Ad Hominem

""If a crazy serial killer who believes he is surrounded by Teletubbies argues that if you drop a ball, it'll fall to the ground, because gravity will pull the ball towards the Earth, is he wrong? Do the arguments become less valid because you think there's something wrong with the person behind the arguments? Will the ball start falling upwards from now on?""

- Dendrophilian of YouTube

See Idea Channel's explanation of the fallacy here.

You're an Ad Hominem Fallacy!!

Refuting an argument by attacking some aspect of the presentation of it, rather than addressing the content of the argument itself. It can consist of an attack on the person making the argument; the source of their information; their circumstances; their previous position; a discrepancy between their actions and their argument; or the style in which the argument is presented.

Ad hominem is very often mistakenly claimed in cases where an argument's opponent attacks its proponent in addition to presenting a valid counterargument. "You're stupid, therefore your argument is invalid" is an ad hominem; "your argument is invalid, therefore you're stupid" (or "Your argument is invalid and you're stupid") is not. Similarly, some people seem to think that Ad Hominem is necessarily abusive, which it isn't. "You've used the 'Four Terms' fallacy, you stupid retard, therefore you're using faulty logic" is not Ad Hominem. "Mike has clearly put a lot of thought into whether we should buy a pool, but he is a convicted felon" is.

A key point is whether the unflattering accusation about the person is relevant to the topic at hand. However, this is on a sliding scale as arguments or statements can stand on their own merit.

Direct ad hominem
The attack is made directly on the person making the argument. Here's a standard hypothetical example:

"Adolf Hitler: This is an irresponsible fiscal policy because the budget deficit is too great. Politician: I won't listen to you! You're Hitler!"

While Hitler certainly wasn't a nice person, that in itself is unrelated to the logical validity of any arguments he makes. This extends to a degree in situations where the ad hominem attack itself is related to the argument; if the supposition comes from a source that is known for fallibility or may have a reason to be biased, it should be treated with healthy skepticism, but not assumed to be false.

"The Weekly World News says that George Washington was the first president of the United States."

It would be quite logically sound to say "why should we take their word for it; they're unreliable!" It is not sound, however, to say that the above statement must be false, because despite the fact that the Weekly World News was noted for being full of made-up stories, George Washington was the first President of the United States.

Examples

 * Most people can recognize a simplistic ad hominem attack as humorous, but that didn't stop DirecTv from flipping out at a spot by Time Warner asserting that "DirecTv hates puppies"

Looks like this fallacy but is not
""I studied law at Harvard, and I can see that this law is clearly unconstitutional." "You studied law at Harvard, but you never got a degree.""
 * When the rebuttal is insulting but valid: "You can't be a member of Mensa as you claim, because your IQ tests indicate that your IQ is 70".
 * When an insult is present but is not used as a component of a logical argument. Simply saying "You are an idiot" is not polite, but unless there's a "therefore" step to a conclusion, it is not a fallacy.
 * When it is in response to an explicit or implicit appeal to the authority of the speaker:


 * The validity of this counterargument can be summarized thusly: "your credentials aren't as impressive as you say, so you're going to have to prove that rather than tell us to take your word for it."

Circumstantial ad hominem
When the circumstances of the arguer are held to affect the truth of the argument. It's frequently rolled out against people who have any kind of motive for making their argument (the "he would say that, wouldn't he?" defense), often intended to imply that "he" is an incredibly selfish/malicious person for even looking at the idea with an open mind. In reality, it's more unreasonable to expect someone to have no reason to hold their viewpoint; their vested interest does not automatically invalidate their criticism.

"Bob: "This bill will be expensive and will not work, therefore you should vote against it." Alice: "Bob is employed by a company which stands to lose money from this bill, therefore Bob will lose money and perhaps his job if this bill passes. Of course he would oppose it.""

Poisoning the Well
This fallacy can be one of two types, either discrediting the opponent before they even begin to make their argument, usually by a direct ad hominem against them ("And might I just remind the audience before Alice speaks that she is a convicted felon?") or by calling the validity of their sources or standing into question after they have made their argument. More or less the converse of Appeal to Authority; here, the attempt is to make an audience reject a claim because of the speaker's alleged lack of authority.

""You'll find Bob talks about law an awful lot for a guy who got his degree from Eastern Iowa State University.""

The attempt here is to preemptively discredit Bob's standing as a lawyer not on the basis of what he's actually saying, but on where he was schooled.

The most pernicious manifestation is where where entire groups are potentially shut out of the discussion:


 * Men can't talk about abortion because they don't get pregnant
 * American whites can't talk about slavery because they never experienced it.

This seems like an example, but is actually a different problem of logic:

""You cited the Encyclopedia Britannica. A recent study found that Encyclopedia Britannica had 123 errors of fact -- in only 42 articles.""

As a reply to "This fact is true because the Encyclopedia Britannica states as much," this has a sound logical basis; because the cited reason to believe the statement is the credibility of the encyclopedia, an attack on its credibility is relevant and therefore not an ad hominem. What it is, in fact, is a misleading citation of statistics; these factual errors could be minor misspellings of titles that all occurred in one mistranslated article, for example.

Examples

 * Most accusations of White Knighting are intended to discredit the accused by making it seem as if they have a self-interested reason to hold their stated position. While this may be true, it does not make said position any less valid.

Tu quoque ("You, too!")

 * Another type of Ad Hominem, Tu Quoque refers to the attempt to deny an argument by asserting that the person presenting the argument either suffers from the same flaw (i.e. they do not practice what they preach) or has held an opposing view in the past. The fact that such a person is a Hypocrite if he criticizes others for bearing the same flaw he does does not invalidate or is not related to his line of reasoning in condemning that flaw.

"Bob: "Smoking is a highly addictive habit and causes health problems. You should not smoke." Alice: "But you yourself smoke!""

The fact that Bob is a smoker doesn't mean that he is wrong about the effects of smoking. Still confused? Perhaps Bob knows full well about the dangers of smoking, but continues to do it.

"Bob: "This bill will be expensive and will not work, therefore you should vote against it." Alice: "But you supported the bill last month!""

Bob's new argument is not invalidated by any previous position he may have held. A logically sound counterargument would be to restate the reasoning behind Bob's previous position to him and ask why he changed his mind from that line of thinking.

Examples
"When the facts change, I change my mind. What do you do, sir?"
 * This is a favorite tactic of politicians who want to discredit an opponent; they usually call it "flip-flopping" or "waffling" and use it to imply that the opponent can't make up their mind.
 * A german politican once said 'I don't care about the shit I said last week!'
 * A common version used against complaints is for a debater to bring up a separate event which they feel their opponent should have had the same reaction to; the "where were you when..." argument is always invalid. Whether the opponent should have been equally outraged at another event has no effect on whether their outrage at this event is valid.
 * A recent example of this was the controversy over Resident Evil 5's alleged racism. A common rebuttal was that those complaining about a white man shooting black people did not complain about the previous game where a white man was shooting Hispanic people, so a) their complaints were not valid, or b) shooting black people was somehow considered "worse" than shooting Hispanics.
 * Keynes's often-quoted response to such tactics:

"Healy: You're a fucking cheat. Atherton: When in Rome, dear boy..."
 * Used in an episode of Scrubs, when Eliot railed at the "hypocrisy" of Dr. Cox advising someone to calm down for the sake of his blood pressure, or Dr. Kelso telling a patient to stop smoking. When she herself got a patient who was fainting due to being slightly less underweight than she was, she initially tried to build her own weight in concert with the patient, but eventually realized "This is about you, not me."
 * "A strong leader is expected to maintain steadfast resolve in his opinion even if the environment changes or he gets new information. In any other context, that would be considered the first sign of a brain tumor." ~ Scott Adams
 * During an Australia vs England Cricket match, Mike Atherton edged the ball to wicketkeeper Ian Healy, but was given "not out", prompting the following exchange:


 * The ever-persistent "You criticize X, but you're using something provided by X!" argument.

Looks like this fallacy but is not

 * When it brings up a valid point about the speaker's reliability; for example, they are drunk or have previously been established to be a compulsive liar.
 * When the value of the speaker's word is being considered in order to evaluate his statements as testimony. It is not fallacious for a court to consider the reliability of a witness doubtful if they find he has a history of committing perjury or has accepted money in exchange for his testimony; it is only fallacious if his testimony is discarded out of hand on this basis, regardless of what it actually is.
 * When the speaker is arguing that the opponent is treating something as uniquely wrong, yet has done the same thing themselves. For example, if a boy is sent to his room for being the only person in his house to ever raid the biscuit tin, it would not be fallacious for him to point out that he did it because he saw his father doing it, therefore it is not valid to punish him on that basis.

Style Over Substance
Also called:
 * If You Can't Say Something Nice
 * Appeal To Brevity
 * Too long; Didn't read ( tl;dr or "teal deer")
 * Grammar Nazi

Another sub-type of Ad Hominem, the style over substance fallacy is where the manner in which an argument is presented is held to affect the validity of that argument.

A common version is to dismiss an entire argument if the person making it uses bad language or insults, or sounds "too angry"—in essence, claiming that since their opponent cannot conduct themselves "politely," they obviously have nothing worthwhile to add to the discussion. Throwing someone out for breaking rules of conduct is not fallacious, but throwing their arguments out on this basis certainly is.

Another common variant is to disregard an argument presented in an allegedly incorrect manner; for example, because it is too long, too short, badly-spelled, badly punctuated, or uses poor grammar. Not making the effort to make a coherent, concise reply is certainly rude, but as above, being rude is not the same as being wrong. This fallacy is quite common in internet discussions, and boils down to "You didn't present your argument the way I like, therefore it is wrong."

Note that saying "Your argument is presented poorly, therefore I will not read/ listen to it," is not a logical fallacy, unless you also state that the argument they were making is false because of its poor presentation.

Looks like this fallacy but is not

 * When the presentation is so unclear that it is genuinely impossible to follow the reasoning.
 * When the errors are pointed out simply for the sake of pointing out the errors, rather than as evidence that the arguer is wrong.
 * When the opponent is using a fallacious Proof by Verbosity; firing so many weak points off that it is impossible to respond to them within the format of the debate. In essence, the opponent may have nothing but mud to sell, but by piling it up so thick so quickly they hope to pass it off as rock solid. One example here, from Duane Gish. The Proof by Verbosity is an informal fallacy.
 * In court proceedings, it is normal for both parties to use ad hominem arguments against the persons the other party has called to present expert testimony. In this context, the tactic is valid because the judge and the jury, by virtue of not being experts in the field testimony is being provided on (for example, medical evidence), are not qualified to assess the matter on technical grounds and have to judge in virtue of whose authority they find more persuasive.

A good discussion of the ad hominem fallacy on the Internet may be found on the website of one Stephen Bond. See also You Fail Logic Forever and Hitler Ate Sugar.