Informal Logic, Famous Fallacies

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Informal Logic, Famous Fallacies

• Dont Be Fooled by Bad Arguments

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First, what are 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.

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Classification of Fallacies

• Fallacies of Relevance
• Appeal to Force
• Appeal to Pity
• Appeal to the People
• Ad Hominem
• Accident
• Straw man
• Missing the Point
• Red Herring

Weak Induction Appeal to Unqualified
Authority Appeal to Ignorance Hasty
Generalization False Cause Slippery Slope Weak
Analogy
Fallacies of Ambiguity Equivocation Amphibole
Fallacies of Presumption Begging the
Question Complex Question Faulty Dilemma
Fallacies of Grammatical Analogy Composition Divi
sion
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8 Fallacies of Relevance

• 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.

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Fallacies of Relevance, cont.

• 2. Appeal to Pity (Argumentum ad Misericordiam)
• Im 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 cant deserve this speeding
  ticket!
• Is the sorry state of the arguer logically
  relevant to deserving the ticket?
• Might the judge considering it in sentencing?

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Fallacies of Relevance, cont.

• 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
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Fallacies of Relevance, cont.

• 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 devils brother,
• but you still havent answered my argument.
• 3 Kinds of ad Hominem arguments
• Abusive ad Hominem
• I believe murderers should die for the sake of
  their victims 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 victims family?

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Fallacies of Relevance, cont.

• Circumstantial ad Hominem
• I believe murderers should die for the sake of
  the victims family.
• Well, since your cousin was murdered, it isnt
  hard to see why you feel that way.
• Tu Quoque (you too)
• I believe murderers should die for the sake of
  the victims family.
• Well, I recall you defending your Uncle when he
  was convicted you werent suggesting he die for
  the family of the guy he shot!

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Fallacies of Relevance, cont.

• 5. Accident (Misapplying a Rule)
• Yes I told the axe murderer where the little
  girl was! if you check your bible, youll find
  Thou Shalt Not Lie

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Fallacies of Relevance, cont.

• 6. Straw Man (Straw Position)
• Famous quote
• If the defendant be a
• man of straw,
• who is to pay the penalty?
• Distorting your opponents view or position by
  exaggerating or diminishing it, then attacking
  the distorted position rather than the one the
  opponent holds.
• Universal health care?! Well thats just plain,
  old-fashioned Communism! (exaggeration)
• Intelligent Design? Well, thats just plain old
  churchy creationism! (diminishment)

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Fallacies of Relevance, cont.

• 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.
• Thats a priceless Steinway!
• Not anymore. http//www.youtube.com/watch?vLwtI
  KdCWXls
• If youre not out of here in 5 seconds!
• Ah, I could easily be out of here in three!

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Fallacies of Relevance, cont.

• 8. Red Herring
• Leading listeners off track with a related,
  enticing or distracting line of thought.
• I dont think God exists. To me, theres 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 dont see why you would avoid
  it see you in church!

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Quick Quiz

• 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 Hurleys A Concise Introduction to Logic
14
Quick Quiz

• Professor Pearsons 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 Hurleys A Concise Introduction to Logic
15
Quick Quiz

• 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 Hurleys A Concise Introduction to Logic
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Quick Quiz

• You should read Irving Stones latest novel right
  away. It has sold over a million copies, and
  nearly everyone in the Manhattan cocktail circuit
  is talking about it.

from Hurleys A Concise Introduction to Logic
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Quick Quiz

• 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 Hurleys A Concise Introduction to Logic
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Quick Quiz

• Actress Andie MacDowell says that its healthy to
  drink milk. But the dairy industry pays MacDowell
  thousands of dollars to make these ads.
  Therefore, we shouldnt take her testimonials too
  seriously.

from Hurleys A Concise Introduction to Logic
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Quick Quiz

• 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.
  Morrisons argument to the trash bin. Only
  yesterday I saw none other than Dr. Morrison
  himself smoking a cigar.

from Hurleys A Concise Introduction to Logic
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Fallacies of Weak Induction

• 9. Appeal to Unqualified Authority (ad
  Verecundiam)
• My Econ professor said to never scold my dog,
  so, now Im a 100 positive feedback dog
  trainer.
• A PhD in Economics doesnt imply dog training
  skill.
• 2 things
• Perhaps the Econ professor is a dog training
  expert but that has to be shown.
• In some areas, no one is an expert famously,
• politics,
• morals, and
• religion

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Fallacies of Weak Induction, cont.

• 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 doesnt exist.
• Is that so?
• Yes! So, God exists!

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Fallacies of Weak Induction, cont.

• Appeal to Ignorance, cont.
• Exceptions (below are good arguments (pretty
  good))
• Guys innocent.
• Says who?
• Well, he hasnt been proven guilty, so he is
  innocent.
• There is no crocodile in the hall.
• Says who?
• Well, no one has proven theres a crocodile in
  the hall, so there isnt.

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Fallacies of Weak Induction, cont.

• 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
• This Root Beer, Roundys, is blah, so all
  Roundys Root Beer is blah.
• This Pit Bull (Rottweiler, Tarantula, Python,
  etc.) is dangerous, so, all Pit Bulls
  (Rottweilers, Tarantulas, Pythons, etc.) are
  dangerous.

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Fallacies of Weak Induction, cont.

• Two more things regarding the logic of danger
  (2)
• When people say Pit Bulls, for instance, are
  dangerous, they plainly dont 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 straight-forward or elliptical based
  on context, knowledge of the speaker, or by
  asking, if possible.
• 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?

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Fallacies of Weak Induction, cont.

• 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 its been one thing
  after the other, car breaks down, dog dies, TV on
  the fritz! Clearly, Betty is bad news!
• 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!

Post Hoc
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Fallacies of Weak Induction, cont.

• 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?

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Fallacies of Weak Induction, cont.

• 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
  couldnt 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?

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Fallacies of Weak Induction, cont.

• 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

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Fallacies of Weak Induction, cont.

• 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 wont slide down the slope?

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Fallacies of Weak Induction, cont.

• 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)
• National 65 mph speed limit kills 42,000 US
  citizens per year,
• and no one minds much.
• The war in Iraq kills 1,000 US soldiers a year
• So, no one should mind that much either.

a
A
z
a
B
z
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Fallacies of Weak Induction, cont.

• 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.
• Are both government policies?
• Do they serve worthy goals?
• Do the policies put each group at equal risk?
• Does risk matter, or just total lives lost?
• Can society survive without either policy?
• Can those endangered opt out of the policys
  purview?
• Who are the relevant dead of each policy?
• Are injuries equally bad?
• So on

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Quick Quiz

• If you give Jane a cookie, shell want a glass of
  milk. Then, she wont be hungry for her supper!

from Hurleys A Concise Introduction to Logic
33
Quick Quiz

• Dont listen to Rush Limbaugh. After Bob started
  listening, he developed an ulcer.

from Hurleys A Concise Introduction to Logic
34
Quick Quiz

• Ellen is a mean drunk. I wouldnt invite her to
  your kegger, if I were you.

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Quick Quiz

• No one would buy a pair of shoes without trying
  them on. Why should anyone be expected to get
  married without first having sex?

from Hurleys A Concise Introduction to Logic
36
Quick Quiz

• 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 Hurleys A Concise Introduction to Logic
37
Quick Quiz

• Probably no life exists on Venus. Teams of
  scientists have conducted exhaustive studies on
  the planets surface and atmosphere, and no
  living organisms have been found.

from Hurleys A Concise Introduction to Logic
38
Quick Quiz

• We dont 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 Hurleys A Concise Introduction to Logic