Ad hominem

An ad hominem argument, also known as argumentum ad hominem (Latin, literally "argument to the man"), is a logical fallacy that involves replying to an argument or assertion by addressing the person presenting the argument or assertion rather than the argument itself. A (fallacious) ad hominem argument has the basic form:

1. A makes claim B;
2. there is something objectionable about A,
3. therefore claim B is false.

The first statement is called a 'factual claim' and is the pivot point of much debate. The last statment is referred to as an 'inferential claim' and represents the reasoning process. There are two types of inferential claim, explicit and implicit. Positive arguments to the person are discussed under appeal to authority.

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 a technique of rhetoric, it is powerful and used often, despite its lack of subtlety.

Usage

An ad hominem fallacy consists of saying that someone's argument is wrong purely because of something about the person rather than about the argument itself. 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. But this is not how the meaning of the term is typically introduced in modern logic and rhetoric textbooks, and logicians and rhetoricians are widely agreed that this use is incorrect.

Conversely, not all ad hominem attacks are insulting. "Paula says it is impossible to murder a man, but this is false because Paula never loses her temper."

Validity

Ad hominem is fallacious when applied to deduction, and not the evidence (or premise) of an argument. Evidence may be doubted or rejected based on the source for reasons of credibility, but to doubt or reject a deduction based on the source is the ad hominem fallacy.

Premises discrediting the person can exist in valid arguments, when the person being criticized is the sole source for a piece of evidence used in one of his arguments.

1. A committed perjury when he said Q
2. We should not accept testimony for which perjury was committed
3. therefore, A 's testimony for Q should be rejected

Subtypes

Three traditionally identified varieties include ad hominem abusive, ad hominem circumstantial, and ad hominem tu quoque.

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.

An example: "Jack is wrong when he says there is no God because he is a convicted felon."

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.

"Tobacco company representatives are wrong when they say smoking doesn't seriously affect your health, because 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.

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.

"You say airplanes fly because of physics, but this is false because you said earlier airplanes fly because of magic."

The tu quoque form is often a specific kind of the two wrongs make a right fallacy.

Taxonomy

The argumentum ad hominem is a genetic fallacy and red herring, and is often but not necessarily an appeal to emotion. Argumentum ad hominem includes poisoning the well.

See also

• fundamental attribution error
• validity
• "And you are lynching Negroes"

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