ad hominem : Java Glossary

Translated from Latin to English, Ad Hominem means against the man or against the person.

An Ad Hominem is a general category of fallacies in which a claim or argument is rejected on the basis of some irrelevant fact about the author of or the person presenting the claim or argument. Typically, this fallacy involves two steps. First, an attack against the character of person making the claim, her circumstances, or her actions is made (or the character, circumstances, or actions of the person reporting the claim). Second, this attack is taken to be evidence against the claim or argument the person in question is making (or presenting). This type of argument has the following form:

1. Person A makes claim X.
2. Person B makes an attack on person A.
3. Therefore A’s claim is false.

The reason why an Ad Hominem (of any kind) is a fallacy is that the character, circumstances, or actions of a person do not (in most cases) have a bearing on the truth or falsity of the claim being made (or the quality of the argument being made).

Closely related to the Ad Hominem is the personal attack.

1. Person A makes claim X.
2. Person B can’t think anything to rebut the claim, so he tries to change the subject by insulting A, hoping this will derail the discussion away from the embarrassing area. Most A’s will fall for the trap, rushing to defend themselves.
3. Unlike a standard Ad Hominem, B makes no claim that A’s original assertion is thus false because of the insult.