13-Ling-21---Lecture-6---Logical-Fallacies-I.ppt

13-Ling-21---Lecture-6---Logical-Fallacies-I.ppt

• 1.
  Ling 21, Lecture6: Logical Fallacies - I
• 2.
  Two weeks ago,we studied about… • Various patterns of deductive arguments. – Modus ponens – Categorical syllogisms – Argument by elimination – Argument based on mathematics – Argument from definition – *Denying the antecedent – *Affirming the consequent *These are faulty patterns of deductive reasoning!
• 3.
  Two weeks ago,we also studied about • Various patterns of inductive arguments – Inductive generalization – Predictive argument – Argument from authority – Causal argument – Statistical argument – Argument from analogy
• 4.
  Finally, we alsostudied about … • Deductive validity and soundness • Inductive strength and cogency Deductive Inductive Valid Invalid Strong Weak (all are (all are unsound uncogent) Sound Unsound Cogent Uncogent
• 5.
  YOU MUST KNOWTHESE THINGS TO GET THROUGH THIS COURSE!!!
• 6.
  This week, wewill learn about … Logical Fallacies
• 7.
  What you shouldget from Ch. 5 • You should understand that a logical fallacy is an argument that contains a mistake of reasoning. Further, you should note that . . . • fallacies are divided into two broad categories: – Fallacies of relevance, and – Fallacies of insufficient evidence
• 8.
  Logical Fallacy • Alogical fallacy – or fallacy for short – is an argument that contains a mistake in reasoning. • Fallacies of relevance are mistakes in reasoning that occur because the premises are logically irrelevant to the conclusion. • Fallacies of insufficient evidence are mistakes in reasoning that occur because the premises, though logically relevant to the conclusion, fail to provide sufficient evidence to support the conclusion.
• 9.
  The Concept ofRelevance • A statement is relevant to another when it provides at least some evidence or reason for thinking that the second statement is true or false. • A statement can be either – Positively relevant – Negatively relevant – Logically irrelevant
• 10.
  Positive Relevance • Astatement is positively relevant to another statement if it counts in favor of that statement. – Labradors are dogs. Dogs are domestic animals, So Labradors are domestic animals. – Most SJSU students live off-campus. Annie is an SJSU student. So probably Annie lives off-campus. – Chris is a woman. Therefore, Chris enjoys knitting. • Each of the premises is positively relevant to the conclusion.
• 11.
  2 Important Pointsabout Relevance • A statement can be relevant to another statement even if the first statement is completely false. – Dogs are cats. Cats are felines. So dogs are felines. • Whether a statement is relevant to another usually depends on the context in which the statement is made. – A) All dogs have five legs. B) Rover is a dog. So C) Rover has five legs. – A is positively relevant to C only because of B
• 12.
  Negative Relevance • Astatement is negatively relevant to another if it counts against that statement. – Marty is a high- school senior. So Marty likely has a Ph.D. – Althea is two years old. So Althea probably goes to college.
• 13.
  Logical Irrelevance • Astatement is logically irrelevant to another statement if it counts neither for nor against that statement. – The earth revolves around the sun. Therefore, marijuana should be legalized. – Last night I dreamed that the Yankees will win the pennant. Therefore, the Yankees will win the pennant. Exercise 5.1, p. 121
• 14.
  Fallacies of Relevance •Occur when an arguer offers reasons that are logically irrelevant to his or her conclusion – Personal Attack (Ad Hominen) – Attacking the Motive – Look Who’s Talking (Tu Quoque, /tu kwoʊkwɛ/ ) – Two Wrongs Make a Right – Scare Tactics – Appeal to Pity – Bandwagon Argument – Straw Man – Red Herring – Equivocation – Begging the Question
• 15.
  Personal Attack (AdHominem) • Rejects someone’s argument or claim by attacking the person rather than the person’s argument or claim. a) X is a bad person. b) Therefore, X’s argument must be bad. Example: Hugh Hefner, founder of playboy magazine, has argued against censorship of pornography. But Hefner is an immature, self-indulgent millionaire who never outgrew the adolescent fantasies of his youth. His argument, therefore, is worthless. Hugh Hefner is a bad person. Therefore, Hugh Hefner’s argument must be bad.
• 16.
  Personal Attack (AdHominem) • The fallacy of personal attack occurs only if 1) An arguer rejects another person’s argument or claim, AND 2) The arguer attacks the person who offers the argument or claim, rather than considering the merits of that argument or claim.
• 17.
  Personal Attack (AdHominem) • Not all personal attacks are fallacies!!! – Millions of innocent people died in Stalin’s ruthless ideological purges. Clearly Stalin was one of the most brutal dictators of the twentieth century. – Ms Fibber has testified that she saw my client rob the Bank. But Ms Fibber has twice been convicted of perjury. In addition, you’ve heard her own mother testify that she is a pathological liar. Therefore, you should not believe Ms. Fibber’s testimony against my client. In these cases, the personal attacks are relevant to the conclusion so no fallacy is committed.
• 18.
  Attacking the Motive •An arguer criticizes a person’s motivation for offering a particular argument or claim, rather than examining the worth of the argument or claim itself. a) X is biased or has questionable motives. b) X’s argument or claim should be rejected. Examples: Professor Smith has argued in favor of academic tenure. But why should we even listen to him? As a tenured professor, of course he supports tenure. Senator Pork supports the stimulus package. Representing a state that will get a new bridge, of course he supports it.
• 19.
  BUT …. • ‘BurtonWexler, spokesperson for the American Tobacco Growers Association, has argued that there is no credible scientific evidence that cigarette smoking causes cancer. Given Wexler’s obvious bias in the matter, his arguments should be taken with a grain of salt.’ • This argument reflects a common sense assumption that the arguments put forward by Mr. Wexler need to be scrutinized with particular care. It is not a fallacy of attacking the motive.
• 20.
  Look Who’s Talking(Tu Quoque /tu kwoʊkwɛ/ ) • An arguer rejects another person’s argument or claim because that person fails to practice what he or she preaches. a) X fails to follow his or her own advice. b) Therefore, X’s claim or argument should be rejected. Examples: Doctor: You should quit smoking. Patient: Look who’s talking! I’ll quit when you quit. Parent: I don’t want you to smoke marajuana. Son: But you told me that you did when you were my age.
• 21.
  BUT …. • Jim:Our neighbor Joe gave me a hard time yesterday about washing my car during this drought emergency. Patti: Well, he’s right. But I wish that hypocrite would follow his own advice. Just last week I saw him watering his lawn in the middle of the afternoon. • Patti is not rejecting any argument by the neighbor, so no fallacy is committed.
• 22.
  Two Wrongs Makea Right • An arguer attempts to justify a wrongful act by claiming that some other act is just as bad or worse. a) Others are committing worse or equally bad acts. b) Therefore my wrongful act is justified. Examples: I don’t feel guilty about cheating on Dr. Boyer’s tests. Half the class cheats on his tests. Why pick on me, officer? Nobody comes to a complete stop at that stop sign. Mom: Kaia, stop hitting your sister. Kaia: Well, she pinched me.
• 23.
  BUT …. • Arethese cases of ‘2 Wrongs Make a Right?’ – Umpire: Why did you throw at the batter’s head? Pitcher: Because he threw at three of our players. I have an obligation to protect my teammates if you guys don’t. – Jeff Dahmer murdered seventeen men in cold blood. Therefore, Jeff Dahmer should be put to death. They commit the fallacy of ‘2WMR’ only if the justification is insufficient to warrant the apparent wrong-doing – debatable!
• 24.
  Scare Tactics • Anarguer threatens harm to the reader / listener and this threat is irrelevant to the truth of the arguer’s conclusion. – Diplomat to diplomat: I’m sure you’ll agree that we are the rightful rulers of the San Marcos Islands. It would be regrettable if we had to send armed forces to demonstrate the validity of our claim. – Gun lobbyist to politician: This gun-control bill is wrong for America, and any politician who supports it will discover how wrong they were at the next election.
• 25.
  BUT …. a) Parentto teen: If you come home late one more time, your allowance will be cut. b) President John Kennedy to Soviet Premier Nikita Krushchev: If you don’t remove your nuclear missiles from Cuba, we will have no choice but to remove them by force. If we use force to remove the missiles, that may provoke an all-out nuclear war. Neither of us wants a nuclear war. Therefore, you should remove your missiles from Cuba. (paraphrase) a) = statement, not an argument; b) = not a fallacy; premises are logically relevant to conclusion
• 26.
  Appeal to Pity •An arguer attempts to evoke feelings of pity or compassion, when such feelings are not logically relevant to the arguer’s conclusion. – Student to professor: I know I missed half your classes and failed all my exams, but I had a really tough semester. First my pet boa constrictor died. Then my girlfriend told me she wants a sex-change operation. With all I went through this semester, I don’t think I really deserved an F. Any chance you might cut me some slack and change my grade? – Parent to football coach: I admit that my son Billy can’t run, pass, kick, catch, block or tackle, but he deserved to make the football team. If he doesn’t make the team, he’s going to be an emotional wreck, and he may even drop out of school.
• 27.
  BUT …. • Whatabout these arguments? Mother to daughter: Nana was asking about you the other day. She’s so lonely and depressed since Grandpa passed away, and her Alzheimer’s seems to get worse every day. She’s done so much for you over the years. Don’t you think you should pay her a visit? High school softball coach: Girls, this state championship is the biggest game of your lives. This is what you’ve been working for all year. Your parents are counting on you, your school is counting on you, and your community is counting on you. Make them proud! Play like the champions you are! Here the emotional appeals are appropriate and relevant to the arguers’ purposes; hence no fallacy is committed.
• 28.
  Bandwagon Argument • Anargument plays on a person’s desire to be popular, accepted, or valued, rather than appealing to logically relevant reasons or evidence. a) Most (or a select group of) people believe or do X. b) Therefore, you should believe or do X. Examples: – All the really cool kids in your fraternity smoke cigarettes. Therefore, you should, too. – There must be something to astrology. Millions of Americans can’t be wrong.
• 29.
  BUT …. • Allthe villagers I’ve talked to say that the water is safe to drink. Therefore, the water probably is safe to drink. • Lots of my friends recommend the Back Street Deli, so it’s probably a good place to eat. • In these bandwagon appeals, the premises are relevant to the conclusion, so the arguments are not fallacious.
• 30.
  Straw Man • Anarguer distorts an opponent’s argument or claim in order to make it easier to attack A) X’s view is false or unjustified [but where X’s view has been unfairly characterized]. B) Therefore, X’s view should be rejected. • Examples: Pete has argued that the NY Yankees are a better baseball team than the Atlanta Braves. But the Braves aren’t a bad team. They have a great pitching staff, and they consistently finish at or near the top of their division, Obviously, Pete doesn’t know what he’s talking about. Senator Biddle has argued that we should outlaw violent pornography. Obviously the senator favors complete governmental censorship of books, magazines, and films. Frankly, I’m shocked that such a view should be expressed on the floor of the U.S. senate. It runs counter to everything this great nation stands for.
• 31.
  Red Herring • Anarguer tries to sidetrack his or her audience by raising an irrelevant issue and then claims that the original issue has effectively been settled by the irrelevant diversion. Examples: Many people criticize Thomas Jefferson for being an owner of slaves. But Jefferson was one of our greatest presidents, and his Declaration of Independence is one of the most eloquent pleas for freedom and democracy ever written. Clearly these criticisms are unwarranted. Critics have accused my administration of doing to little to save the family farm. These critics forget that I grew up on a farm. I know what it’s like to get up at the crack of dawn to milk the cows. I know what it’s like to work in the field all day in the blazing sun. Family farms are what made this country great, and those who criticize my farm policies simply don’t know what they’re talking about.
• 32.
  BUT …. Political opponent:Congressman Crookley, now that you have been convicted of bribery, extortion, and grand theft auto, isn’t it high time that you resigned from office? Rep. Crookley: How ‘bout those Yankees? A ten- game lead at the All-Star break! Simply changing or evading the subject without denying the charge or pretending to refute it is not a fallacy.
• 33.
  Equivocation • A keyword is used in two or more senses in the same argument and the apparent success of the argument depends on the shift in meaning. – Any law can be repealed by the proper legal authority. The law of gravity is a law. Therefore, the law of gravity can be repealed by the proper legal authority. When the two senses of ‘law’ (laws regulating human conduct vs. uniformities of nature) are made explicit, it is apparent that the premises don’t support the conclusion, hence a fallacious argument!
• 34.
  Begging the Question •An arguer states or assumes as a premise the very thing he or she is trying to prove as a conclusion. • Two common ways to beg the question – Restating the conclusion in slightly different words. Capital punishment is morally wrong because it is ethically impermissible to inflict death as punishment for a crime. – Circular reasoning B: God wrote the bible. N: How do you know? B: Because it says so in the Bible and what the Bible says is true. N: How to you know what the Bible says is true? B: Because God wrote the Bible.
• 35.
  Let’s practice recognizingsome of these fallacies!
• 36.
  According to thesong, the pinball wizard is deaf, dumb, and blind. Dumb people aren't very smart. So, the pinball wizard isn't very smart. Based on your reading of this chapter, what fallacy does this argument commit?
• 37.
  According to thesong, the pinball wizard is deaf, dumb, and blind. Dumb people aren't very smart. So, the pinball wizard isn't very smart. The fallacy of equivocation. The arguer uses the word "dumb" in two different senses. In the first sentence, "dumb" means "unable to speak." In the second sentence, it means "unintelligent." Consequently, although the argument may superficially appear to be valid, the premises do not support the conclusion.
• 38.
  I'm trying hardto understand this guy who identifies himself as a security supervisor and criticizes the police officers in this area. I can only come up with two solutions. One, he is either a member of the criminal element, or two, he is a frustrated security guard who can never make it as a police officer and figures he can take cheap shots at cops through the newspaper. (adapted from a newspaper call-in column) Based on your reading of this chapter, what fallacy does this caller commit?
• 39.
  I'm trying hardto understand this guy who identifies himself as a security supervisor and criticizes the police officers in this area. I can only come up with two solutions. One, he is either a member of the criminal element, or two, he is a frustrated security guard who can never make it as a police officer and figures he can take cheap shots at cops through the newspaper. (adapted from a newspaper call-in column) The fallacy of personal attack. The caller never responds to the previous caller's arguments. Instead, he simply attacks his or her character. By criticizing the previous caller's motives, the arguer also commits the fallacy of attacking the motive.
• 40.
  The Red Crossis worried about the treatment of the suspected terrorists held by the U.S. at Guantanamo Bay, Cuba. What do they want the U.S. to do with them, put them on the beaches of Florida for a vacation or take them skiing in the Rockies? Come on, let's worry about the Americans. (adapted from a newspaper call-in column) Based on your reading of this chapter, what fallacy does this argument commit?
• 41.
  The Red Crossis worried about the treatment of the suspected terrorists held by the U.S. at Guantanamo Bay, Cuba. What do they want the U.S. to do with them, put them on the beaches of Florida for a vacation or take them skiing in the Rockies? Come on, let's worry about the Americans. (adapted from a newspaper call-in column) The fallacy of straw man. The Red Cross, of course, is not suggesting that the detainees be treated as vacationers. The caller is misrepresenting the Red Cross's argument in order to make it appear ridiculous.
• 42.
  Barbara Youngblood, amember of the Wilkes-Barre (Pa.) School Board for twenty-three years, had six relatives on the school district payroll before she was voted out of office in 2003. When questioned, she offered the following justification for nepotism in public education: "Every board member is pushing somebody for a job -- friends' kids, neighbors' kids. . . . This happens not only in the School District. People have relatives working in the same company. It's an everyday happening. Is that a sin?" (Wilkes-Barre Times Leader, November 17, 2002) Based on your reading of this chapter, what fallacy does Youngblood commit?
• 43.
  Barbara Youngblood, amember of the Wilkes-Barre (Pa.) School Board for twenty-three years, had six relatives on the school district payroll before she was voted out of office in 2003. When questioned, she offered the following justification for nepotism in public education: "Every board member is pushing somebody for a job -- friends' kids, neighbors' kids. . . . This happens not only in the School District. People have relatives working in the same company. It's an everyday happening. Is that a sin?" (Wilkes-Barre Times Leader, November 17, 2002) Bandwagon argument. The speaker attempts to justify nepotism--a practice that creates clear conflicts of interest and often results in the hiring of less- qualified applicants--simply by noting that it is widely practiced.
• 44.
  Paul: My philosophyteacher said that it's impossible to prove that our memories are sometimes reliable. It's just something we have to take on faith. Lisa: That's baloney. I can remember countless times when I recalled information correctly. Isn't that proof enough? Based on your reading of this chapter, what fallacy does Lisa commit?
• 45.
  Paul: My philosophyteacher said that it's impossible to prove that our memories are sometimes reliable. It's just something we have to take on faith. Lisa: That's baloney. I can remember countless times when I recalled information correctly. Isn't that proof enough? X Begging the question. Lisa is trying to prove that our memories are sometimes reliable. Yet in saying that she remembers times when her memory was accurate, she is assuming what she attempts to prove.