Ad hominem (Latin for "to the man" or "to the person"), short for argumentum ad hominem, is now usually understood as a logical fallacy in which an argument is rebutted by attacking the character, motive, or other attribute of the person making the argument, or persons associated with the argument, rather than attacking the substance of the argument itself.
However, its original meaning was an argument "calculated to appeal to the person addressed more than to impartial reason" 
However, in some cases, ad hominem attacks can be non-fallacious; i.e., if the attack on the character of the person is directly tackling the argument itself. For example, if the truth of the argument relies on the truthfulness of the person making the argument—rather than known facts—then pointing out that the person has previously lied is not a fallacious argument.
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 false because it does not disprove the premise; 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.
Circumstantial ad hominem points out that someone is in circumstances such that they are disposed to take a particular position. It 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 does not apply where the source is taking a position by using a logical argument based solely on 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, "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, provides little evidence against the claim of an affair.
- Note well, however, that this argument is valid only insofar as it devalues the denial; it does not strengthen the original claim. To construe invalid evidence of the denial as valid evidence of the original claim is fallacious (on several different bases, including that of argumentum ad hominem and appeal to emotions); however likely the man in question would be to deny an affair that did in fact happen, he is even more likely to deny an affair that never happened. (For example, inferring guilt from a denial – or, less starkly, excessive devaluation of a denial – is a very common feature in conspiracy theories, witch-hunts, show trials, struggle sessions, and other coercive circumstances in which the person targeted is presumed guilty.)
- Glassner suggests that Bennett is somehow unqualified to criticize rap music because of positions Bennett has taken on other issues. However wrong Bennett may have been on other issues, such as the funding of public television or illegitimacy, that does not mean that his criticisms of rap were mistaken.
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.
An example of this fallacy could be "My opponent for office just received an endorsement from the Puppy Haters Association. Is that the sort of person you would want to vote for?"
When a statement is challenged by making an ad hominem attack on its author, it is important to draw a distinction between whether the statement in question was an argument or a statement of fact (testimony). In the latter case the issues of the credibility of the person making the statement may be crucial.
Criticism as a 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 (discussing facts about the speaker or author relative to the value of his statements) is essential to understanding certain moral issues due to the connection between individual persons and morality (or moral claims), and contrasts this sort of reasoning with the apodictic reasoning (involving facts beyond dispute or clearly established) of philosophical naturalism.
- "And you are lynching Negroes"
- Appeal to authority
- Appeal to emotion
- Appeal to motive
- Association fallacy
- Character assassination
- Discrediting tactic
- Fair Game (Scientology)
- Fundamental attribution error
- Hostile witness
- Negative campaigning
- Poisoning the well
- Race card
- Red herring
- Shooting the messenger
- Smear campaign
- Straw man
- Tone policing
- The Art of Being Right
- "Ad hominem". Merriam-Webster. Merriam-Webster, Incorporated. Retrieved 19 February 2013.
- Dr. Michael C. Labossiere (2002–2010). "42 Fallacies: Ad Hominem" (PDF). p. 2. Retrieved 2013-10-17.
- Fowler, H. W. (1926), A Dictionary of Modern English Usage (under Technical Terms)
- 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.
- 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 (1995). "Explanation and Practical Reason". Philosophical Arguments. Harvard University Press. pp. 34–60. ISBN 9780674664760.
- 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.
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