introduction and activities - ibdp theory of...

Logical Fallacies Introduction and Activities

What is a logical fallacy?

• A fallacy is an error of reasoning. These are flawed statements that often sound true

• The word “fallacy” may derive from the Latin word fallere meaning, “to deceive, to trip, to lead into error or to trick.”

• The word may also derive from the Greek phelos, meaning “deceitful.”

www.sun-design.com/talitha/fallacies.htm

Why study logical fallacies?

• It is important to develop logical fallacy detection skills in your own writing, as well as others’.

Think of this as “intellectual kung-fu: the art of intellectual self defense.” (Logical Fallacies Handlist)

Post hoc ergo propter hoc(Non sequitur )

Assuming one thing causes another just because one follows another.

• As the number of churches

in the USA increases, so do

the number of prostitutes

“Theory of Knowledge for the IB Diploma”, Richard van de Lagemaat, Cambridge University Press

•Crime is increasing in Germany, but so is the number of

college graduates. So education is corrupting the young

•The homeless man was seen in front of the shop before

it was robbed, so he did it

http://www.tbray.org/ongoing/When/200x/2006/03/17/-big/IMGP2990.jpg

Ad hominem • Attacking the person you disagree with instead of their

argument


•

As Hitler's interest in art attests, the love of art is a

dangerous antecedent to fascism

•You may argue that God doesn’t exist, but that’s just

because you are so bigoted.

•You claim that Tim is innocent, but why should we listen

to you? You are criminal too

Equivocation

This fallacy uses a word/idea with two different

meanings in two different ways to support an

argument

•Fries and a coke are better than nothing, and nothing is

better than good health, so fries and coke are better than

good health

•Scientists say that red wine can prevent heart disease. I

drink a bottle every night, so I must have a really healthy

heart.

Ad ignorantiam Claiming that something is true because it

cannot be proved to be false. “Theory of Knowledge for the IB Diploma”, Richard van de Lagemaat, Cambridge University Press

•You cannot explain where God is, so God doesn’t exist

•Scientist have not proven that global warming will

occur, so let’s not worry about it

False dilemma This fallacy presents a limited choice as the only

possible options when there may be many other choices/conclusions.

Assuming that only a limited number of alternatives exist.

Binary thinking-black/white thinking.


•If you don’t let me go to this party, I’ll be a total loser at school

•If you are against the war in Iraq, then you must hate America.

•Either we cut welfare benefits or we raise income tax : that is the

choice we face

Loaded question

A question that is biased because it contains a built-in assumption.


•Do you always cheat on exams? •Did you beat your students today? •Why do you hate America and freedom so much?

Hasty generalisation

Generalising from insufficient evidence.

• Fred the Australian stole my wallet. All Australian are thieves.

• Six of my friends like the new school uniform-it will be really popular

• All the new - born babies I’ve seen are so cute ! Our child is going to be absolutely adorable!


Special pleading Using double standards to excuse an

individual or group. “Theory of Knowledge for the IB Diploma”, Richard van de Lagemaat, Cambridge University Press

• The law requires everyone to follow the speed limit and other traffic regulations, but in Mumbai, exceptions should be made for cops and their families, police union officials say.

• I know there is a drought and we need to save water, but I am putting my prize flowers in a competition next week and I need to given them plenty of water

False analogy Assuming that

because two things are alike in one way that they are alike in other respects.

“Theory of Knowledge for the IB Diploma”, Richard

van de Lagemaat, Cambridge University Press

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

Circular reasoning Assuming the truth of what you are supposed

to be proving.


•The soldier gave out the guns, but kept an extra one for

himself. When asked why, he said “I am the leader”. Why

are you the leader? “Because I have more guns”

•I know my president is a good man, because he says he

is and a good man would not lie

•I know I am smarter than you, because it would be foolish

to say so if it wasn’t true, and I am not a fool.

Circular reasoning is the best fallacy and is

capable of proving anything. Since it can prove anything, it can obviously prove the above statement. Since it can prove the first statement, it must be

true. Therefore, circular reasoning is the best fallacy and is capable of proving anything.

In each of the following cases, decide which best applies to the argument.

Hasty generalisation, post hoc ergo propter hoc, circular reasoning, ad hominem, special pleading, ad ignorantium, false dilemma, false analogy, equivocation, loaded question.

1.

Since strict gun control laws were introduced in Dodge City, the crime rate has risen. This shows that gun control does nothing to reduce crime.


Hasty generalisation, post

hoc ergo propter hoc, circular

reasoning, ad hominem,

special pleading, ad

ignorantium, false dilemma,

false analogy, equivocation,

loaded question.

post hoc ergo propter hoc

Since strict gun control laws were introduced in Dodge City, the crime rate has risen. This shows that gun control does nothing to reduce crime.

2.

Emmeline said she trusted me, and she must be telling the truth because she wouldn’t lie to someone that she trusted.








loaded question.

circular reasoning

Emmeline said she trusted me, and she must be telling the truth because she wouldn’t lie to someone that she trusted.


3.

The ends justifies the means. After all, if you want to make omelettes, you have to break eggs.








loaded question.

false analogy

The ends justifies the means. After all, if you want to make omelettes, you have to break eggs.

4.

That can’t be right, non of my friends would believe it.








loaded question.

ad hominem

That can’t be right, non of my friends would believe it.

5.

Since many great scientists have believed in God, there must be some truth in religion.








loaded question.

ad hominem

Since many great scientists have believed in God, there must be some truth in religion.

6.

Teddy and Seanne got on very well on their two dates together. They are clearly well suited and should get married.








loaded question.

hasty generalisation

Teddy and Seanne got on very well on their two dates together. They are clearly well suited and should get married.

7.

Do you want to be part of the solution, or part of the problem?







loaded question.


false dilemma

Do you want to be part of the solution, or part of the problem?

8.

“I agree that you shouldn’t copy mp3s illegally, but I’ve only copied a few and I do buy tracks sometimes.”








loaded question.

special pleading

“I agree that you shouldn’t copy mp3s illegally, but I’ve only copied a few and I do buy tracks sometimes.”

9.

The average UK family has 2.5 children. The Smiths are average people, they must have 2.5 kids.








loaded question.

equivocation

The average UK family has 2.5 children. The Smiths are average people, they must have 2.5 kids.

10.

Since no-one has been able to prove that God didn’t create the universe, we must conclude that God did make everything.








loaded question.

ad ignorantium

Since no-one has been able to prove that God didn’t create the universe, we must conclude that God did make everything.

11.

Are all your family stupid, or is it just you?








loaded question.

loaded question

Are all your family stupid, or is it just you?

12.

No scandal has ever touched Mr Porter. He must be a clean living and honest man.








loaded question.

ad ignorantium

No scandal has ever touched Mr Porter. He must be a clean living and honest man.

13.

Just as you are more likely to take care of a car that you own rather than a car that you rent, a slave owner would look after a slave better than an employer would look after their worker.








loaded question.

false analogy

Just as you are more likely to take care of a car that you own rather than a car that you rent, a slave owner would look after a slave better than an employer would look after their worker.

14.

To ignore the possibility that Norway landed the first person on the moon just because nobody has heard of a Norwegian space program is arrogant. If we are unaware of something does not mean that it never happened.








loaded question.

ad ignorantium

To ignore the possibility that Norway landed the first person on the moon just because nobody has heard of a Norwegian space program is arrogant. If we are unaware of something does not mean that it never happened.

15.

In the fight against terrorism, you are either with the USA or against.








loaded question.

false dilemma

In the fight against terrorism, you are either with the USA or against.

Activity - “sell” a product

• Work on group • using as many fallacies as you can • go overboard to make the fallacies as

outrageous as possible. • After each group presents, the other class

members should try to identify the fallacies. • Cleaning products or products that invoke ideals

(like patriotism, environmentalism, corruption) work particularly well for this activity.

Causes of bad reasoning

• Rationalisation – Manufacturing arguments to justify our ignorance, pride, laziness and prejudices

• Take any editorial or opinion article from a newspaper and see how many logical fallacies you can find in it.

• Have you ever rationalized?

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