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Common Logical Fallacies

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Presentation on theme: "Common Logical Fallacies"— Presentation transcript:

1 Common Logical Fallacies
Flawed Arguments

2 LOGICAL FALLACIES… Flaws in an argument Often subtle
Learning to recognize these will: Strengthen your own arguments Help you critique other’s arguments

3 Hasty Generalization A generalization based on insufficient or unrepresented evidence Deaths from drug overdoses in Metropolis have doubled over the last three years. Therefore, more Americans than ever are dying from drug abuse. One student is arrested for drugs and suddenly all students in that school are called druggies.

4 Non Sequitur (Does Not Follow)
A conclusion that does not follow logically from preceding statements. Or the train of thought jumps the tracks at some point. Mary loves children, so she will make an excellent school teacher. (This support alone does not follow or is Non-Sequitor—If Mary is a murderer, or has a 50 IQ, she will not make a good teacher no matter how much she loves kids.) No one should grill their steaks. Cows don’t like smoke. (This does not follow because it does not make sense. The cows are dead. They are steaks.)

5 False Analogy The assumption that because two things are alike in some respects, they are alike in others. If we put humans on the moon, we should be able to find a cure for the common cold! IF teachers can use the phones and drink coffee in school, students should be able to also! If adults can legally drink alcohol, teenagers should be able to also!

6 “EITHER… OR” FALLACY The suggestion that only two alternatives exist when in fact there are more. Either learn how to program a computer, or you won’t be able to get a decent job after college.

7 False Cause (Post Hoc, Coincidence vs. Causality)
The assumption that because one event follows another, the first is the cause of the second. Every time I wear my blue sweater, it snows. OMG, MY BLUE SWEATER CAUSES SNOW!!!

8 TU QUO QUE YOU DO IT TOO Saying they do it too does not negate their argument it is valid. Claiming a person’s argument is wrong or weak because they do the behavior they are arguing against. Ex: Dr. says “Stop smoking or you will die. You have bronchitis. Patient says “I don’t have to listen to you, you smoke too!”

9 Circular Reasoning/ Begging the Question
An argument in which the writer, instead of applying evidence simply restates the point in other language. God exists. How do you know? The Bible says so. Who wrote the Bible? God. Chicken nuggets are good. Why are they good? Because they are tasty. Why are they tasty? Because they are good!

10 FALSE AUTHORITY The person presenting the argument is an authority, but not on the subject at hand. Three types: Self Proof—”Because I said so” Spokes Person—”Because famous person says so” Too much Credit—”Because they are good at one thing, they know all things” I have a degree in Medicine and I am here to tell you the economy is about to FAIL!

Proving your argument through fear or the threat of consequences instead of using logical reasoning. Scare people in order to prove your point. “If you do not believe in God, you will go to Hell.” “Global warming will kill us all so stop using hairspray.” “If you do not sit down, I will fail you.”

An attack on the person proposing an argument rather than on the argument itself. Senator Jones was a conscientious objector during the Vietnam War, so his proposal to limit military spending has no merit. Why are you talking about an open campus? You cannot even drive, silly sophomore!

13 Red Herring An argument that focuses on an irrelevant issue to detract attention from the real issue. A Red Herring is literally a SMELLY FISH. You basically say, “My back is against the wall. I cannot win this argument. HERE IS AN AWFUL SMELLY FISH TO DISTRACT YOU! Mom, I know I have ISS for tardies but at least I am not doing drugs like all those other kids up there!

14 Pity (Ad Misericordiam)
Ad Misericordiam is an appeal to accept the truth of a conclusion out of pity for the arguer or some third party. Either the arguer (or someone else) is already an object of pity, or they will become one if the conclusion is not accepted. If I don’t get at least a B in this course my GPA will drop below If that happens I’ll lose my scholarship and have to quit school, so I ought to get a B in this course.

15 Non-Disproof One sometimes encounters arguments that some claim should be accepted because they have never been disproved. The move from ‘not disproved’ to ‘proved’ is invalid. No one has ever proven that I can’t flap my arms and fly, so maybe I can. No one has ever shown that it is impossible that the stars rule our lives; therefore, astrology is true. No one has ever proved that Big Foot doesn’t exist, so thus he does!

16 SLIPPERY SLOPE Like a muddy hill, if we go down this slope we will fall If we allow one thing a whole slew of other, negative events will occur as a result If we allow students to have ipods, pretty soon they will have entire systems out in class bumping bass all over the school. If we pass this health care bill eventually the government will take over the decision-making from patients and doctors

17 STRAW MAN The person attacks an argument which is different from, and usually weaker than, the opposition's best argument. Setting up a fake version of something or someone that is easy for others to not like. Ex. Katie, my shih-tzu, isn’t really hungry; she just wants us to get up all the time and cater to her every whim! People who think abortion should be banned have no respect for the rights of women. They treat them as nothing but baby-making machines. That's wrong. Women must have the right to choose.

18 Circular reasoning

19 Either/Or

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