bassham3 powerpoint lecturenotes_ch05

Lecture Notes © 2008 McGraw Hill Higher Education© 2008 McGraw Hill Higher Education

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Critical ThinkingChapter 5

Logical Fallacies I

Fallacies of Relevance


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Definitions Logical Fallacy (or fallacy): an argument that contains a mistake in

reasoning. Fallacy of Relevance: mistakes in reasoning that occur because the

premise are logically irrelevant to the conclusion. Relevance: A statement is relevant to another statement if it would, if

true, provide at least some evidence that the second statement is true or false. Notice that relevance has nothing to do with truth. A can be relevant to B,

even if A (and/or B) is false. Argument that commits a fallacy of relevance is an argument whose

premises provide no evidence that the conclusion is true. Don’t confuse it with an argument that commits a fallacy of insufficient

evidence. Such an argument provides some but not enough evidence for its conclusion.


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Types of Relevance Positive Relevance: X has positive relevance

to Y, if X provides evidence that Y is true. Example: All dogs have five legs and rover is a

dog. So Rover has five legs. Negative Relevance: X has negative relevance

to Y, if X provides evidence that Y is false. Example: Marty is a high-school senior. So Marty

likely has a Ph.D.


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Fallacies of Relevance Personal Attack (ad Hominem) Attacking the Motive Look Who’s Talking (Tu Quoque) Two Wrongs Make a Right Scare Tactics Appeal to Pity Bandwagon Argument Straw Man Red Herring Equivocation Begging the Question


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Personal Attack (Ad Hominem) This is the fallacy that dismisses an argument by attacking

the person that made the argument, rather than attacking the claims themselves.

e.g., Hugh Hefner argued against censorship. But Hugh Hefner is a degenerate. Therefore, his argument is worthless.

Common pattern:1. X is a bad person2. Therefore, X’s argument must be faulty.

Personal attacks are not fallacious when they appear in arguments that are trying to establish something about the character of the person.

Stalin killed millions; therefore Stalin was ruthless. Becky is a pathological liar; therefore her testimony is not good

evidence.


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Attacking the Motive …the error of criticizing a person’s motivation for offering a

particular argument or claim. e.g., Prof Michelson has argued in favor of tenure. But of course he

does, he is a tenured professor. The fact that someone would benefit from a conclusion’s truth, does not

entail that their argument doesn’t establish the truth of that conclusion. Common pattern:

1. X is biased or has questionable motives2. Therefore, X’s argument or claim should be rejected.

However, motivation is not always irrelevant. If someone is motivated to misrepresent the facts, then you have a good reason to be skeptical about the “facts” they put forth.

e.g., Bob said that there is no scientific evidence that smoking can cause cancer. But Bob is a spokesperson for the tobacco corporations, so you shouldn't believe that there is no such evidence just because he says there isn’t.


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Look Who’s Talking (Tu Quoque) …when an arguer rejects another person’s argument or claim

because that person fails to “practice what they preach.” e.g., I don’t need to stop smoking just because my doctor tells me to; he

smokes and won’t stop either! Common pattern:

1. X fails to follow his/her own advice.2. Therefore, X’s claim or argument should be rejected.

Arguments are good or bad because of their own intrinsic strengths or weaknesses, not because of who offers them up.

If an argument is good, it is good no matter who articulates it. But hypocritical behavior can (and should) be criticized.

e.g., I should stop smoking like my doctor told me; but so should my doctor!


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Two Wrongs Make a Right This fallacy is committed when one tries to make a

wrong action look right, by comparing it to another wrong (perhaps worse) action. e.g., I don’t feel guilty about cheating; everyone does it.

Common forms: X is common behavior; therefore, X is not wrong. X is worse than Y. Therefore Y is not wrong.

However, sometimes actions can be justified by the fact that other action have taken place. e.g., I killed the man because he was about to kill me; it was

an act of self-defense.


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Scare Tactics This fallacy is committed when an arguer threatens harm

(physical or non-physical) to a reader or listener if he or she does not accept the argument's conclusion and this threat is irrelevant to the truth of the conclusion.

e.g., This gun control bill is wrong for America, and any politician who supports it will discover how wrong s/he is at the next election.

Common form:1. If you accept what I say something bad will happen. 2. Therefore, what I say is true.

Such arguments are not always fallacious. If the natural consequences of doing X are negative, then the consequences of doing X are relevant to the truth of the statement “You should not do X.”

e.g., You shouldn’t pass that law, it will hurt the public welfare.


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Appeal to Pity …occurs when an arguer inappropriately attempts to

evoke feelings of pity or compassion from his listeners or readers. e.g., He deserves to start on the football team; if he doesn’t

he will be really upset. A starting position is deserved by ability, not by reaction.

e.g., You shouldn’t give me an F in the class just because I failed all the exams; I had really rough semester. A grade is deserved by achievement, not by circumstance.

Such arguments are not always fallacious. If feelings are a legitimatize motivating factor for action, then brining out those feelings are appropriate to persuade. e.g., Everyone is counting on you; you should play hard!


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Bandwagon Argument ...an argument that plays on a person’s desire to

be popular, accepted, or valued. e.g., Everyone who is cool smokes. So you should

too. Common form:

1. Everyone believes (or does) X.2. Therefore, you should believe (or do) X too.

Such arguments are not always fallacious. e.g., All the villagers say it is safe to drink the

water, so it is probably safe to drink.


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Straw Man …fallacy is committed when an arguer distorts an

opponent’s argument to make it weak (like a straw man) and thus easier to attack.

e.g., Bob argued that we should outlaw violent pornography. Obviously he is against free-speech. No one should take him seriously.

This “re-casts” the plausible “anti-violent pornography” argument as not-so-plausible “anti free-speech” argument.

Common pattern:1. Misrepresentation of X’s view. 2. That view is false. 3. Therefore X’s view should be rejected.


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Red Herring …is committed when an arguer tries to sidetrack his audience by

raising an irrelevant issue and then claims that the original issue has effectively been settled by the irrelevant diversion. e.g., Many people criticize Jefferson for owning slaves. But he was one of

our greatest presidents. Such criticisms must be unfounded. Such arguments are not always fallacious. Sometimes people

raise irrelevant issues—not to try to fool people into thinking that the original issue has been solved—but to avoid addressing the original issue at all. Q: Aren’t you guilty? A: How about them Yankees!

Since such arguments don’t attempt to settle the original argument, they are not “Red Herrings.”


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Equivocation An arguments commits the fallacy of equivocation

when it “switches the meaning” of one or more of its ambiguous terms.

e.g., (1) Any law can be repealed. (2) So the law of gravity must be able to be repealed.

The meaning of “law” is different in (1) than it is in (2). The fallacy becomes apparent when we clarify the

meaning of word “law” in each statement. (1) All rules regulating human behavior can be repealed.

(2) So the observed uniformity of all things being pulled toward the earth by gravity can be repealed.


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Begging the Question …is committed when one assumes, as a premise, the

very thing that is one’s conclusion. e.g., Capital punishment is wrong because it is ethically

impermissible to inflict death as punishment for a crime. The conclusion is just a restatement of the premise.

Example: 1. Everything The Bible says is true2. The Bible says that whatever it says is true. 3. Therefore, whatever The Bible says is true.

Common form: P. Therefore P.

Hint: If it is impossible to accept one of the premises unless you already accept the conclusion, then the argument begs the question.