LOGIC AND CRITICAL
THINKING
(LoCT 1011)
CHAPTER FIVE:
INFORMAL FALLACIES
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 causal 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.
Fallacies….Cont’d….
In
logical arguments,
fallacies are either formal
or informal.
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Formal Vs Informal Fallacies
A fallacy is a defect in an argument other
than its having false premises.
 An informal fallacy is a defect in the
content of an argument. (A formal fallacy
is a defect in the structure or forms of
an argument.)


We have seen many valid rules of deduction.
Formal fallacies can be understood as a use of
unacceptable rules.
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E.g: 1
All Tigers are animals
All mammals are animals
Therefore, all tigers are mammals
2. If apes are intelligent, then apes can solve puzzles
Apes can solve puzzles
Therefore, apes are intelligent
Informal Fallacies
There are five main types of informal
fallacies, comprising a total of 22 cases.
 There are 5 main types:

A) Fallacies of relevance
B) Fallacies of weak induction
C) Fallacies of presumption
D) Fallacies of ambiguity
E) Fallacies of grammatical analogy.
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A: Fallacies of Relevance
They are arguments where the premises
are not logically relevant to the
conclusion.
 But these premises are psychological
relevant to the conclusion and so as to
give us the impression that the conclusion
is supported by them.

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1. Appeal to force
(Argumentum ad baculum)
In such cases, the arguer uses threat instead
of evidence to force the listener to accept
the conclusion.
 E.g.:


Child to its Playmates: Man United is the best
football club in the world, if you don’t accept this, I am
going to call my brother and he will throw you out!
◦ I deserve an A for my test. You should know that
my father is a good friend of College Principal.
◦ Only fools believe in what he says. You don't
believe in him, don't you?
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2. Appeal to pity
(Argumentum ad Misericordium)
The arguer tries to win support by
evoking pity from the listener.
E.g.:
A Student to her professor: Professor Kebede, it

would be wrong for you to flunk me for cheating. I am a single
mother, and to provide for my two kids. I have to work three jobs.
At the end of the day, I am absolutely exhausted, and after I drag
my weary body home, I have neither the time nor the energy to
study.
 Dawit: I deserve an A in this course, Professor. Not only did I
study during my grama‘s funeral I also passed up thev hear
transplant surgery
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3. Appeal to people
(Argumentum ad populum)
When someone claims an idea or belief is
true simply because it is what most people
believe.
For example: Lots of people bought this
album, so it must be good!
 AP uses the views of MAJORITY as
persuasive device
 In the direct approach, the arguer excites
emotions from the crowd. In the indirect
approach, the arguer appeals to some
individuals by focusing on some aspects of
those individuals’ relationship to the crowd.

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
•
•
Most of the political rhetoric uses the direct
approach.
DIRECT: Address large group of People to win
acceptance for his/ her conclusion
Objective: to arouse a kind of mob mentality
used by nearly every propagandist
◦ E.g.: The Democratic Party labels The DAB Party as
“Defending Government Party” ; whereas the DAB Party
labels the Democratic Party as “Disagreeing Party” .

Usually, the more “poetic” and “subtle” the
expressions are, the more convincing the argument
looks like.
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There are three types of indirect
approach:
 A) Bandwagon Argument: : Large group
or Per cent (%)
 E.g.:

◦ Many students choose this course. Therefore,
you should also take it.
◦ Sure, this is a very fantastic gum with lovely
flavor. That is why the majority of the people
in Addis Ababa chew it than any other gums.
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B) Appeal to vanity: : Associate product
with someone who is admired
 Appeal to our desire to be like someone
who is admired.
 E.g.:
 You have got to see Aba Jambo’s latest film
immediately. It is breaking the country’s film
records in terms of audiences, and every one
is talking about it.

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C) Appeal to snobbery:
 Appeal to our desire to be in a particular
social class.
 E.g:
o Friendship cafe, no doubt, is the best cafe in
Addis Ababa.That is only for distinguished
and very important persons. Come and enjoy
your weekends at Friendship cafe!!
o Master Platinum Card is not for everyone.
You may be one of the select few.

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4. Argument against the person
(Argumentum ad hominem)

The arguer attacks his/her opponent’s
character instead of his/her argument.
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A. Fallacy of ad hominem abusive
Verbally abuse your opponent based on her
background. E.g:
 Ato Gebeyehu has argued for increased
funding for the disabled. But nobody should
listen to his argument. Ato Gebeyhu is a Slob
who cheats on his wife, beats his wife, beats
his kids, and never pays his bills on time.
◦ His words should not be taken because he is
gay.
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



B) Fallacy of ad hominem
Circumstantial
Present your opponent as predisposed to
say in a certain way because of her
circumstance:
E.g.:
Ato Mohammed has just argued that we replace the public
school system with private education. But, of course, he
argues that way. He has no kids, and he does not want to
pay any more taxes for public education.
◦ You should not believe what Donald Tsang promises.
He is going to retire soon so that he does not need
to fulfill any promises.
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



C) Fallacy of ad hominem tu quoque
(you too)
Argue that doing something is right because
your opponent is also doing the same thing
(You, too).
E.g:
Ato Gemechu has just given us reason for why
we should place more emphasis on family
values. But, he has no business talking. Just a
week ago he got divorce.
◦ Teacher:You should not skip class.
Student: I don’t think you have never skipped
class.
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5. Fallacy of accident
Misapply a general rule to a particular
case because the particular case is an
exceptional case (accident) beyond the
scope of the rule.
 E.g.:

◦ Killing is wrong. Mercy killing is a kind of
killing. So mercy killing is wrong.
◦ Children should obey and follow their parents.
Therefore, little Abush should follow his alcoholic
fathers orders to drop out of school and get a job.
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6. Straw Man
During a debate between two sides, one side distorts
its opponent's view (usually as a more extreme
position) and then attacks the distorted argument.
 E.g.:
 Dr. Kebede has just argued against affirmative action for
women. It seems what he is saying is that women should
stay out of the work place altogether. Just keep them
barefoot and pregnant. That is what Dr. Kebede wants.
Well! I think we are all smart enough to reject his
argument.

◦ A: The society should not discriminate gays.
B: So you are saying that everyone should be homosexual.
It's ridiculous.
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When one side argues, "Some X are Y,"
this view can easily be distorted as "All X
are Y."
 E.g.:

A: Smoking is bad to your health. One of ten
deaths is caused by diseases related to
smoking.
B: That cannot be true. My grandfather has
smoked since he was sixteen, and he is still
very healthy.
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7. Fallacy of missing the point
(ignoratio elenchi)



This happens when the premises of an argument
lead, or seem to lead, to one conclusion and then a
completely different conclusion is drawn.
E.g:
Kenenisa Bekele has won many cross country
championships. He is still dedicated, hard worker,
disciplined, courageous and determined to win
marathon.Therefore, Ethiopians should save their lives
from HIV-AIDS.
◦ Many welfare receivers are new immigrants nowadays.
Therefore, we should reduce the number of immigrants.
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8. Red Herring
Red herring fallacy will be committed when an
arguer diverts the attention of the listeners or
readers by changing the original subject to
some totally different issue without notifying
the listeners’ or readers’.
 is an attempt to divert the attention of
audiences to a totally different issue.
 this fallacy ignores the topic under discussion
and shifts the attention of his audiences to
another issue.
 All at a sudden, an arguer changes the subject to
a completely different idea and makes a
conclusion upon this changed idea.

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
E.g.:
Ato Shiferaw, a senior official in water resource
management, has argued that clean water Act
should never be weakened. But the point is that
water is one of the most common substances on
earth. Over two-thirds of our planet’s surface is
covered with water, and massive amounts of
frozen water cover both poles. If the ice caps
were ever to melt, ocean levels would rise several
feet. Obviously the official has been misinformed.
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In many cases, a debate is 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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Straw Man & Red Herring
Straw Man: Arguer has distorted the
opponent's argument.
 Red Herring: Arguer simply diverts
to a new subject.

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LESSON TWO
B: Fallacies of Weak Induction





These are different from the fallacies of
relevance in that the premises are not
logically irrelevant to the conclusion.
Rather, the defect is that the connection
between the premises and the conclusion is
not strong enough.
Fallacies of weak induction are typically an
instance of inductive arguments.
premises are not sufficient to arrive at the
conclusion,
Therefore, these are cases of weak inductive
argument. There are 6 types of such fallacies.
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9. Appeal to unqualified authority
(Argumentum ad verecundiam)
The referred-to authority is in fact not an
expert. Many TV shows and advertisements
use stars and famous people to promote
products and ideas.
 E.g.:

Professor Chala, who is a respected physician in this country,
argued this morning that all buildings found in Addis Ababa
have less quality. It implies that, all buildings of Addis Ababa
have less quality.
 Omer, who is a well-known astronomer, says that AIDS epidemic
is caused by a perverse alignment of the planets, and that there is
nothing anyone can do about it. Therefore, we can only conclude
that all of these efforts to find a cure for AIDS are wastage of
time.

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10. Appeal to Ignorance
occurred when an arguers conclusion is
supported by his/her own ignorance and lack
of evidence
 You commit this fallacy when you make the
following reasoning:

◦ 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.

E.g.:
◦ You cannot prove that spirits do not exist. So
there are really spirits.
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Nobody has ever proved the existence of
ghosts.Therefore, we have no alternative but
to conclude that ghosts are mere figments of
the imagination.
 People have been trying for centuries to
prove that God exists. But no one has
yet been able to prove it. Therefore, God
does not exist.

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11. Fallacy of hasty generalization
(converse accident)
is committed when a person or an arguer
makes assumptions about a whole group
based on a sample that is inadequate or
unrepresentative.
 This is about the representative
appropriateness of sampling.
 Small and non-representative samples are
sources of error.

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We try to generalize non-representative
particular cases into general rules.
 The non-representative cases include nonrandom samples and small size samples.
 E.g.:
Six Arab fundamentalists were convicted of
bombing the World Trade Center in New
York City. The message is clear: Arabs are
nothing but a pack of criminals.

◦ You should try this cold-medicine. It works for
me.
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12. Fallacies of false cause





1.
2.
3.

is committed when the arguer in his or her argument
oversimplified the cause of a certain event
makes a kind of confusion between the cause and effect, or
identifies a certain event as the cause of an other event
merely on the ground that the first event, which the arguer
identifies as a cause, occurs before the new action.
The link between the conclusion and the premises depends on the assumption
of a non-existent or minor causal connection.
It has three varieties:
post hoc ergo propter hoc (‘‘after this, therefore on account of this’’).
Non causa pro causa (‘‘not the cause for the cause’’)
Oversimplified cause
E.g.: 1
◦ During the past two months, every time that the Chelsea wore
blue clothes while playing foot ball and defeated. Therefore, to
prevent defeats in the future, the Chelsea should get rid of those
blue clothes.
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For example 2: A black cat crossed my path and
later I tripped and sprained my ankle. It must be
that black cats really are bad luck.
 For example 3: The quality of education in RVU
has been declining for years. Clearly, our teachers
just aren’t doing their job these days.

13. Fallacy of slippery slope
The link between the conclusion and the
premises depends on the claim that a certain
event or situation will initiate a more or less
long chain of events leading to some
undesirable consequences, and when there is
not 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.

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
E.g.:
◦ We shouldn’t listen to what the animal rights activists
say. If they sell us on the idea that pigs and cows have
rights, next it will be chickens and ducks. Next it will
be fishes and other seafood. The starvation of human
race will follow close behind.
◦ It is not a good idea to put your child in a day care center.
Separation from parents causes isolation and alienation,
and soon the child becomes incapable of relating to other
children, and this inability to relate causes depression. As
the child gets older, the depression leads to psychosis.The
final result is either suicide or a life wasted in a mental
institution.
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14. Weak analogy
This occurs in inductive arguments from
analogy when the analogy between two things is
not strong enough to support the conclusion.
 is occurred when the two things that are being
compared are not really similar in the relevant
respects.
 Argument form:
◦ Entity A has attributes a, b, c, d, and z.
◦ Entity B has attributes a, b, c, and d.
◦ Therefore, entity B probably has attribute z
too.

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
E.g.:
1. The flow of electricity through a wire is
similar to the flow of water through a pipe.
When water runs downhill through a pipe, the
pressure at the bottom of the hill is greater
than it is at the top. Thus, when electricity
flows downhill through a wire, the voltage
should be greater at the bottom of the hill than
at the top.
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2. Melkamu’s car is red, has a speed of 180
km per hour and made in Italy. My sister’s
new car is also red, and has a speed of
180 km per hour. Therefore, it probable is
made in Italy.

Compare good and bad analogies:
◦ Peter is fat and has long hair. He gets A in
Logic. Paul is also fat and has long hair.
Therefore, he will also get A in Logic.
◦ Peter is smart and diligent. He gets A in Logic.
Paul is also smart and diligent. Therefore, he
will also get A in Logic.
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C: Fallacies of Presumption
To presume means to take something for
granted or to assume a given idea as true or
correct, which in fact needs further proof,
explanation or evidence.
 These fallacies arise because the premises
presume what they purport to show.
 Fallacy of presumption will be committed
when the assumption given in the premise is
not supported by proof, but the arguer
maintains that it does not need proof and
s/he invites his/her audiences to accept it as
it is.

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These fallacies usually contain tricky and
confusing phraseologies for the purpose
of concealing or hiding the wrong ideas
stated in the premise.
 There are four types of fallacies that are
considered as fallacies of presumption.

15. Begging the question/Circular
reasoning (Petitio Principii)





occurs when the arguer, without providing real
evidence, asks the readers or listeners to simply accept
the conclusion of his argument.
Sometimes this argument is called circular reasoning
because the argument relies on a premise that says
samething as the conclusion.
An argument committing this fallacy creates the illusion
that inadequate premises provide adequate support for
a conclusion.
It presumes the truth of a premise that is needed to
provide adequate support for the conclusion.
One way of doing so is formulating premise and
conclusion of an argument in two slightly different ways.
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This fallacy has 3 forms:
 A) Leave out a crucial premise.
 E.g.:

◦ Humans and apes evolved from common
ancestors. Just look how similar they are.
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B) Present a premise that more or less has the
same meaning as the conclusion.
 E.g.:
◦ We can be certain that this photo is of Aba Jifar
because the person in the photo looks just like
him.

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

C) Restate the conclusion as a premise in a long chain
of inference.
E.g.:
◦ Ford Motor Company clearly produces the finest cars
in the United States. We know they produce the finest
cars because they have the best design engineers. This
is true because they can afford to pay them more than
other manufacturers. Obviously they can afford to pay
them more because they produce the finest cars in the
United States.
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16. Fallacy of complex question
This occurs when an apparently single
question is asked that really involves two
or more questions.
 E.g.:
o Have you stopped in involving such crimes?
o if I ask “What did you eat in lunch?” I am
in fact asking a) Did you have lunch? b) if
you did, what did you eat?

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17. False of dichotomy





This fallacy is committed when the arguer insists
that only two alternatives are possible in a given
situation
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.
It 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.
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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.
E.g.:



Either we elect Democrats, or the country’s fate will be
worsened.The choice should be obvious.
Either you study in Oxford or you miss the best
chance of your life. Yet you cannot enter Oxford. It
is clear that you have missed your best chance in
life.
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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.

E.g.:
◦ Either you are lying or I am lying. Since you are lying, I
am not lying.
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18. SUPPRESSED EVIDENCE
 the fallacy of suppressed evidence occurred
when the arguer knowingly or unknowingly
suppressed or omits important evidence
 occurred when the person who presents an
argument intentionally or unintentionally
conceals or hides significant evidence from
his or her argument.
 fails to support his or her position and
emphasizes on some other reasons that are
not as such important to the conclusion of
the argument.
 Committed when True and Relevant
information is left out for any resaon.
Addis Ababa University deserves to be one of
the best Universities in Africa as it has
impressive buildings, beautiful gates, and an
attractive fountain.
 Maradona of Argentina is a prominent and
good foot ball player in the world,
because the behavior of Maradona is
good, his clothing is attractive and the
large amount of money that his country is
paying for him.

D. Fallacies of Ambiguity
An expression is ambiguous if it is susceptible
to different interpretations in a given context.
 arises from the occurrence of some form of
ambiguity in either the premise or the
conclusion of the argument.
 When the conclusion of an argument depends
on a shift in meaning of an ambiguous
expression or on the wrong interpretation of
an ambiguous statement, the argument commits
a fallacy of ambiguity.

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19. EQUIVOCATION



occurs when the conclusion of an argument
depends on the fact that a word or phrase is
used, either explicitly or implicitly, in two
different senses in the argument.
Example 2: Any law can be repealed by the
legislative authority. But the law of gravity is
a law. Therefore, the law of gravity can be
repealed by the legislative authority.
Giving money to charity is the right thing to
do. So charities have a right to our money
20. Fallacy of amphiboly
occurs when the arguer misinterprets a statement
that is ambiguous and proceeds to draw a
conclusion based on this faulty interpretation.
 is created when the arguer intentionally or
unintentionally provides an argument which
involves an ambiguous grammatical construction
that can be understood in two ways.
Example :
 Our engineering school teaches us how to build
a house in three years.
 Lalise said that she painted her picture hanging on
the wall of her bedroom. Obviously Lalise is quite an
acrobat.

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Common Characterstics
 Arguments that commit these fallacies are
grammatically analogous to other
arguments that are good in every respect.
Because of this similarity in linguistic
structure, such fallacious arguments may
appear good yet be bad.
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E. Fallacies of Grammatical Analogy

Arguments that commit these fallacies are
grammatically analogous to other arguments
that are good in every respect.
 They
usually involve a wrong
transference of a characteristic from
parts to whole or vice versa.
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




We need to know about distributive and collective
predication of a characteristic.
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.
“Human will extinct”. “Will extinct” is predicated
collectively to the whole class.
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21. Fallacy of composition

This occurs when there is a wrong transference
of a characteristic from the parts of something
to a whole.

Argument form: Because each member of
X has the property P, the whole X also
has the property P.

E.g.:
◦ Each singer in the choir sings well. It follows
that the choir sings well.
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
E.g.:
◦ Each singer in the choir sings well. It follows
that the choir sings well.

Each player on this basketball team is an excellent
athlete. Therefore, the team as a whole is excellent.
Each atom in this piece of chalk is invisible. Therefore,
the chalk is invisible.
Sodium and chlorine, the atomic components of salt, are
both deadly poisons. Therefore, salt is a deadly poison.


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22. Fallacy of division
Exact reverse of composition.
 The fallacy of Division is occurred because of
the wrong or erroneous transference or
association of the attributes of the whole onto
its parts.
 Argument form: Because the whole X has the
property P, each member or a member of X
also has the property P.

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
Example 1: Salt is a nonpoisonous compound.
Therefore, its component elements, sodium and
chlorine, are nonpoisonous.
Example The ball is blue; therefore the atoms
that make it up are also blue.
Example 3: The Royal Society is over 300 years
old. Professor Thompson is a member of the
Royal Society. Therefore, Professor Thompson
is over 300 years old
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THE END.
THANKS!
GALATOOMAA!