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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The Seven Deadly Logical Sins
Ways to use logic as a shieldSlide2
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
Elephants are animals.
You are an animal.
That makes you an elephant.Slide4
“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
—repeating the same thing as if I am proving something.
“All logical fallacies come down to bad logic.”Slide6
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?
“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
—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
The Black & White Fallacy—5:50
The Authority Fallacy—7:40
The No-True-Scotsman Fallacy—9:30Slide10
Spot the Fallacies
The Fallacy Fallacy--https://www.youtube.com/watch?v=oGBO-WMrlIQ&index=2&list=PLtHP6qx8VF7dPql3ll1To4i6vEIPt0kV5Slide11
First Deadly Sin: The False Comparison
“Made with all natural ingredients.”
…all natural… or …all-natural…
Purple is not a fruit!
all natural fallacy
assumes that members of the same family assume the same traits.Slide14
appeal to popularity
legitimizes your choice by claiming that others have chosen it.Slide15
—reducing an argument to absurdity.
(The premise is unbelievable.)Slide16
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.”Slide17
Candidate: I’m a successful business man. Elect me and I will run a successful city.Slide18
--mistaking one kind of unit for another.
(Keep track of the difference between a piece of the pie and the whole pie.)Slide20
Read the discussion about the cost of detergent (143-144). (unit fallacy)Slide21
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.)Slide22
Proper Rhetorical Reply: Good! That’ll keep a couple more potential criminals off the streets.Slide23
offers too few examples to prove the point.
Coworker: That intern from Yale was great. Let’s get another
Proper Rhetorical Reply: Didn’t that jerk in Legal go to Yale?Slide24
Third Deadly Sin: Ignorance as Proof
The 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.
There’s nothing wrong with you. The lab tests came back negative.Slide25
Proof: The lab tests are all negative. So…
Conclusion: Nothing is wrong with you.Slide26
Fourth Deadly Sin: The Tautology
basically just repeats the premise.
Fan: The Cowboys are favored to win since they’re the better team.Slide27
It is also called “
begging the question
“You can trust our candidate because he is an honest man.”Slide28
The Fifth Deadly Sin: The False Choice
: Two or more issues get squashed into one, so that a conclusion proves another conclusion.
The “when did you stop beating your wife” ploy.Slide29
—you are given two choices when you actually have many choices.
<The cat fancier discussion, Pg. 147 – 148>Slide30
fallacy—Only one cause gets the blame (or credit) for something that has many causes.
<The faulty motorcycle helmet>Slide31
The Sixth Deadly Sin: The Red Herring
(the Chewbacca defense)—Switches issues in mid-argument to throw the audience off the sent.Slide32
tactic—a version of the red herring fallacy; it switches topics to one that is easier to fight.Slide33
The Seventh Deadly Sin: The Wrong Ending
—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.Slide34
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 absurdumSlide35
post hoc ergo propter hoc
fallacy (the chanticleer fallacy)—after this, therefore because of this.Slide36
“Our newsletter is a big success. After we started publishing it, alumni giving went up.”