Ad hominem
Identification
An ad hominem argument, also known as argumentum ad hominem (Latin, literally "argument against the man"), is a fallacy that involves replying to an argument or assertion by attempting to discredit the person offering the argument or assertion. 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. As technique of rhetoric, despite its usual lack of subtlety, it is powerful and used often.Usage
Properly understood, it consists of saying that someone's argument is wrong because of something about the person rather than about the argument. Thus, for example, merely insulting another person in the middle of otherwise rational discourse does not necessarily constitute ad hominem, as this term has usually been taught. Moreover, it is not necessary to insult the person whose argument is attacked in order to commit the ad hominem fallacy. For example, one could say "George W. Bush is a Republican; therefore, the argument he just gave is wrong." That is fallacious because the argument should be judged on its merits independently of who stated it; it is ad hominem according to the definition above, and George W. Bush would probably not consider it insulting to be called a Republican.Rather, 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. To be sure, however, the term is often used as a synonym for "insulting one's opponent in the middle of otherwise rational discourse." But this is not how the meaning of the term is typically introduced in logic and rhetoric textbooks, and logicians and rhetoricians are widely agreed that this use is incorrect.
Three traditionally identified varieties include ad hominem abusive, ad hominem circumstantial, and ad hominem tu quoque.
An example: "I obviously don't need to reply to Jones's arguments about creationism; everyone knows that he's a convicted felon."
For example: "You needn't bother to listen to the trial arguments of the tobacco companies; after all, they're just defending their own multi-million-dollar financial interests."
It is important to note that the above argument is not irrational, although it is not correct in strict logic. This illustrates one of the differences between rationality and logic.
An example: "You claim to be a fundamentalist Christian yet you support gay rights."
The tu quoque form is often a specific kind of the two wrongs make a right fallacy.
The argumentum ad hominem is a genetic fallacy and red herring. Argumentum ad hominem includes poisoning the well.Ad hominem abusive
Ad hominem abusive (also called argumentum ad personam) usually and most notoriously involves merely (and often unfairly) insulting one's opponent, but can also involve pointing out factual but damning character flaws or actions. The reason that this is fallacious is that--usually, anyway--insults and even damaging facts simply do not undermine what logical support there might be for one's opponent's arguments or assertions. Ad hominem circumstantial
Ad hominem circumstantial involves pointing out that someone is in circumstances such that he or she is disposed to take a particular position. Essentially, circumstantial ad hominem constitutes an attack on the bias of a person. The reason that this is fallacious is that it simply does not make one's opponent's arguments, from a logical point of view, any less credible to point out that one's opponent is disposed to argue that way. Ad hominem tu quoque
Ad hominem tu quoque (literally, "at the person, you too") could be called the "hypocrisy" argument. It occurs when a claim is dismissed either because it is inconsistent with other claims that the claimant is making or because it is inconsistent with the claimant's actions.