The Ad Hominem Fallacy

The ad hominem fallacy might be one of the more well known fallacies, in the sense that people are often more likely to recognize the title and its meaning than they are to know the titles of other fallacies like the non sequitur.  Sometimes confusion reigns as to what exactly an ad hominem is and isn't, despite this public familiarity with the phrase.  Harsh words, accusations of intellectual or moral deficiencies, and even insults are not ad hominems on their own; what makes something an ad hominem is how it is used in relation to other claims.

For instance, when I use harsh words (sometimes very harsh words) to refer to people who believe in self-refuting impossibilities or refuse to abandon stupid or false ideas after being presented with refutations, I am not committing the ad hominem fallacy.  If I was to say that someone is wrong on a point because he/she is a supposedly terrible person or because that person is wrong about something else, then I would be committing the ad hominem fallacy, but nothing else actually qualifies.  Just because a person is heinous or is fallacious elsewhere does not mean that he or she is also heinous or fallacious in another area.

It is not necessarily an ad hominem when someone disparages the character of another person.  In fact, condemning or exposing the poor intellectual or moral character of a person can be of great value--as long as it is not held up as the basis for a red herring or non sequitur.  Someone guilty of an intellectual or moral offense should be called out, in a very harsh manner if necessary.  But using an exposure or condemnation in a fallacious way is inherently irrational.

An ad hominem might take the following forms:

1.  George is stupid.
2.  Therefore what George is saying right now must be false.

1.  Haley was always wrong about her predictions in the past.
2.  Therefore Haley will be wrong about her latest prediction.

1.  I don't like Jacob.
2.  Therefore Jacob is not right.

Clearly, it does not follow from someone being stupid or having been wrong in the past that their most current claim is false.  No one can legitimately toss aside an idea just because the claimer has been wrong before or is typically unintelligent.  No one can legitimately discard a claim just because they don't like the person discussing the idea.  To do so would be fallacious because one would reject a concept or claim not on the basis of proof, but because of some irrelevant factor, and perhaps even a slanderous one.

Saying that Hitler can't possibly be correct about some economic or historical matter would be an example of the ad hominem fallacy.  Attacking a person in a debate while completely ignoring that person's claims would be an example of the ad hominem fallacy.  But insults, however vicious, are not in themselves ad hominems.  A charge meant as an insult might even be factually true.  However, this does not and cannot justify misrepresenting someone, asserting further deformity of character where there is none, or treating someone as if nothing they say could possibly be correct.