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Informal Fallacies 1

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Page 1: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

Informal Fallacies1

Page 2: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

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Formal Vs Informal Fallacies

A fallacy is a defect in an argument other than its having false premises.

It refers to a defect that is difficult to be detected.

An informal fallacy is a defect in the content of an argument.

A formal fallacy is a defect in the structure of an argument.

Page 3: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

Formal fallacies can be understood as a use of invalid structures that look like valid structures in the first appearance.

E.g.: P Q / Q // P P Q / ~P // ~Q P v Q / P // ~Q

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Page 4: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

Informal Fallacies4

There are 5 main types of informal fallacies, comprising a total of 21 cases.

A. Fallacies of Irrelevance

B. Fallacies of Insufficiency

C. Fallacies of Inappropriate Assumption

D. Fallacies of Ambiguity

E. Fallacies of Grammatical Analogy

Page 5: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

THE PREMISES ARE PSYCHOLOGICALLY RELEVANT, BUT NOT LOGICALLY

RELEVANT, TO THE CONCLUSION.

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Fallacies of Irrelevance

Page 6: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

1. Appeal to Force6

Argumentum ad baculumThe arguer uses threat instead of evidence to

force the listener to accept the conclusion.

ExampleStudent: I deserve an A in the course. You know that my father is a good friend of the College Principal.

Page 7: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

2. Appeal to Pity7

Argumentum ad misericordiumThe arguer tries to win support by evoking

pity from the listener.

Page 8: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

3. Appeal to People8

Argumentum ad populumDirect approach - the arguer excites emotions

from the crowd. Indirect approach - the arguer appeals to

some individuals by focusing on some aspects of those individuals’ relationship to the crowd.

Page 9: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

Direct Approach9

Most of the political rhetoric uses the direct approach to arouse your favorable impression or resentment.

ExampleDescribe CY Leung as a “wolf.”Label national education as “brainwashing

education.”

Page 10: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

3 Types of Indirect Approach10

A. Bandwagon argumentThe arguer attempts to persuade the listener

by appealing to group pressure.

ExampleMany students choose this course.

Therefore, you should also take it.

Page 11: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

3 Types of Indirect Approach11

B. Appeal to vanityAppeal to the pride or conceit of the listener

in order to get them to do something.

ExampleOnly fools believe what CY Leung says.

Page 12: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

3 Types of Indirect Approach12

C. Appeal to snobberyAppeal to desire of the listener of being in a

particular social class.

ExampleOnly the selected few can own a platinum

card.

Page 13: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

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Page 14: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

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Page 15: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

4. Argument against the Person15

Argumentum ad hominemThe arguer attacks the opponent’s character

instead of his/her argument.

3 types of ad hominemBackground attackCircumstance attackYou too

Page 16: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

Background Attach16

A. Abuse your opponent based on her background.

ExampleCY Leung’s words should not be taken because he is a communist.

Page 17: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

Circumstance attack17

B. Present your opponent as predisposed to say or act in a certain way because of her circumstance.

ExampleAll the policies of CY Leung aim to protect the interests of Mainland because he tries to win the trust of the Central Government.

Page 18: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

You too18

C. Argue that doing something is right because your opponent is also doing the same thing.

ExampleTeacher: You should not skip class.

Student: I don’t think you haven’t skipped one.

Page 19: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

5 – Fallacy of Accident19

Misapply a general rule to a particular case because the particular case is an exceptional case (accident) beyond the scope of the rule.

ExampleExceeding the speed limit is illegal. Ambulance drivers always exceed the speed limit during emergency. Thus, their action is illegal.

Page 20: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

6. Straw Man20

During a debate between two sides, one side distorts its opponent's view (usually as a strengthened position) and then attacks the distorted argument.

ExampleA: The society should not discriminate gays.

B: So you are saying the everyone should be homosexual. It’s ridiculous!

Page 21: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

Example21

When one side argues that “Some X are Y”, this view can easily be distorted as “All X are Y”.

ExampleA: Smoking is bad to health. One of 10

smokers’ deaths is caused by diseases related to smoking.

B: That cannot be true. My grandfather has smoked since he was 16 and he is still very healthy.

Page 22: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

7. Fallacy of Missing the Point22

Ignoratio elenchiThis happens when the premises of an

argument lead, or seem to lead, to one conclusion but then a completely different conclusion is drawn.ExampleMany welfare receivers are new immigrants.Therefore, we should reduce drastically the number of immigrants.

Page 23: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

8. Red Herring23

During a debate, one side defends his position by stating a seemingly related but in fact irrelevant statement in order to change the subject of discussion.

The truth value of the new statement implies nothing about the truth value of the original position.

If the new statement is used to support the original position, the arguer is just missing the point.

Page 24: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

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E.g.:Animal rights activists say that animals are abused in biomedical research labs. But consider this: Pets are abused by their owners every day. Some cases of abuse are enough to make you sick.

Page 25: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

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A debate may be diverted into a discussion of the personal characteristics of the arguers

Consequently, the arguers will also commit the fallacy of attacking against the person.

E.g.:

A: You should not lie.B: But why are you so lazy?

Page 26: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

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An arguer may fasten on a trivial point in an opponent's argument, defeating him on that, and then leaving it to be supposed that he has been defeated on the main question.

E.g.:A: The Philippine President should apologize to the

families of the killed hostages. Ten people were killed due to the impotence of his government.

B: No, you get it wrong. There were eight, not ten, people were killed.

Page 27: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

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An arguer may begin a discussion by stating an extreme position (e.g., All X are Y) and then, when it is attacked, they replace for it a more moderate argument (Some X are Y).

E.g.: A: All the people getting social security

assistance are the new immigrants. B: Statistics shows that the majority of those who

receive the assistance are single families and seniors.

A: But you cannot deny that many of the new immigrants are receiving the assistance.

Page 28: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

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In order to argue that some evil should be tolerated, an arguer may point to some other evil that is worse than the first evil.

E.g:

A: You should quit smoking. B: You had better ask those drug addicts to

stop taking drugs.

Page 29: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

THE PREMISES ARE NOT STRONG ENOUGH TO JUSTIFY THE CONCLUSION.

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Fallacies of Insufficiency

Page 30: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

9. Appeal to Unqualified Authority30

Argumentum ad verecundiamThe referred-to authority is in fact not an

expect. This fallacy is commonly seen in TV shows and advertisements.

Page 31: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

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Page 32: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

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Page 33: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

10. Appeal to Ignorance33

You commit this fallacy if you reason as follows:- Since we cannot prove that P is false, so P is true; or- Since we cannot prove that P is true, so P is false. Example

You cannot prove that CY Leung was lying. So he did not lie.

Page 34: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

10. Appeal to Ignorance34

Some exceptions occur in the courtroom such as the concept of innocent until proven guilty.

But in general, appeal to ignorance is a bad support for your view.

Page 35: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

11. Fallacy of Hasty Generalization35

Small and non-random samples are non-representative (or biased) samples.

We commit this fallacy by generalizing non-representative samples into general rules.

Page 36: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

Sources of Hasty Generalization36

1. Small sample sizeE.g. There is no racial discrimination in the

US. Otherwise, Obama cannot be the president.

2. Non-random samplingE.g. 95% of people interviewed in the

occupied area support the Occupy Movement. So 95% of HK people support the Occupy Movement.

Page 37: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

12. Fallacy of False Cause37

The link between the conclusion and the premises depends on the assumption of a non-existent or minor causal connection.

ExampleTom was seen in the vicinity of the broken window at about the time that it was broken, so he must have done it.

Page 38: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

13. Fallacy of Slippery Slope38

The link between the conclusion and the premises depends on the claim that a certain event will initiate a chain of events leading to some undesirable consequences, and there is no sufficient reason to think that the chain of events will actually take place.

When we think too far back or ahead, we fall into the slippery slope.

ExampleWe shouldn’t listen to what the animal rights activists say. If they sell us on the idea that pigs have rights, then it will be chickens. Next it will be fishes and other seafood. The starvation of human race will follow close behind.

Page 39: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

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Page 40: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

14. Weak Analogy40

This occurs in an analogical arguments when there may be differences between the two analogates that can weaken the argument.

ExampleSubstances will move from a region of higher

concentration to lower concentration. So money will move from the rich to the poor.

Page 41: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

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Page 42: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

THE PREMISES PRESUME WHAT THEY PURPORT TO SHOW

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Fallacies of Inappropriate Presumption

Page 43: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

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15. Begging the question

It presumes the truth of a premise that is needed to provide adequate support for the conclusion.

This fallacy has 3 forms: A) Leave out a crucial premise.

E.g.: It is morally impermissible to have abortion because killing innocent human beings is always impermissible.

Page 44: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

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B) Present a premise that more or less has the same meaning as the conclusion. E.g.: Murderers should receive capital

punishment, because it is the most just punishment for murder.

Page 45: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

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C) Restate the conclusion as a premise in a long chain of inference.

E.g.: Picasso is the greatest artist of the 20th century. Art critics have described him in these terms. These art critics are correct in their assessment because they have a more keenly developed sense of appreciation than laymen. Their sense is trustworthy because, in order to realize Picasso is the greatest artist of the 20th century, that sense is required.

Page 46: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

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Page 47: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

16. Fallacy of Complex Question47

A doubtful proposition is presumed to be acceptable to the respondent when the question is asked.

Example1. How often do you beat your wife?

2. When was the last time you cheat in the exam?

Page 48: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

17. False Dichotomy48

A dichotomy is a pair of alternatives that are both mutually exclusive and jointly exhaustive.

A pair {X, Y} is mutually exclusive if X and Y cannot both be true.

A pair {X, Y} is jointly exhaustive if either X or Y is true.

A false dichotomy is committed when the arguer presents a pair of alternatives as if they are a pair of dichotomy.

Page 49: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

Not Jointly Exhaustive49

A. From a disjunctive premise, the arguer can deny one of the alternative and conclude the other. But in fact the alternatives are not jointly exhaustive.

ExampleEither you are clever or you are stupid. Yet you are not clever. So you must be stupid.

Page 50: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

Not Mutually Exclusive50

B. One of the alternatives is affirmed and the denial of the other is concluded. But in fact the alternatives are not mutually exclusive.

ExampleEither you are lying or I am lying. Since you are lying, I am not lying.

Page 51: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

AN EXPRESSION IS AMBIGUOUS IF IT IS SUSCEPTIBLE TO DIFFERENT

INTERPRETATIONS IN A GIVEN CONTEXT.

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Fallacies of Ambiguity

Page 52: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

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A) Dangling modifiersE.g.:

Killing his wife, the judge sentenced the husband to ten years of imprisonment.

Page 53: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

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B) Ambiguous reference of pronoun to antecedent

E.g.: Jim tells John that he should turn himself in to the

police. So John must have committed a crime.

Page 54: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

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C) Missing commaE.g.:

The author warns about numerous computational errors in his accounting book. Therefore, he must have written it very carelessly.

Page 55: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

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19. Fallacy of equivocation(not included in the textbook)

This occurs when a word or a phrase is used in two different meanings.

Which word of the following argument has two different meanings?– A good hen is good at reproducing eggs.

Therefore, a good person is good at reproducing babies.

Page 56: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

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• Which word of the following argument have two different meanings?–There is no winning in wars. Take the example of the WWII. Germany of course was the losing side. But Britain also suffered a great loss in economy, lives, and politics. So it was also the losing side.

Page 57: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

WRONG TRANSFERENCE OF A CHARACTERISTIC FROM PARTS TO

WHOLE OR VICE VERSA.

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Fallacies of Grammatical Analogy

Page 58: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

Distributive and Collective Predication58

A characteristic is predicated distributively if it is meant to apply to each and every one of the members of the group.

A characteristic is predicated collectively if it is meant to apply to the group taken as a whole.

“People will die”. “Will die” is predicated distributively to each of the people.

“Human will extinct”. “Will extinct” is predicated collectively to the whole class of human.

Page 59: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

19. Fallacy of Composition59

This occurs when there is a wrong transference of a characteristic from the parts of something to a whole.

Argumentative formBecause each member of X has the property P, the

whole X also has the property P.ExampleEveryone will die some day. It follows that human beings will become extinct someday.

Page 60: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

Composition vs. Hasty Generalization60

Don’t confuse it with hasty generalization in which the conclusion is not an assertion about a group taken as a whole (collective predication). Rather, it is an assertion about every member of a group (distributive predication). Hasty Generalization proceeds from the specific

to the general. Composition proceeds from every member to

the whole class.

Page 61: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

20. Fallacy of Division61

This is the reverse of composition. Now the wrong transference is from whole to parts.

Argumentative formBecause the whole X has the property P, each

member or a member of X also has the property P.

ExampleGood teachers have almost become extinct. Dr. Wong is a good teacher. So he has almost become extinct.

Page 62: Informal Fallacies 1. 2 Formal Vs Informal Fallacies A fallacy is a defect in an argument other than its having false premises. It refers to a defect

Division vs. Accident62

Don’t confuse with fallacy of accident in which the inference is from a general assertion (distributive predication) to a specific assertion. In the fallacy of division the inference is from an assertion about a group taken as a whole (collective predication) to an assertion about the members of the group. Accident proceeds from the general to specific. Division proceeds from the whole class to every

member.