Math 101

Logic ExercisesProfessor Richard Blecksmithrichard@math.niu.edu

Dept. of Mathematical SciencesNorthern Illinois University

Math 101 Website:http://math.niu.edu/∼richard/Math101Section 2 Website:http://math.niu.edu/∼richard/Math101/fall06

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Informal Fallacy ExercisesI. Identify the fallacy of relevance in the followingpassages.

Explain your answer.

(Sometimes more than one fallacy is involved.)

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Informal Fallacy ExercisesI. Identify the fallacy of relevance in the followingpassages.

Explain your answer.

(Sometimes more than one fallacy is involved.)

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Informal Fallacy ExercisesI. Identify the fallacy of relevance in the followingpassages.

Explain your answer.

(Sometimes more than one fallacy is involved.)

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Fallacy Number 11. You can’t believe what Professor MarsHead saysabout the importance of higher salaries for teachers.As a teacher himself, he would naturally be in favor ofincreasing teachers’ pay.

Circumstantial

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Fallacy Number 11. You can’t believe what Professor MarsHead saysabout the importance of higher salaries for teachers.As a teacher himself, he would naturally be in favor ofincreasing teachers’ pay.

Circumstantial

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Fallacy Number 33. The wives of successful men wear expensiveclothing. So the best way for a woman to help herhusband become a success is to buy expensiveclothing.

False Cause

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Fallacy Number 33. The wives of successful men wear expensiveclothing. So the best way for a woman to help herhusband become a success is to buy expensiveclothing.

False Cause

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Fallacy Number 55. Our team is the outstanding team in the conference,because it has the best players and the best coach. Weknow it has the best players and the best coachbecause it will win the conference title. And it willwin the conference title because it deserves to win, forit is the outstanding team in the conference.

Begs Question

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Fallacy Number 55. Our team is the outstanding team in the conference,because it has the best players and the best coach. Weknow it has the best players and the best coachbecause it will win the conference title. And it willwin the conference title because it deserves to win, forit is the outstanding team in the conference.

Begs Question

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Fallacy Number 66. Mr. Scrooge, my husband certainly deserves a raisein pay. I can hardly manage to feed the children onwhat you have been paying him. And our youngestchild, Tiny Tim, needs an operation if he is ever towalk without crutches.

Appeal to Pity

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Fallacy Number 66. Mr. Scrooge, my husband certainly deserves a raisein pay. I can hardly manage to feed the children onwhat you have been paying him. And our youngestchild, Tiny Tim, needs an operation if he is ever towalk without crutches.

Appeal to Pity

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Fallacy Number 77. Our tests have shown that the drug in question hasno medicinal value whatever, certainly none for theailments it is claimed to cure. We conclude, therefore,that it cannot be sold successfully and will be acommercial failure.

Irrelevant Conclusion

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Fallacy Number 77. Our tests have shown that the drug in question hasno medicinal value whatever, certainly none for theailments it is claimed to cure. We conclude, therefore,that it cannot be sold successfully and will be acommercial failure.

Irrelevant Conclusion

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Fallacy Number 88. During the war enemy espionage rings wereexposed by tapping the telephone wires of suspects.Therefore the authorities should have the telephonewires of all suspicious persons tapped.

Hasty Generalization

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Fallacy Number 88. During the war enemy espionage rings wereexposed by tapping the telephone wires of suspects.Therefore the authorities should have the telephonewires of all suspicious persons tapped.

Hasty Generalization

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Fallacy Number 99. It matters very little now what the King of Englandeither says or does; he hath wickedly broken throughevery moral and human obligation, trampled natureand conscience beneath his feet, and by a steady andconstitutional spirit of insolence and cruelty procuredfor himself universal hatred. – Thomas Paine

Abusive

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Fallacy Number 99. It matters very little now what the King of Englandeither says or does; he hath wickedly broken throughevery moral and human obligation, trampled natureand conscience beneath his feet, and by a steady andconstitutional spirit of insolence and cruelty procuredfor himself universal hatred. – Thomas Paine

Abusive

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Fallacy Number 1010. No breath of scandal has ever touched the Senator.Therefore he must be incorruptibly honest.

Ignorance

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Fallacy Number 1010. No breath of scandal has ever touched the Senator.Therefore he must be incorruptibly honest.

Ignorance

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Fallacy Number 1111. In that melancholy book The Future of anIllusion, Dr. Freud himself one of the last greattheorists of the European capitalist class, has statedwith simple clarity the impossibility of religious belieffor the educated man of today. – John Strachey

False Authority

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Fallacy Number 1111. In that melancholy book The Future of anIllusion, Dr. Freud himself one of the last greattheorists of the European capitalist class, has statedwith simple clarity the impossibility of religious belieffor the educated man of today. – John Strachey

False Authority

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Fallacy Number 1212. The Inquisition must have been justified andbeneficial, if whole people invoked and defended it, ifmen of the loftiest souls founded and created itseverally and impartially, and its very adversariesapplied it on their own account, pyre answering topyre. – Benedetto Croce

Appeal to the People

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Fallacy Number 1212. The Inquisition must have been justified andbeneficial, if whole people invoked and defended it, ifmen of the loftiest souls founded and created itseverally and impartially, and its very adversariesapplied it on their own account, pyre answering topyre. – Benedetto Croce

Appeal to the People

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Fallacy Number 1313. It is too my turn to pitch today. After all, it’s myball!

Appeal to Force

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Fallacy Number 1313. It is too my turn to pitch today. After all, it’s myball!

Appeal to Force

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Fallacy Number 1515. Of course socialism is desirable. Look at the facts.At one time all utilities were privately owned, nowmore and more of them are owned by the government.The social security laws embody many of theprinciples that socialists have always maintained. Weare well on our way to socialism, and its completetriumph is inevitable.

Irrelevant Conclusion and Hasty Generalization

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Fallacy Number 1515. Of course socialism is desirable. Look at the facts.At one time all utilities were privately owned, nowmore and more of them are owned by the government.The social security laws embody many of theprinciples that socialists have always maintained. Weare well on our way to socialism, and its completetriumph is inevitable.

Irrelevant Conclusion and Hasty Generalization

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Fallacy Number 1818. The Golden Rule is basic to every system of ethicsever devised, and everyone accepts it in some form orother. It is, therefore, an undeniably sound moralprinciple.

Appeal to the People

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Fallacy Number 1818. The Golden Rule is basic to every system of ethicsever devised, and everyone accepts it in some form orother. It is, therefore, an undeniably sound moralprinciple.

Appeal to the People

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Fallacy Number 2121. Are you in favor of increased governmentalservice and higher taxes?

Complex Question

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Fallacy Number 2121. Are you in favor of increased governmentalservice and higher taxes?

Complex Question

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Fallacy Number 2222. Of course there is a Santa Claus. But he doesn’tbring any presents to children who do not believe inhim.

Begs Question and Force

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Fallacy Number 2222. Of course there is a Santa Claus. But he doesn’tbring any presents to children who do not believe inhim.

Begs Question and Force

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Fallacy Number 2323. The alarmists have not succeeded in proving thatradioactive fallout is dangerously harmful to humanlife. Therefore it is perfectly safe to continue ourprogram of testing nuclear weapons.

Ignorance

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Fallacy Number 2323. The alarmists have not succeeded in proving thatradioactive fallout is dangerously harmful to humanlife. Therefore it is perfectly safe to continue ourprogram of testing nuclear weapons.

Ignorance

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Fallacy Number 2727. My doctor has some nerve telling me to loseweight. After all, he weighs more than I do.

Circumstances

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Fallacy Number 2727. My doctor has some nerve telling me to loseweight. After all, he weighs more than I do.

Circumstances

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Fallacy Number 2828. In his work an attorney is free to consult lawbooks. And a physician often looks up cases in hermedical texts. Everyone should be allowed a similarfreedom of reference. So students should be permittedto use their textbooks during exams.

Accident

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Fallacy Number 2828. In his work an attorney is free to consult lawbooks. And a physician often looks up cases in hermedical texts. Everyone should be allowed a similarfreedom of reference. So students should be permittedto use their textbooks during exams.

Accident

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Fallacy Number 2929. While General Grant was winning battles in theWest, President Lincoln received many complaintsabout Grant’s being a drunkard. When a delegationtold him one day that Grant was hopelessly addictedto whiskey, the President is said to have replied: “Iwish General Grant would send a barrel of hiswhiskey to each of my other generals!”

False Cause

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Fallacy Number 2929. While General Grant was winning battles in theWest, President Lincoln received many complaintsabout Grant’s being a drunkard. When a delegationtold him one day that Grant was hopelessly addictedto whiskey, the President is said to have replied: “Iwish General Grant would send a barrel of hiswhiskey to each of my other generals!”

False Cause

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Fallacy Number 3030. The story is told about Wendell Phillips, theabolitionist. One day he found himself on the sametrain with a group of Southern clergymen. When theSoutherners learned of Phillips’ presence, theydecided to have some fun at his expense. One of themapproached and asked “Are you Wendell Phillips?”“Yes, sir,” came the reply.“Are you the great abolitionist?”“I am not great, but I am an abolitionist.”“Are you not the one who makes speeches in Bostonand New York against slavery?”“Yes, I am.”“Why don’t you go to Kentucky and make yourspeeches there?”

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Fallacy Number 30 Cont’dPhillips looked at his questioner for a moment and

then asked, “Are you a clergyman?”“Yes, I am.”“Are you trying to save souls from hell?”“Yes.”“Well—why don’t you go there?”

Abusive

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Fallacy Number 30 Cont’dPhillips looked at his questioner for a moment and

then asked, “Are you a clergyman?”“Yes, I am.”“Are you trying to save souls from hell?”“Yes.”“Well—why don’t you go there?”

Abusive

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Fallacies of AmbiguityII. Identify the fallacy of ambiguity in the followingpassages.

Explain your answer.

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Fallacies of AmbiguityII. Identify the fallacy of ambiguity in the followingpassages.

Explain your answer.

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Fallacy Number 3131. To press forward with a properly ordered wagestructure in each industry is the first condition forcurbing competitive bargaining. But there is no reasonwhy the process should stop there. What is good foreach industry can hardly be bad for the economy as awhole.

composition

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Fallacy Number 3131. To press forward with a properly ordered wagestructure in each industry is the first condition forcurbing competitive bargaining. But there is no reasonwhy the process should stop there. What is good foreach industry can hardly be bad for the economy as awhole.

composition

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Fallacy Number 3333. Traffic accidents are increasing. Collisionsbetween Model T Fords are traffic accidents.Therefore collisions between Model T Fords areincreasing.

division

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Fallacy Number 3333. Traffic accidents are increasing. Collisionsbetween Model T Fords are traffic accidents.Therefore collisions between Model T Fords areincreasing.

division

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Fallacy Number 3535. Her father had a very distinguished appearance, sohe must be a very distinguished man.

equivocation

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Fallacy Number 3535. Her father had a very distinguished appearance, sohe must be a very distinguished man.

equivocation

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Fallacy Number 3636. Psychology testing established that Mr. Jones’concern with money was above average and that Mrs.Jones’ concern with money was below average. Itfollows that Jones likes money more than his wife.Their marriage is not likely to last, for how can a manstand a woman to whom he prefers money?

grammar

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Fallacy Number 3636. Psychology testing established that Mr. Jones’concern with money was above average and that Mrs.Jones’ concern with money was below average. Itfollows that Jones likes money more than his wife.Their marriage is not likely to last, for how can a manstand a woman to whom he prefers money?

grammar

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Fallacy Number 3737. Each manufacturer is perfectly free to set the priceon the product he or she produces, so there can benothing wrong with all manufacturers getting togetherto fix the prices of the articles made by all of them.

composition

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Fallacy Number 3737. Each manufacturer is perfectly free to set the priceon the product he or she produces, so there can benothing wrong with all manufacturers getting togetherto fix the prices of the articles made by all of them.

composition

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Both TypesIII. Identify the informal fallacy in the followingpassages.

Both fallacies of relevance and ambiguity are mixedtogether.

Explain your answer.

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Both TypesIII. Identify the informal fallacy in the followingpassages.

Both fallacies of relevance and ambiguity are mixedtogether.

Explain your answer.

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Both TypesIII. Identify the informal fallacy in the followingpassages.

Both fallacies of relevance and ambiguity are mixedtogether.

Explain your answer.

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Fallacy Number 4040. The army is notoriously inefficient, so we cannotexpect Private Pyle to do an efficient job.

division

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Fallacy Number 4040. The army is notoriously inefficient, so we cannotexpect Private Pyle to do an efficient job.

division

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Fallacy Number 4141. It is necessary to confine criminals and to lock uplunatics. Therefore there is nothing wrong withdepriving people of their liberties.

accident or hasty generalization

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Fallacy Number 4141. It is necessary to confine criminals and to lock uplunatics. Therefore there is nothing wrong withdepriving people of their liberties.

accident or hasty generalization

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Fallacy Number 4343. Congress shouldn’t bother to consult the JointChiefs–of–Staff about military appropriations. Asmembers of the armed forces, they will naturally wantas much money for military purposes as they thinkthey can get.

circumstances

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Fallacy Number 4343. Congress shouldn’t bother to consult the JointChiefs–of–Staff about military appropriations. Asmembers of the armed forces, they will naturally wantas much money for military purposes as they thinkthey can get.

circumstances

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Fallacy Number 4545. Narcotics are habit–forming. Therefore if youallow a doctor to ease your pain with codeine, youwill become a hopeless drug addict.

accident

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Fallacy Number 4545. Narcotics are habit–forming. Therefore if youallow a doctor to ease your pain with codeine, youwill become a hopeless drug addict.

accident

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Fallacy Number 4646. Officer: You can’t park here. I don’t care what thesign says. If you don’t move, I’ll give you a ticket!

force

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Fallacy Number 4646. Officer: You can’t park here. I don’t care what thesign says. If you don’t move, I’ll give you a ticket!

force

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Fallacy Number 5151. Telemarketer: Now that I have explained ourhealth insurance plan, all I need is to verify youraddress in order to mail the membership papers toyou.

complex question

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Fallacy Number 5151. Telemarketer: Now that I have explained ourhealth insurance plan, all I need is to verify youraddress in order to mail the membership papers toyou.

complex question

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Fallacy Number 5252. There’s no point in hiring a skilled worker to dothe job, because many who are regarded as skilledworkers are no more skilled than anybody else.

Irrelevant Conclusion

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Fallacy Number 5252. There’s no point in hiring a skilled worker to dothe job, because many who are regarded as skilledworkers are no more skilled than anybody else.

Irrelevant Conclusion

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Fallacy Number 5454. Lawyer: My client is the sole support of his agedparents. If he is sent to prison it will beak their hearts,and they will be left homeless and penniless. Yousurely cannot find it in your hearts to reach any otherverdict that “not guilty.”

pity

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Fallacy Number 5454. Lawyer: My client is the sole support of his agedparents. If he is sent to prison it will beak their hearts,and they will be left homeless and penniless. Yousurely cannot find it in your hearts to reach any otherverdict that “not guilty.”

pity

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Fallacy Number 5555. Was it through stupidity or through deliberatedishonesty that the Administration has hopelesslybotched its foreign policy?

complex question

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Fallacy Number 5555. Was it through stupidity or through deliberatedishonesty that the Administration has hopelesslybotched its foreign policy?

complex question

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Fallacy Number 5757. “The NFL, NHL, and NBA, with their arrogance,addictions, and passions have become a hideouspastime. . . Never mind that todays pros, once iconsand, dare we say, role models, have becomephilistines, thugs, addicts, and worst of all, whiners.Simpering, petulant, enough–is–never–enoughwhiners.”

abusive

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Fallacy Number 5757. “The NFL, NHL, and NBA, with their arrogance,addictions, and passions have become a hideouspastime. . . Never mind that todays pros, once iconsand, dare we say, role models, have becomephilistines, thugs, addicts, and worst of all, whiners.Simpering, petulant, enough–is–never–enoughwhiners.”

abusive

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Fallacy Number 5858. “It isn’t the high price of stars that is expensive,it’s the high price of mediocrity.” – Bill Veeck

equivocation

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Fallacy Number 5858. “It isn’t the high price of stars that is expensive,it’s the high price of mediocrity.” – Bill Veeck

equivocation

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Fallacy Number 5959. Boy: I’ll be good if you give me a dollar.Mother: Why can’t you be like your father? He’sgood for nothing.

grammatical construction

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Fallacy Number 5959. Boy: I’ll be good if you give me a dollar.Mother: Why can’t you be like your father? He’sgood for nothing.

grammatical construction

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PROJECT 2Due: In recitation the week after Thanksgiving

Find two real-life examples of informal fallacies.Examine various sources such as the Chicago Tribune,the DeKalb Daily Chronicle, the Northern Star,Newsweek, Time, or television. If the example is inprint, cut it out and include it in your essay. A Xeroxcopy will do. Identify each fallacy made and explainhow the example involves that fallacy. Is the argumentconvincing or appealing?

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PROJECT 2Due: In recitation the week after Thanksgiving

Find two real-life examples of informal fallacies.Examine various sources such as the Chicago Tribune,the DeKalb Daily Chronicle, the Northern Star,Newsweek, Time, or television. If the example is inprint, cut it out and include it in your essay. A Xeroxcopy will do. Identify each fallacy made and explainhow the example involves that fallacy. Is the argumentconvincing or appealing?

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Homework, Recitation, Test 3• No recitation next week

• No homework is due• Solutions to the Informal Fallacy Exercises are

posted on–line• Exam 3 is Monday, Nov 20

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Homework, Recitation, Test 3• No recitation next week• No homework is due

• Solutions to the Informal Fallacy Exercises areposted on–line

• Exam 3 is Monday, Nov 20

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Homework, Recitation, Test 3• No recitation next week• No homework is due• Solutions to the Informal Fallacy Exercises are

posted on–line

• Exam 3 is Monday, Nov 20

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Homework, Recitation, Test 3• No recitation next week• No homework is due• Solutions to the Informal Fallacy Exercises are

posted on–line• Exam 3 is Monday, Nov 20

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Miniquiz 101 pt What’s your name, Z-number, and RecitationSection Number?

Find validity rule (if the argument is valid):Where there’s smoke, there’s fire.There is no fire in the basement.Therefore, there is no smoke in the basement.

(a) direct reasoning(b) indirect reasoning(c) transitivity(d) the or rule(e) invalid

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Miniquiz 101 pt What’s your name, Z-number, and RecitationSection Number?

Find validity rule (if the argument is valid):Where there’s smoke, there’s fire.There is no fire in the basement.Therefore, there is no smoke in the basement.

(a) direct reasoning(b) indirect reasoning(c) transitivity(d) the or rule(e) invalid

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