COMMON LOGICAL FALLACIESFlawed Arguments

WHAT IS FALLACY? Fallacies are defects that weaken arguments.

First, fallacious arguments are very, very common and can be quite persuasive, at least to the casual reader or listener. You can find dozens of examples of fallacious reasoning in newspapers, advertisements, and other sources.

Second, it is sometimes hard to evaluate whether an argument is fallacious.

An argument might be very weak, somewhat weak, somewhat strong, or very strong. An argument that has several stages or parts might have some strong sections and some weak ones.

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.

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-Sequitur—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.)

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!

“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.

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!!!

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!

FALSE AUTHORITYThe person presenting the argument is an

authority, but not on the subject at hand.

Three types:1. Self Proof—”Because I said so”2. Spokesperson—”Because famous person says

so”3. 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!

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!

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 2.0. If that happens I’ll lose my scholarship and have to quit school, so I ought to get a B in this course.

SLIPPERY SLOPE Like a muddy hill, if we go down this slope we will

fall If we allow one thing, 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

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.

CAN YOU NAME THIS FALLACY?

1) It is ridiculous to have spent thousands of dollars to rescue those two whales trapped in the Arctic ice. Why look at all the people trapped in jobs they don’t like.

RED HERRING

CAN YOU NAME THIS FALLACY?

2) Plagiarism is deceitful because it is dishonest.

BEGGING THE QUESTION

CAN YOU NAME THIS FALLACY?

3) Water fluoridation affects the brain. Citywide, student’s test scores began to drop five months after fluoridation began.

POST HOC (false cause)

CAN YOU NAME THIS FALLACY?

4) I know three redheads who have terrible tempers, and since Annabel has red hair, I’ll bet she has a terrible temper too.

HASTY GENERALIZATION

CAN YOU NAME THIS FALLACY?

5) You support capital punishment just because you want an “eye for an eye,” but I have several good reasons to believe that capital punishment is fundamentally wrong…

STRAW MAN

CAN YOU NAME THIS FALLACY?

6) We have to stop the tuition increase! The next thing you know, they'll be charging $40,000 a semester!

SLIPPERY SLOPE