LOGICAL FALLACIES

Informal Reasoning

A

fallacy is a failure in

reasoning that leads to an

argument being invalid.

T

hey are like cracks in the

foundation of a building;; if

they are present, the building

is going to fall down.

FALLACY

WHY SHOULD WE LEARN FALLACIES?

D

etecting fallacies is a very important part of making

yourself critically skilled.

I

f you know what fallacies are, you can…• Avoid making them yourself when you present

an argument.• Spot them when others are using them.

WHO USES FALLACIES?

E

veryone… at times.

S

ome are present innocently.

S

ome are done deliberately.• Advertising• Politics• Media• Law

1. Hasty generalization

2. Post hoc ergo

propter hoc

3. Ad hominem fallacy

4. Circular reasoning

5. Special pleading

10 LOGICAL FALLACIES

6. Equivocation

7. Argument ad

ignorantiam

8. False analogy

9. False dilemma

10.Loaded questions

HASTY GENERALIZATION

Generalizing from not enough

evidence

Stereotyping• Example: He’s Mexican so he

must know how to garden.

POST HOC ERGO PROPTER HOC

A

n immediate jump to a conclusion without enough or

very little evidence.

S

omething is not the cause of something else just

because they follow each other.• Example: People who drink one glass of wine a

day have a lower chance of heart disease.

AD HOMINEM FALLACY

R

ejecting what someone says solely on the basis of

whom they are or what they believe.

A

ttacking or critiquing the person instead of critiquing

the argument or point made.• Example: President Wilson supported the

League of Nations so it must be a good thing.

CIRCULAR REASONING

V

icious circle: One negative action/idea or wrong way

of thinking leads to another.

J

ust assuming something is true when you are supposed

to be proving it.• I know that Sandra is innocent because Sandra

would not lie to me.

SPECIAL PLEADING

J

ust because you are in a crisis, you believe that you

deserve “the second chance”.

H

aving “Double Standards”… Do as I say, not as I do.• Example: The city has asked residents to conserve

water, everyone is expected to limit things such as showers but you make an exception for yourself… after all you hair is long and thick.

EQUIVOCATION

A term used in two or more senses with a single argument.

C

omparing two like things that are not really alike or

language is ambiguous or unclear.• Example: A hamburger is better than nothing;

nothing is better than good health; therefore, a hamburger is good health.

ARGUMENT AD IGNORANTIAM

T

o claim that something is true on the grounds

that there is no evidence to dispute it.• Example: I believe zombies exist because

no one can prove they don’t.• Example: I believe God exists because no

one can prove that he doesn’t.

FALSE ANALOGY

J

ust because two things are similar in some

situations does not mean they are in all

situations.• Example: Just as in time the gentle rain

can wear down the tallest mountains, so, in human life, all problems can be solved by patience and quiet persistence.

FALSE DILEMMA

A

ssuming only two black and white dilemmas exist or divide

things into two types.

W

hen you leave little option or only two options- when in reality,

things are rarely so simple.• Example: Do people who want to see an increase in

military spending really want to see our schools close? (This makes it sound like tax money either goes entirely to military or entirely to education.)

LOADED QUESTION

T

o put an assumption in a question.

A

question with a false, disputed, or question-begging

presupposition.• Example: Do you always cheat on tests?

• It is assuming that you have cheated on tests at some point in time.