Logical fallacies
FALLACY
A MISTAKE IN REASONING; A DEFECT
IN AN ARGUMENT
Two Types:
• Formal - a defect in the form or
structure of an argument
• Informal - a defect in the content,
material, or the language of the
argument
An argument is like a building.
Just as a building has a structure and
is made out of material, so too does
an argument have a structure and is
made out of material.
The material of an argument is the
language.
Our focus is on informal fallacies.
Such fallacies are committed with the
intent to deceive. Keep in mind that the
person best able to deceive you - to make
his or her argument appear good - is the
person who knows these fallacies. Also
keep in mind that though the argument
may appear to be good, it is not in fact a
good argument but a fallacious one.
There are four basic categories of
informal fallacies:
•
•
•
•
Fallacies
Fallacies
Fallacies
Fallacies
of Relevance
of Presumption
of Ambiguity
in Ordinary Language
These are the fallacies we will be
covering:
• Fallacies of Relevance:
– Appeal to force
• Physical
• Psychological
– Appeal to pity
– Appeal to the People
• Bandwagon
• Vanity
• Snobbery
Fallacies of Relevance, cont.
• Ad hominem
– Abusive
– Guilt by Association
– Tu Quoque
• Appeal to Tradition
• Misplaced Authority
Fallacies of Relevance, cont.
• Hasty Generalization
•
•
•
•
•
Biased Sample
Unknowable statistic
False cause
Non sequitor
Black or White
Fallacies of Presumption
• Begging the Question
• Circular Reasoning
• Suppressed Evidence
Fallacies of Ambiguity
• Equivocation
• Amphiboly
Fallacies in Ordinary Language
•
•
•
•
False Analogy
Slippery Slope
Straw Man
Red Herring
That’s A Lot of Fallacies!!!!!!!!!
So on your next test, you will
have to know, what?
A Lot of Fallacies!!!!!!
Fallacies of Relevance
• Fallacies of this type have one or
both of the following
characteristics:
– the premises are logically irrelevant
to the conclusion
– the connection between the premises
and the conclusion is often emotional
rather than reasonable
Appeal to Force
• Using the threat
of physical or
psychological
force to make
your opponent
concede to your
position.
There are two types of Appeal to
Force
Appeal to Physical Force
• Use the threat of physical harm to
make your opponent concede to
your position.
• This threat can be either against
their person or their property.
Examples
• Agree with me or I will punch you
in the nose. Now don’t you see why
you should agree with me?
• Mrs.Lodato, I think that I should
receive an ‘A’ in this class. I know
you will agree. By the way, I know
where you live.
Appeal to Psychological Force
• Use the threat of psychological
damage to your opponent to get
them to concede to your position.
Examples
• If you do not support your local
charity you will burn in hell.
Therefore, you should support it.
• Mrs. Lodato, I think I should
receive an ‘A’ in this course. I
know you will agree. By the way,
my father is on the Board of
Directors of this college, and he
does everything I tell him to do.
Appeal to Pity
• Here you appeal to
your opponent’s
sympathy to make
them concede to
your position.
• That is, you attempt
to make your
opponent believe
that you will be
miserable unless
they concede to your
position.
Examples
• Student to teacher: You should let me
take the exam over, because if I do not
pass this course, my mother will never
forgive herself, my father will not speak
to me, and even the dog will hate me.
• Lawyer to jury: Please let my client go.
Sure he committed the murders, but it
wasn’t his fault. He had a bad
childhood. His mother left him when he
was 18 and someone stole his puppy
when he was 19.
Appeal to the People
• This fallacy uses our
desires of wanting to
be loved, admired,
esteemed, valued,
recognized, and
accepted by others
to make us concede
to a point or accept a
conclusion.
There are various types of
appeals to the people.
Bandwagon
• Here you argue that
since everyone is
doing something,
your opponent
should do it too,
otherwise he or she
will be left out and
not fit in with the
crowd.
Examples
• Everyone enjoys smoking Whiz, so
you should too
• Don’t be left out in the cold. Come
on in and have a Schlitz!!!!
Appeal to Vanity
• Here someone tells you that if you
use a certain product or accept a
certain point, you will be admired
and sought after like a celebrity
who is said to use the product.
Examples
• Liz Taylor uses Passion perfume,
and young, naked men are after
her. If you use Passion, young and
naked men will be after you.
• Michael Jordan wears Nikke
basketball shoes. If you wear
them, you will play like Michael!!!!
Appeal to Snobbery
• This fallacy tells you
that if you use a
certain product or
concede to a certain
point, that you are
better than
everyone else, a
member of the
select few, and a
rare individual.
Examples
• Advertisement: “Pass the jelly”
• Grey Poupon
• Pierre Cardin luggage - the
luggage that quality people buy
Ad Hominem
• Here you attack
the opponent
rather than the
opponent’s
argument.
There are various types of Ad
Hominem
Abusive
• Here you specifically
attack the person
under question by
calling him or her a
name
Examples
• You should not vote for Al Gore because
he is a ‘liberal’ and will be after your
wallet.
• You can’t trust Joe because he has
shifty eyes
• Why should we believe you? You have a
beard, you smoke cigarettes, and you do
not have a job.
Guilt by Association
• Here you unfairly
judge a person or
his position
because of the
company they
keep, or because
he was associated
with a negative
past event.
Examples
• He must be guilty, because three of
his friends are in jail.
• You should not re-elect Kennedy.
Wasn’t his nephew convicted of
murder?
• Don’t date Harriet. I dated her
cousin and all she was after was
my money.
Tu Quoque
‘You Too’
‘Two Wrongs Make A Right”
• This fallacy is
committed when a
speaker, trying to
show that he is not
at fault, argues that
his opponent has
said or done things
just as bad as he,
the speaker, has
been accused of.
Examples
• Son to father: Sure I smoke dope dad,
but you drink and that is just as bad.
• Daughter of mother: I should be
allowed to date at age 12. You got
married when you were 16.
• Politician: Sure I have made mistakes,
but candidate X has admitted to
committing adultery.
Misplaced Authority
• This fallacy is committed when
testimony from an authority is
used as evidence in an argument,
but the authority quoted is not an
authority in the field under
discussion.
Examples
• Wear Leggs pantyhose. Joe Namath
says they are comfortable
• Psychologist to jury: The defendant
does not suffer from schizophrenia. I
ought to know, I have a Masters degree
in Grief Therapy.
• Our foreign policy needs revision. Just
look at the experts who support my
view: Miss Piggy, fifteen logic
professors, and five taxi cab drivers.
Appeal to Tradition
This fallacy is committed when it is argued that
because something
was done a certain way in the past, it should continue
to be done that way.
Examples
• Women should not work outside
the home. My mother did not
work, my grandma did not work,
and neither will you.
• What do you mean I need to
change my History text? I have
been using this text for the past 50
years and I will continue to use it.
Who cares if it is out of print?
Hasty Generalization
• This fallacy is
committed when
the reasoner
‘rushes to
judgment’ or a
conclusion based
on too little
evidence.
Examples
• The first two apples I took out of
that barrel had holes in them, so
probably all of the apples in that
barrel have holes in them.
• He must be poor. He has a beard
and is wearing dirty clothes. We
should give him some money.
Biased Sample
• This fallacy is
committed when
the sample used
as evidence in an
argument is not
representative of
opinions being
generalized
about.
Examples
• 100% of the people surveyed believe
that drunker driving laws are too strict.
(note: the survey was taken outside of
liquor stores and bars)
• 100% of the people surveyed believe
that abortion is wrong. (note: the
survey was given to people on their way
out of church on Sunday morning)
Unknowable Statistic
• This fallacy is committed when you
cite as evidence statistics that
simply cannot be known by
anyone.
Examples
• The majority of
people, although
they will never
admit it, believe that
abortion is wrong.
• 80% of people
world-wide believe
that there are aliens
from other planets
among us.
False Cause
Post Hoc, ergo Propter Hoc
This fallacy is committed when you assert that because
two events
occur one after the other, that the first is the cause of the
second.
Examples
• Lightning flashed and then the
lights went out. The lightning
caused the lights to go out.
• You went in Harriet’s hospital
room and then she died. You killed
her.
Non Sequitor
This fallacy occurs when the premises of an argument are entirely
irrelevant to the conclusion drawn.
Examples
• Plato wrote in dialogue form and it
is difficult to separate his views
from those of his opponents. So he
is a lousy philosopher.
• You did not do your homework
today, so you must be a rotten
husband to your wife.
Black or White
• This fallacy is committed
when you argue that
since you opponent
doesn’t agree with your
position, then he must
agree with the extreme
of your position. You try
to make you opponent or
audience think that there
are only two choices
(yours and the extreme),
when in fact there are
many.
Examples
• So you don’t think that prisoners should
be allowed to watch cable. Well, you
would have them all in isolation, and
eating nothing but bread and water.
• You don’t believe in buying diamonds
for Valentine’s Day? Well, you must
think that all women are just here to
serve and slave for you.
Fallacies of Presumption
Fallacies of Presumption
• These fallacies occur when the
arguments presume - in some way what they are trying to prove, or they
presume evidence of some type.
There are Many Types of Fallacies of
Presumption
Begging the Question
• This fallacy occurs when the arguer
presents evidence for the conclusion as
true, but the evidence presented is
either an opinion or the arguer offers
no proof that the evidence is in fact
true.
Examples
• To be a good president, it is necessary to
have at least 30 years of political experience.
Jesse Jackson has not had that much political
experience, so he would not make a good
president.
• To be a good student, you must study at least
four hours per night, per subject. Harry
works all night and does not have time to
study that long. He will fail.
Circular Reasoning
• This fallacy is
committed when the
argument fails to
prove anything
because it takes for
granted what it is
supposed to prove.
Examples
• Beautiful women are the best type to
date because they are beautiful and fun
to date.
• Candidate X must not be trusted
because he is deceptive.
• Abortion is wrong because it is immoral.
• Smoking marijuana is wrong because
taking drugs is wrong.
Suppressed Evidence
• This fallacy is committed when relevant
evidence is purposely omitted in the
argument because it is contrary to what
the author is trying to prove.
Examples
• R.J. Reynolds Tobacco Company memos
• “Jesse Jackson will not make an effective
president because he has never held political
office.” Here, the arguer fails to make note of
the fact that Jackson does have experience in
foreign policy, and he also fails to note that
there have been other presidents who never
held political office before becoming
president.
Fallacies of Ambiguity
These fallacies occur when one word in an argument may be
taken to have two or more distinct meanings.
Equivocation
• This fallacy occurs when the same word
is used in two different senses in an
argument.
Examples
• Every mystery is a religious belief and
the whereabouts of the killer is a
mystery. Therefore, the whereabouts of
the killer is a religious belief.
• Computers get viruses and you have a
virus so you must be a computer.
Amphiboly
• This fallacy occurs
when the grammar
of a statement is
ambiguous and
allows for more than
one interpretation.
Examples
• Save trash and
waste paper
• Rummage sale ad:
“The ladies will have
cast off clothing in
the church
basement.”
Fallacies in Ordinary Language
False Analogy
• This fallacy is committed when you
compare two items, and argue that
because they have some characteristics
in common, they must have another
characteristic in common. However, you
ignore or fail to point out relevant
dissimilarities.
Examples
• A computer has a memory, can make
predictions and can store information.
The human mind also does these
things. The human mind also dreams,
so computers can dream as well.
• Note: Here the arguer fails to take into
consideration relevant differences
between the human mind and a
computer.
Slippery Slope
• Here it is argued that if
one event is allowed to
occur, then a whole
series of consequences
will also occur. Or if
you accept one point,
then you must accept a
series of other points.
The consequences may
be either good or bad.
Examples
• Mother to daughter (who is on a diet): “If
you eat that donut, then you will eat the
whole box, and then you will gain back all of
your weight, and then you will have to buy all
new clothes and and a new car, and you will
never get married.
• Mother to daughter: If you lose weight, you
will become a beauty queen, and then a
movie star, etc.
Straw Man
• Here the arguer
misinterprets or
misrepresents an
argument or position for
the purpose of attacking
it. He or she then
concludes that the real
position has been
refuted, when in fact
the misrepresentation
was refuted.
Examples
• Mr. X states: “My opponent in this debate
has argued that our prisons release hardened
criminals back into society. He recommends
more rehabilitation. He mentioned job
training, therapy, and other educational
programs. Well, I certainly don’t like all the
prison riots and so forth,but I don’t think that
we should change prisons into schools and
hospitals, and certainly not vacation
resorts!!!!”
Red Herring
• You commit this
fallacy when you
introduce a “logically
separate and
irrelevant issue into
the discussion.”
Examples
• You say that abortion is wrong and that it is
murder. But do you know how many other
‘murders’ are committed by incompetent
doctors everyday? A lot, that’s how many.
• You say that women should have the same
rights as men? Now why is such a beautiful
woman like yourself worried about such
things? You should be worried about getting
a rich husband.