Testimonial knowledge Lecture 6

1
Testimonial knowledgeLecture 6

• Ben Bayer
• Philosophy 102 Logic and Reasoning

2
Overview

• The importance of testimony
• Background knowledge and the relevance of
  testimony
• Reliability requirements
• Veracity requirements
• Corroboration

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The importance of testimony

• Example What is the difference between these two
  arguments?
• My doctor is an important authority, and he says
  the Earth is flat. So the earth must be flat.
• My doctor is an important authority in his
  field, and he says that I may have a heart
  condition. So I probably have a heart condition.
• The doctor is a relevant authority on the second
  topic, but not the first

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The importance of testimony

• We rely on testimony to know all kinds of things
• About our health (if were not doctors)
• About current events (if were not reporters)
• About geography (if we havent been to distant
  countries)
• About history (if we didnt live a long time ago)
• About science (if we didnt do experiments
  ourselves)
• And much more

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The importance of testimony

• Testimony is a report by someone in a position to
  observe or qualified to infer some fact, to
  someone who is not.
• This is an issue wider than courtroom testimony.
• Much reliance on testimony is necessary most
  dont have time/expertise to verify everything on
  own
• Problem is testimony then based on a
  subjectivist fallacy, or faith (belief without
  evidence)?
• Do we use evidence in accepting testimony?
• We accept much testimony automatically do we
  have time to consider evidence about it?

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Background knowledge and the relevance of
testimony

• Solution the evidence behind testimony is held
  as background knowledge
• Background knowledge is a set of conclusions for
  which evidence has already been gathered, and
  which is taken for granted while acquiring new
  knowledge.
• If we can describe this background knowledge, we
  will know why reliable testimony is neither faith
  nor the appeal to irrelevant authority.

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Background knowledge and the relevance of
testimony

• Pieces of background knowledge supporting the
  general reliability of simple testimony
• We know that other people have successfully
  reported simple facts that we could verify for
  ourselves
• Example A mother tells a child not to touch a
  stove
• Analogy to calibrating a telescope
• We know that other people have sense organs and
  language like we do, and so are capable of
  remembering facts like we are
• Analogy to knowledge of the mechanism of the
  telescope
• We know we ourselves can make inferences based on
  privileged knowledge, assume others (experts) are
  the same.

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Background knowledge and the relevance of
testimony

• Example of background knowledge behind a new
  piece of testimony

We can know thingsand report them reliably.
Other people are likeus mentally.
Mom has predictedsafety before.
Human beings canreport their knowledgeto us.
Mom says its not safe tocross the street.
Mom knows what is safe.
Its not safe to cross thestreet.
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Background knowledge and the relevance of
testimony

• Problem Were not always in a position to
  calibrate people
• Solution could accept someones testimony if his
  reliability supported by other testimony (from
  someone who could calibrate the doctor)
• This works only if the second piece of testimony
  is from someone weve already calibrated (like
  parents or friends)
• Otherwise circularity!
• Problem Even if some testimony is reliable, not
  all of it is how tell the difference?

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Reliability requirements

• Reliability is the degree to which testimony is
  likely to yield accurate reports.
• Authorities are relevant only when their
  testimony is reliable.
• The reliability of testimony varies depending on
  subject matter.
• Everyone is an expert at reporting observations
  about normal middle-sized objects and events
  under normal conditions
• Only some are experts at reporting observations
  requiring specialized inferences

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Reliability requirements

• Failures of reliability
• May even fail to identify ordinary objects and
  events if circumstances are not normal
• May be at wrong time/place to make accurate
  judgment
• May have impaired senses or faculties

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Reliability requirements

• Examples of ordinary reliability failure
• Claiming to identify an assailant by the
  moonlight, when Lincolns almanac says the moon
  was just setting.
• Claiming to identify a person from a distance,
  without wearing ones glasses.
• Claiming to identify someone while under the
  influence of alcohol.

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Reliability requirements

• Failures of reliability
• May even fail to identify ordinary objects and
  events if circumstances are not normal
• May be at wrong time/place to make accurate
  judgment
• May have impaired senses or faculties
• May fail to have level of expertise knowledge
  necessary for making specialized inferences

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Reliability requirements

• Examples of expert reliability failure
• Claiming to diagnose the cause of some death,
  while lacking medical expertise.
• Claiming to know the cause of the World Trade
  Centers collapse, while lacking engineering
  expertise.
• Claiming to know the cause of global warming,
  while lacking scientific expertise.

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Reliability requirements

• Group exercise
• Determine whether these reports are being given
  by experts of the proper kind
• A zoologist reports I saw a black cat cross my
  path.
• A man of unknown background reports I saw the
  suspect shoot Mr. Smith, having maliciously
  planned to kill him.
• An economist reports Our tax policy is
  completely immoral, because the top 1 of earners
  have the biggest tax cuts.

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Reliability requirements

• Problem how does a layman identify an expert?
• Cannot simply take the experts word that he is
  an expert.
• This would be circular reasoning!
• Cant necessarily just look to other experts in
  the same field
• This would also be circular would need to know
  they were experts in order to trust them
• Solution
• Can judge by their ability to explain to you what
  you do understand

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Reliability requirements

• Example of expert identification from My Cousin
  Vinnie
• D.A. Jim Trotter Now, Ms. Vito, being an expert
  on general automotive knowledge, can you tell
  me... what would the correct ignition timing be
  on a 1955 Bel Air Chevrolet, with a 327
  cubic-inch engine and a four-barrel carburetor?
  Mona Lisa Vito That's a bullshit question.
• D.A. Jim Trotter Does that mean that you can't
  answer it?
• Mona Lisa Vito It's a bullshit question, it's
  impossible to answer.
• D.A. Jim Trotter Impossible because you don't
  know the answer!
• Mona Lisa Vito Nobody could answer that
  question!
• D.A. Jim Trotter Your Honor, I move to
  disqualify Ms. Vito as an expert witness!
• Judge Chamberlain Haller Can you answer the
  question?
• Mona Lisa Vito No, it is a trick question!
• Judge Chamberlain Haller Why is it a trick
  question?
• Vinny Gambini Watch this.
• Mona Lisa Vito 'Cause Chevy didn't make a 327
  in '55, the 327 didn't come out till '63. And it
  wasn't offered in the Bel Air with a four-barrel
  carb till '64. However, in 1964, the correct
  ignition timing would be four degrees before
  top-dead-center.
• D.A. Jim Trotter Well... uh... she's
  acceptable, Your Honor.

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Reliability requirements

• Problem how does a layman identify an expert?
• Cannot simply take the experts word that he is
  an expert.
• This would be circular reasoning!
• Cant necessarily just look to other experts in
  the same field
• This would also be circular would need to know
  they were experts in order to trust them
• Solution
• Can judge by their ability to explain to you what
  you do understand
• Can depend on experts you can calibrate who
  have a greater ability to calibrate more
  expertise

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Reliability requirements

• More failures of reliability
• May involve hearsay
• Hearsay is a statement, other than one made by
  the declarant while testifyingoffered in
  evidence to prove the truth of the matter
  asserted
• In other words, hearsay is testimony about
  testimony, second-hand testimony

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Reliability requirements

• Example of direct testimony vs. hearsay
  (secondhand testimony

I saw him commit the burglary
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Reliability requirements

• Example of direct testimony vs. hearsay
  (secondhand testimony

I saw him commit the burglary.
She told me she saw him commit the burglary.
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Reliability requirements

• More failures of reliability
• May involve hearsay
• Hearsay is a statement, other than one made by
  the declarant while testifyingoffered in
  evidence to prove the truth of the matter
  asserted
• In other words, hearsay is testimony about
  testimony, second-hand testimony
• Hearsay is unreliable because
• Cannot necessarily verify reliability of the
  original testifier, only that of the secondary
  testifier.
• Cannot necessarily determine meaning of original
  testimony
• Exceptions excited utterances, statements of
  observation, state of mind, statements against
  interest, etc.

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Reliability requirements

• Examples of hearsay (later shown to be false)
• Rumors after Hurricane Katrina about rapes and
  murders at convention center, sharks swimming in
  the streets, attacks by gangs. (LA Times,
  9/27/05)
• Rumors during 9/11 about bombs on bridges,
  attacks on Camp David, the State Department, etc.
  (Washington Post, 9/16/01)
• During times of confusion, rumors spread as
  normal chains of communication break down and
  people fear the worst.

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Reliability requirements

• More examples of false hearsay
• Men think about sex every seven seconds.
• (Actually 54 think about it every day, 43 a
  few times a month, 4 less than once a month
  (Kinsey Institute)
• We use only 10 of our brains.
• The average person swallows eight spiders a
  year.
• These urban legends debunked courtesy of
  www.snopes.com

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Reliability requirements

• More examples of hearsay debunked by Snopes
• A student whose roommate commits suicide
  automatically receives a 4.0.
• A munchkin can be seen hanging himself during a
  scene of The Wizard of Oz.
• Puff the Magic Dragon is a song about
  marijuana.

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Reliability requirements

• Testing the Wikipedia (the encyclopedia anyone
  can edit)
• Nature sent sample entries to experts (2005)
• found average Wikipedia article to contain four
  inaccuracies, Britannica only three
• 162 factual errors in Wikipedia samples, 123 in
  Brittanica
• each encyclopedia contained only four serous
  misrepresentations
• Britannicas reply (The Register, March 2006)
• Nature sent misleading fragments of their
  articles, like from the childrens version
• Nature stitched different pieces of Britannica
  articles together
• In general be wary of Wikipedia! No way of
  assessing if its written by experts!

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Veracity requirements

• A reliable testifier might choose not to tell the
  truth
• Veracity is the degree of a persons commitment
  to tell the truth.
• Judgments of a testifiers veracity undermined
  by
• Discrepancies in a story suggesting falsification

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Veracity requirements

• Example of fabrication from Wikipedia

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Veracity requirements

• Group exercise
• Analyze the following email forward and attached
  image for veracity
• Is there anything funny about the picture? The
  story?

This was taken by the crew on board the Columbia
during its last mission. This photo was
taken via satellite, on a cloudless day. The
picture is of Europe and Africa when the sun is
setting. Half of the picture is in night. The
bright dots you see are the cities lights. The
top part of Africa is the Sahara Desert. Note
how the lights are already on in Holland, Paris,
and Barcelona, and how it's still daylight in
London, Lisbon, and Madrid.
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Veracity requirements

• A reliable testifier might choose not to tell the
  truth
• Veracity is the degree of a persons commitment
  to tell the truth.
• Judgments of a testifiers veracity undermined
  by
• Discrepancies in a story suggesting falsification
• A testifiers reputation for dishonesty or bias
• But note that evidence of bias is not provided
  simply by motive

31
Veracity requirements

• Examples of types of expert testimony that may be
  biased or not
• A university researcher publishes a study
  alleging that oil companies pollute the
  environment.
• A think tank researcher, funded by the oil
  industry, publishes a paper refuting that study.
• Bias is a tendency towards non-objective
  examination of the facts.
• Both selflessness and self-interest are
  compatible with bias!

32
Veracity requirements

• A reliable testifier might choose not to tell the
  truth
• Veracity is the degree of a persons commitment
  to tell the truth.
• Judgments of a testifiers veracity undermined
  by
• Discrepancies in a story suggesting falsification
• A testifiers reputation for dishonesty or bias
• But note that evidence of bias is not provided
  simply by motive
• A testifiers generally poor moral character
• Testimony may be dismissed by attacking
  character, but arguments may not be dismissed in
  same way
• The ad hominem fallacy is attacking an argument
  by attacking the arguer rather than its logic.

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Veracity requirements

• Examples of the ad hominem fallacy
• A I think all men have rights, so slavery is
  unjustified.
• B Dont pay attention to Mr. As argument
  against slavery. Hes a known philanderer!
• Kerry I have a plan. Here are reasons to adopt
  it.
• Bush Kerry is a flip-flopper. First he plans to
  do one thing, then another.
• Pro-war We should go to war because it will
  protect us from terrorism.
• Anti-war Youre a chickenhawk! I dont see you
  going off to fight!

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Veracity requirements

• Group exercise
• Discuss whether these are examples of the valid
  dismissal of the veracity of testimony, or the
  invalid use of the ad hominem fallacy, or
  something else
• Politician 1 Here is evidence that my opponent
  takes bribes.
• Politician 2 Dont listen to him. He takes
  bribes, too!
• Politician 1 If elected, I promise to cut
  taxes.
• Politician 2 Dont listen to him. Hes broken
  many campaign promises before.

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Corroboration

• Corroboration is the strengthening of one
  persons testimony by showing that it agrees with
  other testimony or independent facts.
• Can corroborate by
• Finding other testifiers who agree with it
• Example Further eyewitnesses.
• Example A second medical opinion.

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Corroboration

• Example of testimony that does not corroborate
  well (an perennial email forward)
• Why wouldnt we have heard news about this from
  major media outlets?

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mail to retrieve your messages. To prevent
this, call 888-382-1222 from your cell phone.
This is the national DO NOT CALL list it takes
only a minute to register your cell phone number
and it blocks most telemarketers calls for five
years. In case you have friends other than
me, pass this on to them.
37
Corroboration

• Corroboration is the strengthening of one
  persons testimony by showing that it agrees with
  other testimony or independent facts.
• Can corroborate by
• Finding other testifiers who agree with it
• Example Further eyewitnesses.
• Example A second medical opinion.
• Making sure it fits with other better
  known-facts, not like
• I have squared the circle!
• I have invented a perpetual motion machine!
• I just witnessed a miracle!

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Introduction to deductionLecture 22

• Ben Bayer
• Philosophy 102 Logic and Reasoning

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Overview

• Two functions of inference (and associated forms)
  
• Why we need deduction
• Some famous deductions
• Two types of deductive inference

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Two functions of inference (and associated forms)

• Acquiring new generalized knowledge from
  observation
• Induction is a form of reasoning that moves from
  observations to a conclusion wider in
  informational content than the premises.
• Applying existing generalized knowledge to new
  cases
• This is called deduction or deductive
  reasoning
• Deduction is a form of reasoning that unpacks
  implications of existing knowledge, drawing
  conclusions no wider in content than the
  premises.

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Two functions of inference (and associated forms)

• All Greeks are human beings.
• All human beings are mortal.
• All Greeks are mortal.

Mortals
Human Beings
Greeks
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Why we need deduction

• We need deduction to apply our knowledge to new
  situations
• In particular, we need a step-by-step method
  because the implications of our knowledge are not
  always easily grasped

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Why we need deduction

• Some deductive arguments identify relations easy
  to see in reality itself
• Aristotle is taller than Plato.
• Plato is taller than Socrates.
• Aristotle is taller than Socrates.

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Why we need deduction

• Other deductive arguments identify relations that
  are not easy to see at all!
• AE AB
• AF AC
• ?BAF ?BAC ?CAF ?CAB ?BAE ?CAE
• Therefore, area of ?ABF area of ? AEC
• But the area of ?ABF ½ AC2
• And the area of ?AEC ½ area of AELM
• So ½ AC2 ½ area of AELM
• And AC2 area of AELM
• Similarly BC2 area of BMLD
• But AELM BMLD square on the hypotenuse.
• Therefore, the square on the hypotenuse AC2
  BC2

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Why we need deduction

• In general, deduction works to grasp bigger
  relationships by piecing together smaller
  relationships step-by-step
• Solve this riddle Brothers and sisters have I
  none, but this mans father is my fathers son.
• This mans father is my fathers son.
• My fathers son is me or my brothers.
• Brothers and sisters have I none.
• My fathers son is me.
• This mans father is me.
• I am the father of this man.
• This man is my son.

46
Some famous deductions

• Deduction is a form of inference, because the
  ability to unpack implications of our existing
  knowledge can yield surprising new information

47
Some famous deductions

• Eratosthenes trigonometric proof of the
  circumference of the Earth (3rd century BC)
• The angle of the shadow at noon at Alexandria is
  7.2 degrees.
• Alternating interior angles are equal.
• Therefore the angle between Alexandria and Syene
  is 7.2 degrees.
• The distance from Alexandria to Syene is 500
  miles.
• But (Circumference of earth/500 miles)360/7.2
• Therefore Circumference of earth 25,000 miles.
• But Circumference/pi Diameter, 25,000/3.14
  8,000 miles.
• Therefore diameter of earth is 8,000 miles.
• Using this, can calculate size of moons diameter
  (through eclipse shadows) and distance to the
  moon.

48
Some famous deductions

• Aristarchus trigonometric calculation of the
  distance to the sun (3rd century BC)
• The angle between the sun and the moonduring a
  half moon is 87 degrees.
• Cos 87 moon distance/sun distance
• Sun distance/moon distance 1/cos 87 19
• Therefore, the suns distance from the earthis
  19 times its distance to the moon.
• With knowledge of distance to moon, can calculate
  actual distance to sun

49
Why we need deduction

• Maxwells (1864) prediction of the existence and
  speed of EM waves
• Maxwell formulated an equation showing a change
  in an electric field would create a magnetic
  field.
• Since a changing magnetic field was already known
  to create an electric field, this implied there
  should be an electromagnetic wave!
• Maxwell even predicted the speed of the EM wave,
  and realized it was also the previously
  calculated speed of light.

50
Two types of inference

• Well study these two kinds of deductive
  inference
• Categorical syllogisms
• All Greeks are human beings.
• All human beings are mortal.
• All Greeks are mortal.
• Hypothetical syllogisms
• If something is Greek it is human.
• If something is human it is mortal.
• If something is Greek it is mortal.