Changing the subject fallacies
Changing the subject fallacies change the subject by discussing the person making the argument instead of discussing reasons to believe or disbelieve the conclusion. While sometimes it may be useful to cite authorities, it is almost never appropriate to discuss the person instead of the argument.
Argumentum ad Hominem
Argumentum ad hominem literally means "argument directed at the man." The person presenting an argument is attacked instead of the argument itself. For example, the person's character, nationality or religion may be attacked, or, it may be pointed out that a person stands to gain from a favorable outcome, or, a person may be attacked by association or by the company he or she keeps. There are three major forms of Attacking the Person:
- ad hominem (abusive): is the abusive form where a person refuses to accept a statement, and justifies the refusal by criticizing the person who made the statement.
"You claim that taekwondo is effective on the street but yet you have been seriously injured during street attacks."
This is a fallacy because the truth of an assertion does not depend on the virtues of the person asserting it. A less blatant form of this fallacy is to reject a proposition based on the fact that it was also asserted by some other easily criticized person. For example:
"So you think the best way to teach a class is to run the class in a military manner. I am sure the Hitler and Stalin would have agreed with you."
- ad hominem (circumstantial): instead of attacking an assertion, the author points to the relationship between the person making the assertion and the person's circumstances. For example:
"You must not stress physical fitness in your style of Karate, since you are obviously obese."
- ad hominem (tu quoque): this form of attack on the person notes that a person does not practice what he or she preaches. You may also allege that someone is rationalizing a conclusion for selfish reasons, is also known as "poisoning the well." It is not always invalid to refer to the circumstances of an individual who is making a claim. If someone is a known liar, that fact will reduce his or her credibility. However, this may not prove that he or she is lying in a particular statement. Also, being a liar does not alter the soundness of any logical arguments that the person may make. For example:
"Of course you believe that there is no discrimination in taekwondo schools. You are white."
"You say I shouldn't drink, but you haven't been sober for more than a year."
Argumentum ad Verecundiam (Appeal to Authority)
While sometimes it may be appropriate to cite an authority to support a point, often it is not. In particular, an appeal to authority is inappropriate if:
The person is not qualified to have an expert opinion on the subject, such as a celebrity. For example:
"Shirley McLain is a great actress, and she believes in psychics."
Experts in the field disagree on this issue. For Example:
"Economist John Kenneth Galbraith argues that a tight money policy is the best cure for a recession." (Although Galbraith is an expert, not all economists agree on this point.)
The authority was making a joke, drunk, or otherwise not being serious. For example:
"We are headed for nuclear war. Last week Ronald Reagan remarked that we begin bombing Russia in five minutes." (Of course, he said it as a joke during a microphone test.)
A variation of the fallacious appeal to authority is hearsay. An argument from hearsay is an argument which depends on second or third hand sources. For example:
"My friend heard on the news the other day that Canada will declare war on Serbia. (This is a case of hearsay; in fact, the reporter said that Canada would not declare war.)
This appeal to authority argument is not always invalid. It may be relevant to refer to a widely-regarded authority in a particular field, if you are discussing that field. For example: we can distinguish quite clearly between:
"Phillip Porter thinks that chokes are an effective self-defense tactic."
and
"Sugar Ray Leonard thinks that board breaking serves no useful purpose."
Porter is a 10th degree black belt in Judo, so we can reasonably expect his opinions on choking to be informed. Leonard is a boxer, so it is questionable whether he is qualified enough to speak on the subject of board breaking.
Anonymous Authorities
The authority in question is not named. This is a type of appeal to authority because when an authority is not named it is impossible to confirm that the authority is an expert. However, the fallacy is so common it deserves special mention. A variation on this fallacy is the appeal to rumor. Because the source of a rumor is typically not known, it is not possible to determine whether to believe the rumor. Very often false and harmful rumors are deliberately started to discredit an opponent. For example:
"Self-defense experts agree that traditional martial arts are useless on the streets."
"Rumor has it that Bruce Less died of a drug overdose"
Style Over Substance
The manner in which an argument (or arguer) is presented is taken to affect the likelihood that the conclusion is true. While it is true that the manner in which an argument is presented will affect whether people believe that its conclusion is true, nonetheless, the truth of the conclusion does not depend on the manner in which the argument is presented. For example:
"Nixon lost the presidential debate because of the sweat on his forehead."
"The instructor is overweight and out of shape. I wouldn't believe what he says about the martial arts."
