Richard L Epstein

by Critical Thinking (3rd Edition) (pdf)

  To give you a better idea of what you're expected to do, I've included

  Manuel's argument on a different issue on the following page.

  78

  Writing Lesson 4 79

  Manuel Luis Andrade y Castillo de Pocas

  Critical Thinking

  Section 2

  Writing Lesson 4

  Issue: The chance of contracting AIDS through sexual contact can be

  significantly reduced by using condoms.

  Definition: "AIDS" means "Acquired Immunodeficiency Syndrome"

  "significantly reduced" means by more than 50%

  "using condoms" means using a condom in sexual intercourse rather

  than having unprotected sex

  Premises:

  • AIDS can only be contracted by exchanging blood or semen.

  • In unprotected sex there is a chance of exchanging blood or semen.

  • Condoms are better than 90% effective in stopping blood and semen.*

  • 90% is bigger than 50%.

  • AIDS has never been known to have been contracted from sharing food,

  using a dirty toilet seat, from touching, or from breathing in the same

  room with someone who has AIDS.

  • If you want to avoid contracting AIDS you should use a condom.

  Conclusion: The chance of contracting AIDS through sexual contact can be

  significantly reduced by using condoms.

  *I'm not sure of the exact figure, but I know it's bigger than 90%.

  Good. Your argument is indeed valid. (But it could easily be better, You don't need

  "only" in A, which is what makes me uneasy in accepting that claim. And without a

  reference to medical literature, I'm not going to accept B. But you don't need it. You

  can delete it and your argument is just as good.

  And the last claim, C, is really irrelevant— delete it. This isn't an editorial:

  you're not trying to convince someone to do something;you're trying to convince them

  an objective claim is true.

  Cartoon Writing Lesson B

  Here is a chance to reason as you might in your everyday life.

  For each cartoon write the best argument you can that has as its conclusion

  the claim that accompanies the cartoon. List only the premises and conclusion.

  If you believe the best argument is only weak, explain why. Refer back to Cartoon

  Writing Lesson A on p. 55 for suggestions about how to do this lesson.

  Remember that with subjective claims, you may need to have a premise that

  links actions to thoughts, beliefs, or feelings.

  To give you a better idea of what you're expected to do, I've included Maria's

  writing lesson for a different cartoon below the ones you're to do.

  Spot ran away.

  Dr. E shaved.

  80

  Cartoon Writing Lesson B 81

  3.

  The dog is trying to catch the Frisbee.

  The mother is scolding her child for breaking the flower pot.

  Spot is afraid of being punished.

  Suzy hit Puff with the car.

  82 Cartoon Writing Lesson B

  Name Maria Schwartz Rodriguez Section 6.

  In New Mexico cars are required to have only one license plate, in the rear.

  1. Some of the cars don't have license plates in the front.

  2. All of the cars have license plates in the back.

  3. So probably the rear license plate is required, and no front plate is required in

  New Mexico, since it is pretty unlikely all the front plates just fell off.

  You've only proved part of the conclusion with your argument. How do you know

  these are New Mexico cars?

  first, this is a restaurant parking lot, so these, are normal cars, not cars for sale in

  a used car lot, where of course many of them wouldn't have license plates.

  Second, the restaurant is advertising New Mexico's best chile, and so it must be

  in New Mexico. It would be absurd for a restaurant to advertise like that in another

  state.

  'Third, if it's in New Mexico, it's likely that most of the cars there are from 'Hew

  Mexico— not certain, but likely.

  Now you can use the argument you gave to get the conclusion. 'But you could

  have gotten a much stronger argument using the following general claim:

  It would be extremely unlikely for three drivers at the same time and place

  to have lost their front plates and to risk a serious penalty for not having a

  front plate.

  Overall, this is pretty good, you're only using what you see, not making up a

  story. But you're not using enough of what you see— remember to prove all of the

  conclusion. Also, it's really good how you put in theglue, the last part of #3 that

  shows how yougot from what you saw to the conclusion. But #3 is two claims, not

  one, as you recognized by using that indicator word "since." Be sure to list each claim separately so you can judge the plausibility of each and see how it links to the others.

  Is That True?

  A. Evaluating Premises 83

  B. Criteria for Accepting or Rejecting Claims

  1. Personal experience 84

  • Exercises for Sections A and B.l 86

  2. Other sources 87

  Summary: When to accept and when to reject 90

  • Exercises for Section B 91

  C. Advertising and the Internet

  Advertising 94

  The Internet 94

  • Exercises for Section C 95

  D. Common Mistakes in Evaluating Premises

  1. Arguing backwards 96

  2. Confusing possibility with plausibility 97

  3. Bad appeals to authority 97

  4. Mistaking the person for the claim 97

  5. Mistaking the person for the argument 98

  • Exercises for Section D 99

  Summary 101

  A. Evaluating Premises

  Recall the tests that an argument must pass to be good:

  There is good reason to believe the premises.

  The premises are more plausible than the conclusion.

  The argument is valid or strong.

  In the last two chapters we looked at how to evaluate whether the conclusion follows

  from the premises. Now we'll consider what is good reason to believe the premises.

  But why simply believe a premise? Shouldn't every claim be backed up with

  an argument? We can't do that. If we want a justification for every claim, we'd

  have to go on forever. We'd never get started. Sometimes when someone makes a

  claim we just have to decide if we believe it.

  83

  84 CHAPTER 5 Is That True?

  Three choices we can make about whether to believe a claim

  • Accept the claim as true.

  • Reject the claim as false.

  • Suspend judgment.

  We needn't pretend to be all wise, nor force ourselves to make judgments.

  Sometimes it's best to suspend judgment and evaluate the argument as well as we

  can. If we find that it's valid or strong, we can then worry about whether the premise

  is true. Rejecting a claim means to say that it is false.

  not believe it believe it is false

  lack of evidence evidence it is false

  B. Criteria for Accepting or Rejecting Claims

  There are no absolute rules for when to accept, when to reject, and when to suspend

  judgment about a claim. It's a skill, weighing up the criteria in this section, as

  presented in their order of importance.

  1. Personal experience

  What would you think of an adult who never trusted his own experience, who always />
  deferred to authority? He goes to a priest and asks him if it's daytime. He looks up

  in an atlas whether his hometown is in Nevada. He asks his wife whether the room

  they're standing in is painted white. You'd say he's crazy.

  Our most reliable source of information about the world is our own experience.

  We need to trust our own experience because that's the best we have.

  Everything else is second-hand. Should you trust your buddy, your spouse, your

  priest, your professor, the President, the dictator, when what they say contradicts

  what you know from your own experience? That way lies demagoguery, religious

  intolerance, and worse. Too often leaders have manipulated the populace: All

  Muslims want the overthrow of the West? But what about my neighbor who's

  Muslim and a city councilor? You have to forget your own experience to believe the

  Big Lie. They repeat it over and over and over again until you begin to believe it,

  even when your own experience says it isn't so.

  Oh, we get the idea. Don't trust the politicians. No. It's a lot closer to home

  than that. Every rumor, all the gossip you hear, compare it to what you know about

  the person or situation. Don't repeat it. Be rational, not part of the humming crowd.

  SECTION B Criteria for Accepting or Rejecting Claims 85

  Still, there are times we shouldn't trust our own experience. Sometimes our

  memory is not reliable. As Sgt. Carlson of the Las Vegas Police Department says,

  "Eyewitnesses are terrible. You get a gun stuck in your face and you can't remember

  anything." The police do line-ups, putting a suspect to be identified by a witness

  among other people who look a bit similar. The police have to be very careful not to

  say anything that may influence the witness, because memory is malleable.

  The state of the world around us can also affect our observations and make our

  personal experience unreliable. You could honestly say you were sure the other

  driver didn't put on a turn signal, when it was the rain and distractions that made

  you not notice.

  But even then, there are times we're right not to trust our own experience.

  You go to the circus and see a magician cut a lady in half. You saw it, so it has to

  be true. Yet you don't believe it. Why? Because it contradicts too much else you

  know about the world.

  Or stranger still: Day, after day, after day we see the sun rise in the east and set

  in the west, yet we say the sun isn't moving, the earth is. We don't accept our own

  experience because there's a long story, a theory of how the earth turns on its axis

  and revolves around the sun. And that story explains neatly and clearly so many

  other phenomena, like the seasons and the movement of stars in the skies, that we

  accept it. A convincing argument has been given for us to reject our own experience,

  and that argument builds on other experiences of ours.

  • We accept a claim if we know it is true from our own experience.

  • We reject a claim if we know it is false from our own experience.

  Exceptions

  —We have good reason to doubt our memory or our perception.

  — The claim contradicts other experiences of ours, and there is a

  good argument (theory) against the claim.

  But too often we remember what we deduced from our experience, not what we

  actually experienced. Look at Tom's cartoon writing lesson on p. 56. He said he

  saw the guy grab the purse. But he didn't see that; he inferred it.

  86

  CHAPTER 5 Is That True?

  Exercises for Sections A and B.l

  1. Why can't we require that every claim be backed up?

  2. What three choices can we make about whether to believe a claim?

  3. If the conclusion of a valid argument is false, why must one of the premises be false?

  4. Give an example of a rumor or gossip you heard in your personal life recently that

  you believed. Did you have good reason to believe it? Why?

  5. We can tell that a rumor or gossip is coming up when someone says, "Guess what I

  heard." Give five other phrases that alert us similarly.

  6. Shouldn't you trust an encyclopedia over your own experience? Explain.

  7. Give an example of a claim that someone made this week that you knew from your own

  experience was false.

  8. Give an example of a claim that you believed was true from memory, but really you

  were making a deduction from your experience.

  9. When is it reasonable for us to accept a claim that disagrees with our own experience?

  Give an example (not from the text) of a claim that it is reasonable for you to accept

  even though it seems false from your own experience.

  10. Remember the last time this class met? Answer the following about your instructor.

  a. Male or Female? f. Did he/she bring a backpack to class? Describe it.

  b. Hair color? g. Did he/she use notes?

  c. Eye color? h. Did he/she get to class early?

  d. Approximate height? i. Did he/she wear a hat?

  e. Approximate weight? j. Is he/she left-handed or right-handed?

  11. Remember the last time this class met? Answer the following about the room.

  a. How many windows? g. How many students showed up?

  b. How many doors? h. Chalkboard?

  c. How many walls? i. Lectern?

  d. Any pictures? j. Wastebasket?

  e. How high is the ceiling? k. What kind of floor (concrete, tile, linoleum, carpet)?

  f. How many chairs? 1. Did you get out of class early?

  12. Which of your answers to Exercises 10 and 11 were from actual memory and which

  were inferences?

  13. List five ways that the physical conditions around us can affect our observations.

  14. List five ways that your mental state could affect your observations.

  15. Our personal observations are no better than .

  16. What does a bad argument tell us about its conclusion?

  17. If a strong argument has one false premise and thirteen true premises, what choice

  should we make about whether to believe its conclusion?

  SECTION B Criteria for Accepting or Rejecting Claims 87

  2. Other sources

  What about claims from other sources?

  We can accept a claim made by someone we know and trust who is

  an authority on this kind of claim.

  Zoe tells Harry to stay away from the area of town around South 3rd. She's seen

  people doing drugs there and knows two people who have been held up in that

  neighbor-hood. He'll believe those premises and likely accept the conclusion that

  follows from those (and other unstated) premises. It makes sense. Zoe is reliable,

  and the claims she's making are the sort about which her knowledge would matter.

  On the other hand, your mother tells you that you should major in business so

  you can get ahead in life. Should you believe her? She can tell you about her

  friends' children. But what are the chances of getting a good job with a degree in

  business? It would be more reasonable to check with the local colleges where they

  keep records on the hiring of graduates. Don't reject her claim. Suspend judgment

  until you get more information.

  Other authorities we don't know as well are sometimes reliable, too. For

  example, the Surgeon General announces that smoking is bad for your health. She's

  got no axe to grind. She's a physician. She's in a position to su
rvey the research on

  the subject. It's reasonable to believe her.

  We can accept a claim made by a reputable authority whom we can trust

  as an expert on this kind of claim and who has no motive to mislead.

  The doctor hired by the tobacco company says there's no proof that smoking

  is addictive or causes lung cancer. Is he an expert on smoking-related diseases or a

  pediatrician? It matters in deciding whether to trust his ability to interpret the

  epidemiological data. And he has a motive to mislead, being paid by the tobacco

  companies. There's no reason to accept his claim, and some motive to reject it.

  And when the Surgeon General says that marijuana should not be legal, we

  should ask what kind of authority she is on this subject. Is she a politician? What

  kind of expertise does she have on matters of law and public policy? She's an

  authority figure, but not an expert on this kind of claim. No reason to accept her

  claim just because she said so.

  Which authorities we trust and which we disregard change from era to era. It

  was the lying by Presidents Nixon and Johnson that led many of us to distrust

  pronouncements from the government. It was the Chicago police killing the Black

  Panthers in their beds and calling it self-defense that convinced many of us not to

  88 CHAPTER 5 Is That True?

  accept what big city police say. I remember when I visited Denmark in 1965 as an

  exchange student, they asked me who I thought killed President Kennedy. I said,

  "Oswald." They asked me why I believed that. I said because the FBI said so. They

  all shook their heads in sadness, right after they stopped laughing.

  The moral is that some authorities are more trustworthy than others, even in

  their own areas of expertise. Some may have motive to mislead. The more you tell

  the truth, the more likely you are to be believed; but even one lie can ruin your

  reputation for reliability.

  What are you to do if the authorities disagree? Suspend judgment. Except that

  you don't always have that option. If you're on a jury where two ballistics experts

  disagree on whether the bullet that killed the victim came from the defendant's gun,

  what should you do? You have to make a decision. Even if you think an authority

  has the expertise to speak on a subject and has no motive to mislead, you'll still have