Informal Fallacies
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Formal Vs Informal Fallacies
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 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.
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 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
Informal Fallacies
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 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
Fallacies of Irrelevance
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THE PREMISES ARE
PSYCHOLOGICALLY RELEVANT, BUT
NOT LOGICALLY RELEVANT, TO THE
CONCLUSION.
1. Appeal to Force
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Argumentum ad baculum
 The arguer uses threat instead of evidence to force
the listener to accept the conclusion.
Example
Student: I deserve an A in the course. You know
that my father is a good friend of the
College Principal.
2. Appeal to Pity
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Argumentum ad misericordium
 The arguer tries to win support by evoking pity from
the listener.
3. Appeal to People
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Argumentum ad populum
 Direct 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.
Direct Approach
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 Most of the political rhetoric uses the direct
approach to arouse your favorable impression or
resentment.
Example
 Describe CY Leung as a “wolf.”
 Label national education as “brainwashing
education.”
3 Types of Indirect Approach
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A.
Bandwagon argument
 The arguer attempts to persuade the listener by
appealing to group pressure.
Example
 Many students choose this course. Therefore, you
should also take it.
3 Types of Indirect Approach
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B.
Appeal to vanity
 Appeal to the pride or conceit of the listener in order
to get them to do something.
Example
 Only fools believe what CY Leung says.
3 Types of Indirect Approach
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C.
Appeal to snobbery
 Appeal to desire of the listener of being in a
particular social class.
Example
 Only the selected few can own a platinum card.
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4. Argument against the Person
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Argumentum ad hominem
 The arguer attacks the opponent’s character instead
of his/her argument.
3 types of ad hominem
 Background attack
 Circumstance attack
 You too
Background Attach
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A.
Abuse your opponent based on her background.
Example
CY Leung’s words should not be taken
because he is a communist.
Circumstance attack
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B.
Present your opponent as predisposed to say or
act in a certain way because of her circumstance.
Example
All the policies of CY Leung aim to protect the
interests of Mainland because he tries to win the
trust of the Central Government.
You too
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C.
Argue that doing something is right because
your opponent is also doing the same thing.
Example
Teacher: You should not
skip class.
Student: I don’t think
you haven’t skipped one.
5 – Fallacy of Accident
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 Misapply a general rule to a particular case because
the particular case is an exceptional case (accident)
beyond the scope of the rule.
Example
Exceeding the speed limit
is illegal. Ambulance
drivers always exceed the
speed limit during
emergency. Thus, their
action is illegal.
6. Straw Man
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 During a debate between two sides, one side distorts
its opponent's view (usually as a strengthened
position) and then attacks the distorted argument.
Example
A: The society should not
discriminate gays.
B: So you are saying the
everyone should be homosexual.
It’s ridiculous!
Example
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 When one side argues that “Some X are Y”, this view
can easily be distorted as “All X are Y”.
Example
A:
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.
7. Fallacy of Missing the Point
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Ignoratio elenchi
 This happens when the premises of an argument lead,
or seem to lead, to one conclusion but then a
completely different conclusion is drawn.
Example
Many welfare receivers
are new immigrants.
Therefore, we should
reduce drastically the
number of immigrants.
8. Red Herring
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 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.
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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.
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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?
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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.
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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.

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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.
Fallacies of Insufficiency
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THE PREMISES ARE NOT STRONG
ENOUGH TO JUSTIFY THE
CONCLUSION.
9. Appeal to Unqualified Authority
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Argumentum ad verecundiam
 The referred-to authority is in fact not an expect.
This fallacy is commonly seen in TV shows and
advertisements.
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10. Appeal to Ignorance
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 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.
10. Appeal to Ignorance
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 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.
11. Fallacy of Hasty Generalization
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 Small and non-random samples are non-
representative (or biased) samples.
 We commit this fallacy by generalizing nonrepresentative samples into general rules.
Sources of Hasty Generalization
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1. Small sample size
E.g. There is no racial discrimination in the US.
Otherwise, Obama cannot be the president.
2. Non-random sampling
E.g. 95% of people interviewed in the occupied area
support the Occupy Movement. So 95% of HK people
support the Occupy Movement.
12. Fallacy of False Cause
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 The link between the conclusion and the premises
depends on the assumption of a non-existent or minor
causal connection.
Example
Tom was seen in the vicinity of the broken window at about the
time that it was broken, so he must have done it.
13. Fallacy of Slippery Slope
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 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.
Example
We 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.
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14. Weak Analogy
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 This occurs in an analogical arguments when there may be
differences between the two analogates that can weaken the
argument.
Example
 Substances will move from a region of higher
concentration to lower concentration. So money will
move from the rich to the poor.

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Fallacies of Inappropriate
Presumption
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THE PREMISES PRESUME WHAT THEY
PURPORT TO SHOW
15. Begging the question
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 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.
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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.
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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.
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16. Fallacy of Complex Question
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 A doubtful proposition is presumed to be acceptable
to the respondent when the question is asked.
Example
1. How often do you
beat your wife?
2. When was the last
time you cheat in the
exam?
17. False Dichotomy
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 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.
Not Jointly Exhaustive
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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.
Example
Either you are clever or you are stupid. Yet you are not clever.
So you must be stupid.
Not Mutually Exclusive
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B.
One of the alternatives is affirmed and the
denial of the other is concluded. But in fact the
alternatives are not mutually exclusive.
Example
Either you are lying or I am lying. Since you are lying, I am
not lying.
Fallacies of Ambiguity
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AN EXPRESSION IS AMBIGUOUS IF IT
IS SUSCEPTIBLE TO DIFFERENT
INTERPRETATIONS IN A GIVEN
CONTEXT.
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 A) Dangling modifiers
 E.g.:
 Killing
his wife, the judge sentenced the
husband to ten years of imprisonment.
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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.
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 C) Missing comma
 E.g.:

The author warns about numerous computational errors
in his accounting book. Therefore, he must have written it
very carelessly.
19. Fallacy of equivocation
(not included in the textbook)
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 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.
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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.
Fallacies of Grammatical
Analogy
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WRONG TRANSFERENCE OF A
CHARACTERISTIC FROM PARTS TO
WHOLE OR VICE VERSA.
Distributive and Collective Predication
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 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.
19. Fallacy of Composition
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 This occurs when there is a wrong transference of a
characteristic from the parts of something to a whole.
Argumentative form
 Because each member of X has the property P, the whole X
also has the property P.
Example
Everyone will die some day. It follows that human beings will
become extinct someday.
Composition vs. Hasty Generalization
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 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.
20. Fallacy of Division
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 This is the reverse of composition. Now the wrong
transference is from whole to parts.
Argumentative form
 Because the whole X has the property P, each member or a
member of X also has the property P.
Example
Good teachers have almost become extinct. Dr. Wong is a
good teacher. So he has almost become extinct.
Division vs. Accident
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 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.