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“”If the facts are against you, argue the law. If the law is against you, argue the facts. If both the facts and the law are against you, abuse the other side's attorney.
The phrase ad hominem argument (often called an ad hominem attack) comes from the Latin "to the person." It also sometimes applies to any argument that centres on emotive (specifically irrelevant emotions) rather than rational or logical appeal.
As most people use the phrase in recent times, an ad hominem argument occurs when one attacks the person making an argument rather than the argument itself. It is therefore a special case of the broader category of formal logical fallacies, the non sequitur, in which the conclusion urged, e.g. that the disputant is incorrect, does not follow from the premise asserted, e.g. that the disputant is a dick. Even if the ad hominem attack is true, e.g. the disputant really is a dick, that fact has no bearing on whether the disputant's argument is logically sound.
The traditional meaning of the phrase is that an "argumentum ad hominem" is one tailored to appeal to the person with whom one is arguing rather than to impartial reason. This definition may be seen in Modern English Usage by H. H. Fowler, a book whose explanations of usage are often taken as highly authoritative, if not definitive. For example, if you wanted to convince someone that Costa Rica was a superior place to go on vacation and you knew that the person was a keen birdwatcher, you might point out that Costa Rica is full of interesting bird life.
Fowler also mentions the following types of argumenta:
... ad crumenam (purse), one touching the hearer's pocket
... ad baculum (stick) or baculimum, threat of force instead of argument;
... ad ignorantium, one depending for its effect on the hearer's not knowing something essential;
... ad populum, one pandering to popular passion;
... ad vericundiam (modesty), one to meet which requires the opponent to offend against decorum.
 How ad hominem works
Ad hominem arguments work via the halo effect, a 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 all good or tending to all bad. Thus, if you can attribute a bad trait to your opponent, others will tend to doubt the quality of your opponent's arguments.
 Strict usage
An ad hominem argument has the basic form:
- A makes claim X
- There is something objectionable about A
- Therefore X is false
 Subtle uses
Often, ad hominem attacks are used subtly in order to influence the views of spectators. There are many forms of this, such as pointing out bad things they (the opponent) have done in the past in arguments about morality (they are not attacking the person's points about morality, they are attacking the person), or using exclamations (for example, "Jeez!") to imply that the person is incredibly slow at understanding your point. While ad hominem attacks are used mostly in arguments about philosophy or morals, it can also be used in other debates, such as when people supporting evolution are said to be "justifying genocide and mass suicide," though this could also be referred to as a straw man fallacy.
 Blatant uses
Ad hominem attacks are hardly ever used plainly, and people who do are generally trolls who want to provoke people to fight. These are often partnered with not even responding to the person's post, using arguments that make no sense, and thus have never been heard of, then mocking their opponent when they fail to find a rebuttal, and many other such techniques.
 False positives
Ad hominem attacks are strictly fallacious when the attack has little or no bearing on the argument at hand, for example, dismissing a female scientist's opinion on a subject because she is a woman would be a fallacious ad hominem argument - dismissing it on grounds of insufficient qualification or experience would not be, although it may fall into other fallacious categories and may constitute a Courtier's Reply. Similarly, pointing out someone's known track record on a subject would also not count. For instance, YouTube creationist VenomFangX has a past history of filing false DMCA claims, and it would not be an ad hominem attack to bring this up should he file another. It would be an ad hominem however, if it was brought up to refute one of his YEC claims.
Calling someone an idiot when you have explained the evidence five times and they still refuse to address it, or provide counterexamples, is not an ad hominem attack, but rather a valid logical conclusion based on their actions. Similarly, tacking an insult onto the end of any argument might be bad form, but it doesn't automatically make it an ad hominem. It's only an ad hominem if you say the other person must be wrong because they are an idiot - not the other way round. Creationists sometimes make the mistake of calling a personal insult an ad hominem attack when it is not intended to address the truth or falsity of the creationist's claim, but merely to denigrate the creationist. Likewise, creationists are known to mischaracterize logically sound arguments as ad hominem attacks in an attempt to obscure the soundness of the argument or their burden to respond by making an emotional appeal.
A criticism is also not an ad hominem argument if a person's merits are actually the topic of the argument. A habitual liar is not physically incapable of telling the truth, and therefore dismissing their claims entirely is not valid, but it is certainly not incorrect to weigh their testimony as less trustworthy than that of someone with a reputation for studious honesty if comparing contradictory claims by the two.
 Test yourself
Because of the frequent misuse of ad hom as an accusation, here's a little test for the reader:
- "Of course she's wrong, girls can't do maths!"
- "Sorry, but you're just butt ugly and have a small penis."
- "Did you just escape from a mental hospital or something?"
- "I just don't trust people who dress like that, they should take pride in their appearance and not go around ungroomed if they want to be taken seriously!"
- "The Senator's past voting record of flip-flopping on the war makes him untrustworthy, so his evidence in this corruption hearing should be dismissed."
- "Consider the accused's heavy build and fondness for weightlifting, it's entirely plausible that he overwhelmed his attacker."
- "Why should we listen to you? You're Hitler!"
- "What you're doing there, is what's called an ad hominem attack!"
 See also
- Ad hoc
- Argumentum ad cellarium
- Argumentum ex culo
- Emotional appeal
- Non sequitur
- Red herring
- Shill gambit
- Mike Bara
- ↑ Thus it is permissible to infer that ad hominem argumentation should be generally understood as a confession that the disputant has nothing more substantive to offer, a long-winded version of a shrug and a "I got nothing."
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