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 based
  on reasons where the reasons are better known
  than the conclusion.
• Explanations are the assertion of reasons based
  on a conclusion that is better known than those
  reasons.

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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 experience is most important in choosing
  our next librarian.
• Why dont I just throw you on the ground now?
  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.
• All Fallacies from Hurleys A Concise
  Introduction to Logic

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Fallacies of Relevance, cont.

• 2. Appeal to Pity (Argumentum ad Misericordiam)
• You admit going 70 in a 35mph zone?
• Yes, but 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
  ... 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 total jerk would want anyone to die!
• whether someone is a jerk or not has nothing to
  do with whether capital punishment is justified
  based on wishes of the victims family, so the
  response is irrelevant.

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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 (sometimes called Extension)
• 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!

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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!
• A warranted conclusion would be to ask if Bob is
  okay.
• Missing the Point is a catchall for fallacies
  of relevance that dont fit elsewhere.

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Fallacies of Relevance, cont.

• 8. Red Herring
• Leading listeners off track with a related,
  enticing alternative argument.
• 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, it 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.

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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.

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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.

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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.

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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!

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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.

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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.

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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.
• Note
• 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
• (hence the prohibition on discussing them at
  dinner).

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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)
• God does not exist.
• Says who?
• Well, no one has proven God exists, so he
  doesnt.
• God exists.
• Says who?
• Well, no one as proven God doesnt exist, so he
  does.

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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 is dangerous, so, Pit Bulls are
  dangerous.

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Fallacies of Weak Induction, cont.

• Two more things regarding 2
• When people say Pit Bulls are dangerous, they
  dont mean to include dead ones, very old ones,
  very young ones. They just mean, these healthy
  adult dogs can really bite!
• Even if statistically it doesnt follow that all
  healthy adult Pit Bulls are dangerous, the cost
  of guessing wrong about a particular Pit Bull can
  be enormous, making it wise to believe any
  healthy adult Pit Bull you dont know is a threat.

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Fallacies of Weak Induction, cont.

• 12. False Cause (Post Hoc Ergo Propter Hoc
  After This therefore because of this)
• The toast popped up when I turned on my phone
  so, I can make toast with my phone!
• Edgar hung himself after listening to Suicide
  Solution by Ozzy Osbourne Ozzy should probably
  go to jail or be fined for assisted suicide.

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Fallacies of Weak Induction, cont.

• False Cause Contributive Cause?
• While Ozzys music might have contributed to
  someones suicide, note that it may have been
  just one of a number of causes that worked
  together to cause the suicide.
• A Contributive Cause one cause that is
  insufficient, by itself, to produce the effect in
  question, but that contributes to producing the
  effect. You are a contributive cause when you
  lend a hand pushing a car out of the snow.

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Fallacies of Weak Induction, cont.

• 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 why
  not let people marry their pets? We will slide
  down the slope into chaos!
• Showing the slope really is slippery evidence
  from history, researching statistics (how many
  people love their pets that much?), plausibility,
  motives (what reasons might move folks down the
  slope?)

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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?
• Can society do without them?
• Do those endangered opt out of the policys
  purview?
• Do the death tolls include the relevant people?
• Are injuries equivalently 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!

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Quick Quiz

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

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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?

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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.

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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.

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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.