Introduction to Logical
Fallacies
Morales
English 101/120
Goya’s “Sleep of Reason Produces Monsters”
Why Study Logical Fallacies?
• Even if you could count on reasoning
correctly 100% of the time, you cannot
count on others doing so. In logical selfdefense, you need to be able to spot poor
reasoning, and—more importantly—to
understand it. To be able to correct others'
mistakes, or to refute them convincingly,
you need to understand why they are
wrong. (fallacyfiles.com)
Hasty
Generalization/Overgeneralization
• Women make bad bosses.
--Don’t make judgments based on insufficient
evidence.
• Politicians are crooked.
--Don’t assume that all members of a group
have the qualities of some.
• British people are very cold and uptight.
--Never use “all” or “none” statements.
• African-Americans can sing beautifully.
The Argument Based on Tradition
--Tradition doesn’t
The death
penalty
is nothing new.
necessarily
make
it
People have been executed for
moral
or
ethical.
thousands of years, in many societies.
--Such
arguments
mayfor over two hundred
Slavery
has existed
not address
years andthe
the current
negro is accustomed to his
lifestyle of servitude. What would become of
situation
him without it?
--The needs of society may
great society has provided state
haveEvery
changed.
funding for art and culture.
Ad Hominen Attack
--Don’t resort to cheap shots.
Why should we trust George Bush’s ideas
about foreign policy when he is nothing
--Tackle the tough points.
more than a recovering cocaine addict?
--Do your homework; find the facts
How can Susan Sarandon, an actress,
blabber
about
issues
like the
death
--Attack
the
issues,
not
the person!
penalty when she hasn’t even been to
college?
?
Begging the Question
This must be proven
We shall justify making abortion illegal.
1. Abortion is unjust murder.
2. Murder is illegal.
3. Therefore abortion should be made
illegal, since it is murder.
Post
Hoc,
Ergo
Propter
Hoc
(after
Today a black cat caused me to break my
this, therefore,
this)
ankle!
It crossed in because
front of me,of
and
ten
minutes later, I tripped on the curb!
--Don’t assume that an earlier event
Evercaused
since Villaraigosa
became mayor, the
the situation.
crime rate has increased! He’s going to
ruin our
city! factors may have
--What
other
contributed to the situation?
Most rapists read pornography; therefore,
--You
must prove
theviolence
connection
pornography
causes
against
women. two events
between
Either/Or Fallacy
Either you’re with us, or you’re against us
Gerda Reith is convinced that superstition can be
a positive
force.
"It gives youmore
a sense than
of controltwo
--There
are
usually
by making you think you can work out what's
options.
America.
Love it or leave it.
going to happen next," she says. "And it also
makes you feel lucky. And to take a risk or to
enter into a chancy
situation,
you really have to
--Arguments
are
complex
believe in your own luck. In that sense, it's a very
useful way of thinking, because the alternative is
--Don’t
your
audience’s
fatalism,underestimate
which is to say, 'Oh, there's
nothing
I can
do.' At least superstition makes people do things."
intelligence
(Source: David Newnham, "Hostages to
Fortune“)
Slippery Slope
If we legalize marijuana, the next thing we
know, kids will be shooting up heroin,
smoking crack, and going crazy with LSD.
--Don’t assume that one event will
Iflead
we make
homosexual marriages legal,
to another.
pretty soon it’ll be acceptable to marry
one’sconnections
uncle or one’s father,
an
--These
must or
beeven
proven.
animal!
--If you can, in fact, show a connection,
then it’s not a fallacy.
Card Stacking/ Slanting
Georgeignore
Washington,
the “father”
of our
-- Don’t
evidence
that may
weaken
your
argument.
country, was
actually
a slaveholder and a
Acknowledge
pot-smoker. Whyit!
do celebrate his birthday
as a national holiday?
--Don’t use words that show extreme
prejudice and disapproval.
Gay marriage should not be legalized
because
homosexuality
a sin and
--Treat
your
opponentsiswith
respect.
homos are disgusting perverts.
Major Fallacies Review
•
•
•
•
•
•
•
•
Overgeneralization/ Hasty Generalization
Argument Based on Tradition
Ad Hominem Attack
Ignoring (begging) the Question
Post Hoc, Ergo Propter Hoc
Either/Or Fallacy
Slippery Slope
Card Stacking/ Slanting
I lost my wallet yesterday. I knew that walking
under that ladder would be trouble!
POST HOC: ONE EVENT DID NOT NECESSARILY CAUSE THE OTHER
Yesterday, my neighbor’s sixteen-year old son
zoomed out of the driveway and almost hit my little
daughter. Last week, a teenager rear-ended my car.
When are we going to raise the driving age to 21?
Hasty Generalization: Not enough evidence
How can she be guilty of that crime? She has such a
lovely family—they go to church regularly and they
are such friendly people!
Hasty Generalization: judgment based on stereotype
Of course she’s poor. Look at that torn coat she’s
wearing.
Hasty Generalization/ Stereotype
How can George Bush understand the plight of poor
people? He was born with a silver spoon in his
mouth. Cardstacking: Ad Hominem Attack
This unfair rule of making students do useless
community service work must be changed.
We should either pay our children’s teachers
better salaries or just admit that we don’t
give a damn about education.
How do you know that life doesn’t exist on
other planets?
Christopher Columbus should not be considered
a hero. He massacred Native Americans and
stole their land.
If the exam is too difficult, students will fail, and
then they’ll want to drop out of school.
If we pass laws against fully-automatic weapons, then it won't be long
before we pass laws on all weapons, and then we will begin to restrict
other rights, and finally we will end up living in a communist state.
Thus, we should not ban fully-automatic weapons.
If I make an exception for you then I have to make an
exception for everyone.
You claim that Mr. Jones is innocent, but why should anyone listen to you?
You are a Mormon after all.
You may argue that God doesn't exist, but you are just a big fat idiot.
"Adding meat to his diet helped make him physically stronger," says Jeff
Twiss, an officer of the team. "The doctors convinced him he needed
meat."
Smith, who is from England, decides to attend graduate school at
Ohio State University. He has never been to the US before. The day
after he arrives, he is walking back from an orientation session
and sees two white (albino) squirrels chasing each other around a
tree. In his next letter home, he tells his family that American
squirrels are white.
The Brookings Institute sampled 500 liberal non-religious males
living in San Francisco regarding the issue of gay marriage in
America. Most of them approved, therefore most Americans
everywhere must approve of gay marriage
Marriage is one of humanity’s oldest institutions, and it wouldn’t
have survived so long as an integral part of every culture if it were
not for the fact that it is vital for our survival. Therefore, we
shouldn’t tamper with it or do anything that might harm it.
The only policy that effectively reduces public shootings is
right-to-carry laws. Allowing citizens to carry concealed handguns
reduces violent crime.
In the 31 states that have passed right-to-carry laws since the
mid-1980s, the number of multiple-victim public shootings and other
violent crimes has dropped dramatically. Murders fell by 7.65%,
rapes by 5.2%, aggravated assaults by 7%, and robberies by 3%.