Transcript Informal Logic, Famous Fallacies

Don’t Be Fooled by Bad Arguments
Distinguish arguments from
explanations:
Arguments are the assertion of a
conclusion from reasons that are better
known than the conclusion.
Explanations are the assertion of reasons
for a conclusion that is better known
than those reasons.
Bill punched Bob in the nose.
Bob is in pain.
Warm, moist air hit a cold front.
It is raining.
Fallacies of Relevance:
Appeal to Force
Appeal to Pity
Appeal to the People
Ad Hominem
Accident
Straw man
Missing the Point
Red Herring
Fallacies of Presumption:
Begging the Question
Complex Question
Faulty Dilemma
Weak Induction:
Appeal to Unqualified Authority
Appeal to Ignorance
Hasty Generalization
False Cause
Slippery Slope
Weak Analogy
Fallacies of Ambiguity:
Equivocation
Amphibole
Fallacies of Grammatical Analogy:
Composition
Division
1. Appeal to Force (ad Baculum … appeal to the stick):
Supporting or avoiding a conclusion by threats
Worst case: when debates get derailed by jeering or
“shouting down” an arguer.
“I think we should choose xBox over Playstation
because its online multiplayer stuff is better.”
“How about I stomp your guts out? How would that
be?”
Committing Appeal to Force is less an error in
reasoning, more a bullying tactic. Either way, the
response is irrelevant to the quality of the argument
or idea.
2. Appeal to Pity (Argumentum ad
Misericordiam):
“I’m afraid going 70 in a 25mph zone
means you deserve this ticket, Ms.
Garcia.”
“No, Judge, I have three kids, late bills,
and work two jobs … I can’t deserve
this speeding ticket!”
Is the sorry state of the arguer logically
relevant to deserving the ticket?
Might the judge considering it in
sentencing?
3. Appeal to the People (Argumentum ad Populum):
Ad Populum has the form:
X is popular
X is true
Direct Approach: appeal directly to the crowd of
people … use emotive language to create mob
mentality support for a conclusion. Political
speeches?
Indirect Approach: appeal to indirectly to the crowd by
appealing directly to individuals and their
relationship to the crowd … also called a
“Bandwagon Argument”:
“Come on … everyone in this class smokes crack ... you
should take a hit!”
Individual
crowd
4. Argument to the Person (Argumentum ad Hominem): Attacking the
arguer instead of their argument.
Famous response to an ad hominem attack:
“I may be the devil’s brother,
but you still haven’t answered my argument.”
3 Kinds of ad Hominem arguments:
Abusive ad Hominem:
“I believe murderers should die for the sake of their victim’s family.”
“Only a stupid jerk-face would want anyone to die!”
…does the speaker being a jerk have anything to do with whether capital
punishment is justified based on concern for the victim’s family?
Circumstantial ad Hominem:
“I believe murderers should die for the sake of the
victim’s family.”
“Well, since your cousin was murdered, it isn’t hard to
see why you feel that way.”
Tu Quoque (you too):
“I believe murderers should die for the sake of the
victim’s family.”
“Well, I recall you defending your Uncle when he was
convicted … you weren’t suggesting he die for the
family of the guy he shot!”
5. Accident: (Misapplying
a Rule):
“Yes I told the axe
murderer where the
little girl was! … if you
check your bible, you’ll
find Thou Shalt Not Lie”
6. Straw Man (Straw Position):
Famous quote:
“If the defendant be a
man of straw,
who is to pay the penalty?”
Distorting your opponent’s view or position by
exaggerating or diminishing it, then attacking the
distorted position rather than the one the opponent
holds.
Universal health care?! Well that’s just plain, old-fashioned
Communism! (exaggeration)
Intelligent Design? Well, that’s just plain old churchy
creationism! (diminishment)
7. Missing the Point:
“So, you say Bill punched Bob in the nose? All
right, better get Bob straight to the emergency
room!”
Sometimes MtP is jumping to a distant conclusion.
Sometimes MtP is just missing the point.
“That’s a priceless Steinway!”
“Not anymore.”
http://www.youtube.com/watch?v=LwtIKdCWXls
“If you’re not out of here in 5 seconds…!”
“Ah, I could easily be out of here in three!”
8. Red Herring:
Leading listeners off track with a
related, enticing or distracting
line of thought.
“I don’t think God exists. To me,
there’s just too much evil in the
world to believe that.”
“Ah. Yes, evil is bad. But the best
way to handle it, if it upsets you,
is to seek out a therapist, or
perhaps pastoral care. Therapy
has been shown to work
wonders; I don’t see why you
would avoid it … see you in
church!”
We should give that new
position to Frank
Thompson. Frank has six
hungry kids to feed, and
his wife needs an
operation to save her
eyesight.
*from Hurley’s A Concise Introduction to Logic
AF = Appeal to Force
APi = Appeal to Pity
Ape = Appeal to the People
aH = ad Hominem
A = Accident
SM = Straw Man
MP = Missing the Point
RH = Red Herring
NF = No Fallacy
Professor Pearson’s
arguments in favor of the
theory of evolution should
be discounted. Pearson is a
cocaine-snorting sex
pervert and, according to
some reports, a member of
the communist party.
*from Hurley’s A Concise Introduction to Logic
AF = Appeal to Force
APi = Appeal to Pity
Ape = Appeal to the People
aH = ad Hominem
A = Accident
SM = Straw Man
MP = Missing the Point
RH = Red Herring
NF = No Fallacy
Some of you oppose the
appointment of David Cole as
new sales manager. Upon
further consideration, I am
sure you will find him suitable
for the job. If not confirmed, it
may be necessary to make
severe personnel cutbacks in
your department.
*from Hurley’s A Concise Introduction to Logic
AF = Appeal to Force
APi = Appeal to Pity
Ape = Appeal to the People
aH = ad Hominem
A = Accident
SM = Straw Man
MP = Missing the Point
RH = Red Herring
NF = No Fallacy
You should read Irving
Stone’s latest novel right
away. It has sold over a
million copies, and
nearly everyone in the
Manhattan cocktail
circuit is talking about it.
*from Hurley’s A Concise Introduction to Logic
AF = Appeal to Force
APi = Appeal to Pity
Ape = Appeal to the People
aH = ad Hominem
A = Accident
SM = Straw Man
MP = Missing the Point
RH = Red Herring
NF = No Fallacy
Animal rights activists say that
animals are abused in
biomedical research labs. But
consider this: Pets are abused
by their owners every day.
Probably 25 percent of pet
owners should never get near
animals. Some cases of abuse
are enough to make you sick!
*from Hurley’s A Concise Introduction to Logic
AF = Appeal to Force
APi = Appeal to Pity
Ape = Appeal to the People
aH = ad Hominem
A = Accident
SM = Straw Man
MP = Missing the Point
RH = Red Herring
NF = No Fallacy
Actress Andie MacDowell says
that it’s healthy to drink
milk. But the dairy industry
pays MacDowell thousands
of dollars to make these
ads. Therefore, we shouldn’t
take her testimonials too
seriously.
*from Hurley’s A Concise Introduction to Logic
AF = Appeal to Force
APi = Appeal to Pity
Ape = Appeal to the People
aH = ad Hominem
A = Accident
SM = Straw Man
MP = Missing the Point
RH = Red Herring
NF = No Fallacy
Dr. Morrison has argued that
smoking is responsible for the
majority of health problems in
this country and that every
smoker concerned about his or
her health should quit.
Unfortunately, however, we must
consign Dr. Morrison’s argument
to the trash bin. Only yesterday I
saw none other than Dr. Morrison
himself smoking a cigar.
*from Hurley’s A Concise Introduction to Logic
AF = Appeal to Force
APi = Appeal to Pity
Ape = Appeal to the People
aH = ad Hominem
A = Accident
SM = Straw Man
MP = Missing the Point
RH = Red Herring
NF = No Fallacy
9. Appeal to Unqualified Authority (ad
Verecundiam):
“My Econ professor said to never scold my dog, so,
now I’m a 100% positive feedback dog trainer.”
A PhD in Economics doesn’t imply dog training skill.
2 things:
1. Perhaps the Econ professor is a dog training
expert … but that has to be shown.
1. In some areas, no one is an expert: famously,
▪
▪
▪
politics,
morals, and
religion
10. Appeal to Ignorance (ad Ignorantiam):
Arguing from a lack of knowledge:
No one has proven X true, (or false)
X is false (or true)
As in…
“No one has proven God exists.”
“Is that so?”
“Yes! So, God does not exist!”
“No one as proven God doesn’t exist.”
“Is that so?”
“Yes! So, God exists!”
Appeal to Ignorance, cont.
Exceptions (below are good arguments (pretty
good)):
“Guy’s innocent.”
“Says who?”
“Well, he hasn’t been proven guilty, so he is
innocent.”
“There is no crocodile in the hall.”
“Says who?”
“Well, no one has proven there’s a crocodile in the
hall, so there isn’t.”
11. Hasty Generalization (Converse Accident):
Taking a small sample, and inferring from it all or
most of that kind are the same.
“My cabbie in New York City was surly, so, all
cabbies in NYC are surly.”
Exceptions:
1.
“This Root Beer, Roundy’s, is blah, so all
Roundy’s Root Beer is blah.”
2. “This Pit Bull (Rottweiler, Tarantula, Python,
etc.) is dangerous, so, all Pit Bulls (Rottweilers,
Tarantulas, Pythons, etc.) are dangerous.”
Two more things regarding the logic of danger (#2):
1.
When people say Pit Bulls, for instance, are dangerous, they plainly don’t
mean to include dead ones, very old ones, very young ones. Their statement
is perhaps elliptical for, “these healthy adult dogs can kill you and animals
are unpredictable. Be on guard!” You must decide if a statement is straightforward or elliptical based on context, knowledge of the speaker, or by
asking, if possible.
1.
Risk assessment logic: Risk assessments have 2 parts:
▪
▪
probability and,
severity.
Some things have very low probabilities of harm, but are dangerous because of
high severity. Commonly believed dangerous things:
▪
▪
▪
▪
▪
your weird looking neighbor,
flying in a commercial jet,
driving a car without a seatbelt,
playing just one round of Russian Roulette,
hitchhiking.
All have very low probabilities of harm. How then are they dangerous?
12. False Cause (3 Kinds)
1. False Cause: Post Hoc:
Post hoc, ergo, propter hoc
After this, therefore, because of this
“Ever since Betty showed up it’s been one thing after the other, car breaks
down, dog dies, TV on the fritz! Clearly, Betty is bad news!”
Post Hoc
“Right about the time Obama took office the economy really took a dive. I
guess we know that guy is bad for business!”
“While Reagan was taking office Iran freed the hostages. Plain to see he knew
how to take care of business!”
2. False Cause: Mere Contributive Cause (oversimplified
cause)
A Contributive Cause: one cause that is insufficient, by itself,
to produce the effect in question, but that contributes to
producing the effect.
“Edgar hung himself while listening to Suicide Solution by
Ozzy Osbourne … Ozzy should go to jail for causing his
suicide.”
How might you, as a defense attorney, using the notion of a
contributive cause, argue that this conclusion is
fallacious?
3. False Cause: Confused Causal Chains
Suppose we conclude that a dog was barking because
someone broke into its house: an intruder (X) caused
the dog to bark (Y), X caused Y … couldn’t it be …
Y caused X (someone intruded because the dog was
barking)?
Y caused a fire Z, which caused X (dog barking caused
someone to start a fire, and the fire made someone
break into the house)?
X had nothing to do with Y (the dog was barking at a
mouse; intruder broke in to steal a TV)?
Others?
13. Slippery Slope:
“If we allow gay marriage, how do we keep
from allowing




polygamy, and then
polyamory, then
sibling and parent marriage, then
pet marriage?
We will slide down the slope into chaos!”
Show the slope really is slippery:



history
statistics
motives
Slippery Slope, cont.
Throwing sand on a slippery slope:
Cite the differences between the case at
hand the next step in the slope, or at
each step … try to show, for
instance, that


jealousy makes polygamous marriages
unstable, or that
rich men getting 20 wives harms society
by shrinking the family opportunities of
poor men …
so, we surely won’t slide down the
slope?
14. Weak Analogy:
A has a, b, c, and z
B has a, b, c
So, B probably has z. (this is the form of an analogy,
not a weak analogy)
a
A
National 65 mph speed limit kills 42,000 US citizens per year,
z
and no one minds much.
a
B
The war in Iraq kills 1,000 US soldiers a year
z
So, no one should mind that much either.
To evaluate the analogy, we have to compare every relevant feature
we can think of between the national speed limit and the war in
Iraq, and see if those features strengthen or weaken the analogy.
b. Are both government policies?
c. Do they serve worthy goals?
d. Do the policies put each group at equal risk?
e. Does risk matter, or just total lives lost?
f. Can society survive without either policy?
g. Can those endangered opt out of the policy’s purview?
h. Who are the relevant dead of each policy?
i. Are injuries equally bad?
j. So on…
If you give Jane a cookie, she’ll want a glass of milk.
Then, she won’t be hungry for her supper!
AUA = Appeal to Authority
AI = Appeal to Ignorance
HG = Hasty Generalization
FC = False Cause
SS = Slippery Slope
WA = Weak Analogy
NF = No Fallacy
*from Hurley’s A Concise Introduction to Logic
Don’t listen to Rush Limbaugh. After Bob started
listening, he developed an ulcer.
AUA = Appeal to Authority
AI = Appeal to Ignorance
HG = Hasty Generalization
FC = False Cause
SS = Slippery Slope
WA = Weak Analogy
NF = No Fallacy
*from Hurley’s A Concise Introduction to Logic
Ellen is a mean drunk. I wouldn’t invite her to your
kegger, if I were you.
AUA = Appeal to Authority
AI = Appeal to Ignorance
HG = Hasty Generalization
FC = False Cause
SS = Slippery Slope
WA = Weak Analogy
NF = No Fallacy
No one would buy a pair of shoes without trying them
on. Why should anyone be expected to get married
without first having sex?
AUA = Appeal to Authority
AI = Appeal to Ignorance
HG = Hasty Generalization
FC = False Cause
SS = Slippery Slope
WA = Weak Analogy
NF = No Fallacy
*from Hurley’s A Concise Introduction to Logic
There are more churches in
New York City than in any
other city in the nation, and
more crimes committed in
New York City than anywhere
else. So, if we are to
eliminate crime, we must
abolish churches.
*from Hurley’s A Concise Introduction to Logic
AUA = Appeal to Authority
AI = Appeal to Ignorance
HG = Hasty Generalization
FC = False Cause
SS = Slippery Slope
WA = Weak Analogy
NF = No Fallacy
Probably no life exists on Venus. Teams of scientists
have conducted exhaustive studies on the planet’s
surface and atmosphere, and no living organisms
have been found.
AUA = Appeal to Authority
AI = Appeal to Ignorance
HG = Hasty Generalization
FC = False Cause
SS = Slippery Slope
WA = Weak Analogy
NF = No Fallacy
*from Hurley’s A Concise Introduction to Logic
We don’t dare let animal rights
activists get their foot in the door.
If they sell us on the idea that dogs,
cats, and dolphins have rights, next
it will be chickens and cows. Next,
it will be worms and insects. This
will lead to the decimation of our
agricultural industry. The starvation
of the human race will follow close
behind.
*from Hurley’s A Concise Introduction to Logic
AUA = Appeal to Authority
AI = Appeal to Ignorance
HG = Hasty Generalization
FC = False Cause
SS = Slippery Slope
WA = Weak Analogy
NF = No Fallacy