An ad hominem (Latin: “to the man”), short for argumentum ad hominem, is an attempt to link the truth of a claim to a negative characteristic or belief of the person advocating it.^[1]The ad hominem is normally described as a logical fallacy,^[2][3][4] but it is not always fallacious; in some instances, questions of personal conduct, character, motives, etc., are legitimate and relevant to the issue.^[5]

The philosopher Charles Taylor has argued that ad hominem reasoning is essential to understanding certain moral issues, and contrasts this sort of reasoning with the apodictic reasoning of philosophical naturalism.^[6]

Types

Abusive

Abusive ad hominem (also called personal abuse or personal attacks) usually involves insulting or belittling one’s opponent in order to attack his claim or invalidate his argument, but can also involve pointing out factual but apparent character flaws or actions that are irrelevant to the opponent’s argument. This tactic is logically fallacious because insults and negative facts about the opponent’s personal character have nothing to do with the logical merits of the opponent’s arguments or assertions.

Examples:

• “You can’t believe Jack when he says the proposed policy would help the economy. He doesn’t even have a job.”
• “Candidate Jane’s proposal about zoning is ridiculous. She was caught cheating on her taxes in 2003.”
• “Jeff’s argument on LeBron James’ failures in the NBA finals aren’t worth reading, everyone knows he is a “LeBron” hater.”

An abusive ad hominem can apply to a judgment of cultural works or academic efforts based on the behavior or unconventional political beliefs of an artist, author, or musician, or the taste of an infamous person who loved a certain work.

Examples:

• Jimi Hendrix died of a drug overdose, so his music was worthless.
• Leni Riefenstahl was a Nazi, so her film The Triumph of the Will is devoid of merit.
• Sylvia Plath was a depressive who eventually committed suicide, so her works are unreadable.
• That Boris Godunov was the favorite opera of Joseph Stalin indicates the worthlessness of the opera.
• What Ted Kaczynski wrote about boundary conditions in mathematics is shown false due to his crimes.

Circumstantial

Ad hominem circumstantial points out that someone is in circumstances such that he is disposed to take a particular position. Ad hominem circumstantial constitutes an attack on the bias of a source. This is fallacious because a disposition to make a certain argument does not make the argument false; this overlaps with the genetic fallacy (an argument that a claim is incorrect due to its source).^[7]

The circumstantial fallacy applies only where the source taking a position is only making a logical argument from premises that are generally accepted. Where the source seeks to convince an audience of the truth of a premise by a claim of authority or by personal observation, observation of their circumstances may reduce the evidentiary weight of the claims, sometimes to zero.^[8]

Examples:

Mandy Rice-Davies’s famous testimony during the Profumo Affair, “Well, he would [say that], wouldn’t he?”, is an example of a valid circumstantial argument. Her point was that since a man in a prominent position, accused of an affair with a callgirl, would deny the claim whether it was true or false. His denial, in itself, carries little evidential weight against the claim of an affair. Note, however, that this argument is valid only insofar as it devalues the denial; it does not bolster the original claim. To construe evidentiary invalidation of the denial as evidentiary validation of the original claim is fallacious (on several different bases, including that of argumentum ad hominem); however likely the man in question would be to deny an affair that did in fact happen, he could only be more likely to deny an affair that never did.

Conflict of Interest: Where a source seeks to convince by a claim of authority or by personal observation, identification of conflicts of interest are not ad hominem – it is generally well accepted that an “authority” needs to be objective and impartial, and that an audience can only evaluate information from a source if they know about conflicts of interest that may affect the objectivity of the source. Identification of a conflict of interest is appropriate, and concealment of a conflict of interest is a problem.

Tu quoque

Ad hominem tu quoque (literally: “You also”) refers to a claim that the source making the argument has spoken or acted in a way inconsistent with the argument. In particular, if Source A criticizes the actions of Source B, a tu quoque response is that Source A has acted in the same way. This argument is fallacious because it does not disprove the argument; if the premise is true then Source A may be a hypocrite, but this does not make the statement less credible from a logical perspective. Indeed, Source A may be in a position to provide personal testimony to support the argument.

For example, a father may tell his son not to start smoking as he will regret it when he is older, and the son may point out that his father is or was a smoker. This does not alter the fact that his son may regret smoking when he is older.

Guilt by association

Guilt by association can sometimes also be a type of ad hominem fallacy if the argument attacks a source because of the similarity between the views of someone making an argument and other proponents of the argument.^[7]

This form of the argument is as follows:

Source S makes claim C.

Group G, which is currently viewed negatively by the recipient, also makes claim C.

Therefore, source S is viewed by the recipient of the claim as associated to the group G and inherits how negatively viewed it is.

Common misconceptions

Gratuitous verbal abuse or “name-calling” itself is not an ad hominem or a logical fallacy.^{[8][9][10][11][12]}

In order to become a fallacy, the insult would need to be given as a reason for believing some conclusion. An example would be, “X is idiotically ignorant [of politics], so why should we listen to him now?”

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*From Wikipedia.