Ad hominem

Ad hominem as logical fallacy

A traditional, regular (fallacious) ad hominem argument was identified by Aristotle in his On Sophistical Refutations and has the basic form:

Regular Ad Hominem

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

Inverted Ad Hominem

1. A makes claim B;
2. there is something desirable about A,
3. therefore claim B is true.

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 inverted ad hominem fallacy consists of saying that someone's argument is correct and/or they are correct to argue at all purely because of something creditable/authoritative about the person or those persons cited by them rather than the argument itself. The implication is that the person need not even bother to defend against an attack on the soundness of his arguments because of this very credibility/authority. The other implication which can be seen as either leading to or following from the preceding implication, being that a potential opposing interlocutor lacks this very same credibility/authority (regular ad hominem). This "appeal to authority" and/or implied "appeal to authority-lacking" leaves the fallacymonger in a serious bind as it also implies a hidden premise which itself defeats his diversionary sub-argument about his own authority. This premise may then be 'granted' by any victim of this fallacy and her argument - at least regarding the fallacious sub-argument - is all but made.

Bind example: A recognizably credentialed professional logician (Fallacymonger) vs. a layperson (Fallacymongered): Note: In this example both the appeal to authority and authority-lacking are explicitly stated for the sake of clarity. In reality, the value of the introduction of the term Inverted Ad Hominem was to emphasise the often offensive yet subtle implication and nature of a fallacious Appeal to Authority.

Fallacymonger: "You are wrong to argue with me about matters of logic because I am an expert in this field. Because you lack this expertise yourself, I refuse to waste my time arguing with you at all about this matter."

Note: Expediency can be a good reason if actually based in reason to non-fallaciously "appeal to authority". One might reasonably expect the fallacymonger would have done better (diplomatically and logically) to excuse himself claiming "a lack of time - trust my expertise for now", rather than the antagonistic "a waste of time". Perhaps though, time was so short for him that he had not even enough time to reason this much.

Fallacymongered: "I will grant you this premise: That I would have to be a fool to argue that you are wrong in this regard simply because most, if not all, professional logicians agree that an 'appeal to authority' of this sort is a fallacy."

By granting this premise the fallacymongered acknowledges and forces the fallacymonger likewise to acknowledge A) he is already arguing with her and B) a willingness to argue from first principles if required, in order to make their respective cases. She must still present a sound argument, but so must the fallacymonger. Note that if he rejects her offer of the granted premise then he acknowledges, A) her right to cite his own peers to establish the fallaciousness of his argument or B) her right to ignore likewise the rules of logic, and so assume authority fallaciously herself (which of course leads to absurdity). But if he accepts the granted premise then, he has defeated himself undoubtedly, for he acknowledges that he would have to be a fool himself to use his own expertise in this way. Either way she has established her right to question his authority and his need to defend his authority logically. Note also that in this example the fallacymonger is also fallaciously begging the question by claiming his authority by appealing to his own authority and, has introduced a red herring by shifting the argument from being about; "matters of logic" to one about; themselves and his "expertise" and her "lack" thereof. It has become an argument about the argument which is understandable given that it was initially about "matters of logic". But his position became fallacious when he made it an argument about the arguers about the argument, even though the point of doing so seems to be about their status' as logicians or not. Regarding a logician's last argument it would seem that his/her status is only as relevant and valid as is his last argument.

This is of course a rather silly example, but unfortunately it is in principle a common situation. One need only consider the circular arguments of someone defending his religion by invoking the authority of the God of that same religion to defend the authority of the church, bible and other artifacts of that very same religion which, in turn the authority of, are used to defend the authority of that same God and the artifacts themselves - not to mention his own authority. This is of course an inversion of the all too common regular (fallacious) ad hominem arguments of those who discredit secular views as evil and, claim those views are therefore invalid. (Inverted Ad Hominem is a term first coined by Layman at The Brights Forums. A bright being a person whose worldview is naturalistic.)

Conversely, not all regular ad hominem attacks are insulting. "Paula says it is impossible for her to murder a man, but this is false because Paula has never lost her temper." Nor likewise are all inverted ad hominem defenses self flattering - "I say it is impossible for me to murder a man, and this is true because I often lose my temper."

Subtypes

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

Ad hominem abusive

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

Person A: There is a God and archealogical records of the Middle East proves it.

Person B: Well, that's what I'd expect a fundamentalist Christian to say.

Ad hominem circumstantial

"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."

The Mandy Rice-Davies ploy, "Well, he would [say that], wouldn't he?" is a superb use of this fallacy.

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

"You say airplanes are able to fly because of the laws of physics, but this is false because earlier you said airplanes fly because of magic."

"You cannot accuse me of libel because what you do is libel as well."

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

Taxonomy

This form of 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.

Valid Ad Hominem

The second form of the ad hominem was identified by John Locke in his An Essay Concerning Human Understanding, when he wrote that it was

to press a man with consequences drawn from his own principles or concessions. This is already known under the name of argumentum ad hominem.

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
   

   See also

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

Ad Hominem is also a NSBM band from France. Look here for more info.