. The last statement is referred to as an
'inferential claim' and represents the reasoning process. There
are two types of inferential claim, explicit and implicit.
Ad hominem is one of the best-known of the logical fallacies
usually enumerated in introductory logic and critical thinking
textbooks. Both the fallacy itself, and accusations of having
committed it, are often brandished in actual discourse (see also
Argument from fallacy). As a technique of rhetoric, it is powerful
and used often, despite its inherent incorrectness.
In contrast, an argument that instead relies (fallaciously) on the
positive aspects of the person arguing the case is sometimes known
as "positive ad hominem," or appeal to authority.
An ad hominem fallacy consists of asserting that someone's
argument is wrong and/or he is wrong to argue at all purely
because of something discreditable/not-authoritative about the
person or those persons cited by him rather than addressing the
soundness of the argument itself. The implication is that the
person's argument and/or ability to argue correctly lacks
authority. Merely insulting another person in the middle of
otherwise rational discourse does not necessarily constitute an ad
hominem fallacy. It must be clear that the purpose of the
characterization is to discredit the person offering the argument,
and, specifically, to invite others to discount his arguments. In
the past, the term ad hominem was sometimes used more literally,
to describe an argument that was based on an individual, or to
describe any personal attack. However, this is not how the meaning
of the term is typically introduced in modern logic and rhetoric
textbooks, and logicians and rhetoricians are in agreement that
this use is incorrect.
Examples:
"You claim that this man is innocent, but you cannot be trusted
since you are a criminal, as well."
"You feel that abortion should be illegal, but I disagree, because
you are uneducated and poor."
"Only right-wing nutjobs believe that homosexuals account for one
to two percent of the population."
Not all ad hominem attacks are insulting:
Example:
"Paula says the umpire made the correct call, but this is false,
because Paula is too important to pay attention to the game."
This is an ad hominem fallacy, even though it is saying something
positive about the person, because it is addressing the person and
not the topic in dispute.
Ironically, accusing an opponent of ad hominem can itself be an
example of ad hominem if it is worded as an insult: "I'm not going
to stand here and let him insult me!" or "My opponent is resorting
to logical fallacy to win," or "Since he is out of good arguments,
he's attacking me." (partial Argument from silence)"
--- wikipedia entry http://en.wikipedia.org/wiki/Ad_hominem