An ad hominem (Latin for "to the man" or "to the person"), short for argumentum ad hominem, is an argument made personally against an opponent instead of against their argument. Ad hominem reasoning is normally described as an informal fallacy, more precisely an irrelevance.
Ad hominem 
In Latin, the word homō (of which hominem is the accusative case) has the gender-neutral meaning of "a human being", "a person" (unlike some of the words in Romance languages it gave rise to, such as French homme and Italian uomo). A translation of ad hominem that preserves this gender-neutrality is "to the person". Ad hominem is an attack on the person, not the person's arguments, though mere verbal abuse in the absence of an argument, however, is not ad hominem nor any kind of logical fallacy.
Ad hominem circumstantial points out that someone is in circumstances such that they are 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).
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.
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 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 is certainly no less likely to deny an affair that never happened.
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.
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.
Attributing minor properties 
A subtle way of ad hominem is attributing minor properties that are hard to argue because of their subjective nature. This type of ad hominem distinguishes itself from other forms by not being the base of the argument, but rather subtly implying such properties exist. This method of ad hominem is usually used to further convince something is true, without being the essential point of the argument, therefore a valid argument could contain this type of ad hominem. In other cases, attributing negative qualities to people or ideas can be used to further confirm oneself's beliefs even though the qualities have no relevance to the belief or idea.
Halo effect 
See also; List of cognitive biases
Ad hominem arguments work via the halo effect, a human cognitive bias in which the perception of one trait is influenced by the perception of an unrelated trait, e.g. treating an attractive person as more intelligent or more honest. People tend to see others as tending to be all good or tending to be all bad. Thus, if you can attribute a bad trait to your opponent, others will tend to doubt the quality of their arguments, even if the bad trait is irrelevant to the arguments.
Questions about the notion of an ad hominem fallacy 
Doug Walton, Canadian academic and author, has argued that ad hominem reasoning is not always fallacious, and that in some instances, questions of personal conduct, character, motives, etc., are legitimate and relevant to the issue, as when it directly involves hypocrisy, or actions contradicting the subject's words.
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.
Olavo de Carvalho, a Brazilian philosopher, has argued that ad hominem reasoning not only has rhetorical, but also logical value. As an example, he cites Karl Marx's idea that only the proletariat has an objective view of history. If that were to be taken rigorously, an ad hominem argument would effectively render Marx's general theory as incoherent: as Marx was not a proletarian, his own view of history couldn't be objective.
See also 
- And you are lynching Negroes
- Appeal to authority
- Association fallacy
- Character assassination
- Discrediting tactic
- Fair Game (Scientology)
- Fundamental attribution error
- Hostile witness
- List of logical fallacies
- Negative campaigning
- Poisoning the well
- Self-hating Jew
- Shooting the messenger
- The Art of Being Right
- "Ad hominem". The Free Merriam-Webster Dictionary. Merriam-Webster, Incorporated. Retrieved 19 February 2013.
- "ad hominem: West's Encyclopedia of American Law". Answers.com. 2007-09-10. Archived from the original on 12 October 2009. Retrieved 2009-11-08.
- Walton, Douglas (2008). Informal Logic: A Pragmatic Approach. Cambridge University Press. p. 190.
- Bowell, Tracy; Kemp, Gary (2010). Critical Thinking: A Concise Guide. Abingdon, Oxon: Routledge. pp. 210–213. ISBN 0-415-47183-4.
- Copi, Irving M. (1986). Informal Logic. Macmillan. pp. 112–113. ISBN 0-02-324940-4.
- "AdHominem". Drury.edu. Archived from the original on 11 December 2009. Retrieved 2009-11-08.
- "ad hominem". The American Heritage Dictionary of the English Language (Fourth ed.). 2000 (updated in 2009).
- Walton, Douglas (1998). Ad Hominem Arguments. University of Alabama Press. pp. 18–21. ISBN 0-8173-0922-5.
- Curtis, Gary N. "Argumentum ad Hominem". Fallacy Files. Archived from the original on 20 September 2007. Retrieved 2007-09-10.
- Walton, Douglas (2008). Informal Logic: A Pragmatic Approach. Cambridge University Press. p. 170.
- Taylor, Charles (1997). "Explanation and Practical Reason". Philosophical Arguments. Harvard University Press. pp. 34–60.
Further reading 
- Hurley, Patrick (2000). A Concise Introduction to Logic (7th ed.). Wadsworth. pp. 125–128, 182. ISBN 0-534-52006-5.
- Copi, Irving M.; Cohen, Carl. Introduction to Logic (8th ed.). pp. 97–100.
- Walton, Douglas (1998). Ad Hominem Arguments. Tuscaloosa: University Alabama Press.
|Look up ad hominem in Wiktionary, the free dictionary.|
- Carl Sagan: The Demon-Haunted World http://en.wikipedia.org/wiki/The_Demon-Haunted_World]
- Ad hominem at PhilPapers
- Nizkor.org: Fallacy: Ad Hominem.
- Nizkor.org: Fallacy: Circumstantial Ad Hominem.
- Argumentum Ad Hominem
- PDF (70.2 KB)
- Logical Fallacies: Ad Hominem
- Mission Critical: Introduction to Ad Hominem Fallacies