The Seven Deadly Logical Sins Ways to use logic as a shield Spot Fallacies Homer Lisa would you like a doughnut Lisa No thanks Do you have any fruit Homer This has purple in it Purple is a fruit ID: 621246
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Spot Fallacies
The Seven Deadly Logical Sins
Ways to use logic as a shieldSlide2
Spot Fallacies
Homer: Lisa, would you like a doughnut?
Lisa: No, thanks. Do you have any fruit?Homer: This has purple in it. Purple is a fruit.Slide3
Spot Fallacies
Elephants are animals.
You are an animal.That makes you an elephant.Slide4
Spot Fallacies
“All logical fallacies come down to…bad logic. In the logic of deliberative argument, you have the proof and a choice. // It starts with what the audience knows or believes—the commonplace—and applies it to a particular situation to prove your conclusion. In deduction, the commonplace serves as your proof. The proof in induction is a set of examples.”Slide5
Spot Fallacies
Tautology—repeating the same thing as if I am proving something.“All logical fallacies come down to bad logic.”Slide6
Spot Fallacies
Does a fallacy lie hidden in an argument?
Does the proof hold up?Am I given the right number of choices?
Does the proof lead to the conclusion?
Who cares?Slide7
Spot Fallacies
“In rhetoric, on the other hand, there are really no rules. You can commit fallacies to your heart’s content, so long as you get away with them. Your audience bears the responsibility to spot them; but if it dies, there goes your ethos.”Slide8
Spot Fallacies
Bad Proofs
—include three sins: false comparison (lumping examples of the wrong category), bad example, and ignorance as proof (asserting that the lack of examples proves something.)Wrong number of choices—covers one essential sin, the false choice: offering just two choices when more are available, or merging two or three issues into one.
Disconnect between proof and conclusion—results in the tautology (in which the proof and the conclusion are identical), the red herring (a sneaky distraction), or the wrong ending (in which the proof fails to lead to the conclusion).Slide9
Spot the Fallacies
https://www.youtube.com/watch?v=8qb-h0sXkH4
Strawman—1:50Ad Hominem—3:45Ad Homiem Tu quoque—4:39The Black & White Fallacy—5:50The Authority Fallacy—7:40The No-True-Scotsman Fallacy—9:30Slide10
Spot Fallacies
The
appeal to popularity legitimizes your choice by claiming that others have chosen it.It might be against the law to drink when you are 18 years old, but everyone does it, so it's okay.Slide11
Spot Fallacies
Reductio ad absurdum—reducing an argument to absurdity.You are in trouble for skipping school, but you tell your father, "All of my friends were going!"He says, "Well, if all of your friends were going to jump off of a bridge, would you do that, too?"Slide12
Spot Fallacies
The
fallacy of antecedent…Driver: I don’t have to slow down. I haven’t had an accident yet.
(It never happened before, so it never will. / It’s happened before, so it will happen again.)
“My dog doesn’t bite.”Slide13
Spot Fallacies
The false analogy…Candidate: I’m a successful business man. Elect me and I will run a successful city.
People who cannot go without their coffee every morning are no better than alcoholics.Slide14
Spot Fallacies
Second Deadly Sin: The Bad Example
Misinterpreting the evidence—
Parent: Seeing all those crimes on TV makes me want to lock up my kids and never let them out.
(Evidence doesn’t support the conclusion.)Slide15
Spot Fallacies
Proper Rhetorical Reply: Good! That’ll keep a couple more potential criminals off the streets.Slide16
Spot Fallacies
The
hasty generalization offers too few examples to prove the point.Coworker: That intern from Yale was great. Let’s get another Yalie.
Proper Rhetorical Reply: Didn’t that jerk in Legal go to Yale?Slide17
Spot Fallacies
Third Deadly Sin: Ignorance as ProofThe fallacy of ignorance—If we can’t prove it, then it must not exist. Or, if we can’t disprove it, then it must exist.
Doctor: There’s nothing wrong with you. The lab tests came back negative.Slide18
Spot Fallacies
Proof: The lab tests are all negative. So…
Conclusion: Nothing is wrong with you.Slide19
Spot Fallacies
Fourth Deadly Sin: The TautologyThe tautology basically just repeats the premise.
Fan: The Cowboys are favored to win since they’re the better team.Slide20
Spot Fallacies
It is also called “
begging the question”.
“You can trust our candidate because he is an honest man.”Slide21
Spot Fallacies
The Fifth Deadly Sin: The False ChoiceMany Questions: Two or more issues get squashed into one, so that a conclusion proves another conclusion.
The “when did you stop beating your wife” ploy.Slide22
Spot Fallacies
The
complex cause fallacy—Only one cause gets the blame (or credit) for something that has many causes.
<The faulty motorcycle helmet>Slide23
Spot Fallacies
The Sixth Deadly Sin: The Red HerringThe red herring (the Chewbacca defense)—Switches issues in mid-argument to throw the audience off the sent.
In government, arguing for raising taxes - “We need more revenue to support the programs that we have. Children are our future. Let’s support children.”Slide24
Spot Fallacies
The
straw man tactic—a version of the red herring fallacy; it switches topics to one that is easier to fight.Senator Smith says that the nation should not add to the defense budget. Senator Jones says that he cannot believe that Senator Smith wants to leave the nation defenseless.
Caroline says that she thinks her friends should not be so rude to the new girl. Jenna says that she cannot believe that Caroline is choosing to be better friends with the new girl than the girls who have always known her.Slide25
Spot Fallacies
The Seventh Deadly Sin: The Wrong EndingThe slippery slope—if we allow this reasonable thing, it will inevitably lead to an extreme version of it.
Parent: If I let you skip dinner, then I’ll have to let the other kids skip dinner.Slide26
Spot Fallacies
Mixing up cause and effect—“Budget cuts are ruining our children!”The best argument against the slippery slope is concession. The slippery slope has a built-in reduction ad absurdumSlide27
Spot Fallacies
The
post hoc ergo propter hoc fallacy (the chanticleer fallacy)—after this, therefore because of this.
The temperature has dropped this morning, and I also have a headache. The cold weather must be causing my headache.Slide28
Spot Fallacies
“Our newsletter is a big success. After we started publishing it, alumni giving went up.”