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This handout is about the use of sound reasoning to reach a valid

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This handout is about the use of sound reasoning to reach a valid

READING VALID/INVALID ARGUMENTS R-11

    This handout is about the use of sound reasoning to reach a valid conclusion, and thus concerns arguments. An argument, in this sense, is not a dispute between two

    people. Rather, it means the advancing of reasons to support a conclusion. An argument consists of two parts: one or more reasons and a conclusion. The reasons are the

    evidence given to support the conclusion. The critical reader must be able to recognize when an argument is being advanced and to identify its reasons and conclusion. The reader can then evaluate the worth of the argument.

    Transition words can be useful in recognizing arguments and in identifying their reasons and conclusions.

Words and phrases that frequently signal reasons include:

     First of all in view of the fact

     Secondly as indicated by

     Because for that reason

     For example since

    Words and phrases that frequently signal conclusions include:

     Therefore it follows that

     So as a result

     Thus then

     As a result consequently

     Arguments do not always include such transition or signal words, and the signal words do not always mean an argument is being made. But signal words can be useful in making you aware of an argument and in helping you identify its reasons and conclusions.

     As you examine arguments, keep in mind that not all arguments are arranged in the same order. While a conclusion does follow logically from the reasons supporting it, it need not come at the end of the argument. Examine, for instance, the following speech by an irate teacher. Though the teacher’s argument does not include signal words, see if

    you can identify which statements are the reasons and which one is the conclusion.

    Philip, I think you really aren’t very interested in passing this course.

    You’ve been late to class five times and absent twice. Moreover, your last

    quiz shows you aren’t studying very hard, either. What have you got to

    say for yourself?

     The teacher stated the conclusion first and then gave the reasons to support it. The conclusion is that Philip is not very interested in passing the course. This conclusion is based on three reasons: (1) Philip has been late five times. (2) He has been absent twice. (3) He has failed his last quiz.

     Signal words can help you even when the words are not used in an argument. If you are having trouble identifying the reasons and conclusion of an argument, restate it to yourself, using signal words; they will show you the relationship between the parts of the argument. For example, you could restate the teacher’s argument this way:

    Because you’ve been late to class five times, have been absent twice, and

    have failed your last quiz, it follows that you really aren’t very interested

    in passing this course.

    Valid Conclusions

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     A conclusion is valid if it follows logically from the reasons the

    evidence given to support it. We can say that the teacher’s conclusion that Philip is not very interested in passing the course is valid; the teacher’s reasons logically support this conclusion. If the teacher had said that Philip was not interested in graduating from school, however, he or she would have been making too general a statement for the evidence given. Perhaps Philip did very well in his other classes.

     Now examine the following argument. Does the conclusion follow logically from the reasons?

     Reason 1: Congressman Hill omitted some of his income from his

     income tax return.

     Reason 2: Governor Moore exaggerated her charitable contributions

     on her income tax last year.

     Conclusion: Most politicians cheat on their income tax.

     This argument is illogical, even though both reasons may be true. Two politicians are not enough evidence for such a sweeping conclusion. The speaker is making a hasty generalization, a general statement based on a small sample of

    cases. It is the same type of mistake in reasoning Philip’s teacher would have made in claiming Philip was not interested in graduating. This type of error in logic is called a fallacy, an error in reasoning.

     In the argument below, three reasons are given, followed by four possible conclusions. Three of the conclusions are hasty generalizations. The fourth is a valid conclusion. Choose the one conclusion you think is valid and put a check mark beside it. Then read the explanation that follows.

    1. The first time I went to that beach, I got a bad case of sunburn.

    2. The second time I went to that beach, I couldn’t go in the water

    because of the pollution.

    3. The third time I went to that beach, I stepped on a starfish and had to

    go to the emergency room to have the spikes removed from my foot.

    Which of the following is a valid conclusion that can be drawn from the

    evidence above?

    a. That beach is unsafe and should be closed.

    b. I’m never going to that beach again.

    c. I should stay away from beaches they’re no good for me.

    d. I’ve had a string of bad experiences at that beach.

     The correct answer is d. Answer a is simply not supported by three

    isolated instances; we’d need many more reports of dangerous conditions

    before considering having the beach closed. Answers b and c also assume

    more than is stated in the evidence; perhaps the speaker is persistent and will

    give the beach another chance. Only answer d if fully supported by the three

    reasons given in the argument.

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    Supporting a Conclusion

     As you have seen, in a valid argument the conclusion must follow logically from the evidence provided to support it. Moreover, the evidence itself should be dependable, sufficient, and relevant.

Dependable Evidence

     Evidence is more dependable when it is based either on someone’s first-

    hand experience or on expert sources. Let’s say that it’s 4 P.M., and you’re getting ready to go to the library to study. The last time you were out, at noon, the sun was shining brightly. Which of the following would convince you that you needed to take an umbrella with you?

     a. The weather forecast in last night’s newspaper that predicted a

     thunderstorm for late this afternoon.

     b. A student who says he looked out the window a few minutes ago

     and thinks that it’s raining outside.

     c. Another student who comes in form outside and reports that it’s just

     started to rain heavily.

    Similarly, which of the following people would be most likely to convince you that certain lizards are able to grow new tails?

     a. Your seven-year-old brother.

     b. A cab driver.

     c. A well-known biologist.

    In each case, the correct answer is c. There’s simply no substitute for the first-

    hand account or the acknowledged expert in a field. Both can be depended on. And the more dependable the evidence is, the more accurate it is likely to be.

Sufficient Evidence

     An argument without sufficient evidence is thin and unconvincing.

    Suppose you are about to register for an English class and meet a friend who is a year ahead of you in school. You tell her you are trying to find a good instructor for English, and the conversation continues as follows:

     “Whatever you do, don’t take Mr. Smith,” says your friend.

     Mr. Smith teaches the section that best fits your schedule, so you ask, “Why not?”

     “Just don’t take him,” your friend answers. “If you do, you’ll be sorry. I certainly was.”

     “Is he unreasonable?” you ask. “Is he dull? Does he give low grades? Too many papers? Not enough papers? What’s wrong with him?”

     “Okay,” your friend replies. “Take him if you insist. Just remember that he was the biggest disappointment of my college career.”

    You might wind up taking Mr. Smith’s class just to find out what he is like. Your friend’s argument may have made you suspect she did not know what she was talking about.

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     Whether in writing or in speaking, a critical thinker will be skeptical about any conclusion that is supported by insufficient reasons. If a writer wishes to argue against capital punishment, he or she will not be very persuasive with just one example or one statistic. After all, that one example or statistic could be an accident. And a poll taken among a thousand people will be more reliable than one taken among only a hundred. In other words, don’t settle for just some

    evidence demand enough evidence.

Relevant Evidence

     Supporting evidence must also be relevant. Just as a conclusion must

    follow logically from the evidence, the evidence presented must lead logically towards the conclusion. A statement may be true but have nothing to do with the issue. Read the following paragraph and try to find the sentence that does not support the conclusion.

    Sigmund Freud was one of the most important scientists of the twentieth

    century. He was among the first to study mental disorders, such as

    hysteria and neurosis, in a systematic way. He developed the theory of the

    unconscious and showed how people’s behavior is greatly affected by

    forgotten childhood events. His discoveries are the basis of

    psychoanalysis, a method of treating mental illness that is still important

    today. He was highly regarded by scientists of his time.

     The conclusion of this argument is that Freud “was one of the most important scientists of the twentieth century.” Any statement that doesn’t help prove this conclusion is irrelevant. The manner in which the scientists of his day viewed Freud isn’t

    as logical reason for his being one of the most important scientists of this century. Many scientists have been highly regarded in heir time without being very important. Thus the last sentence is irrelevant to the argument. In including it, the author was (intentionally or not) changing the subject, another type of error in reasoning.

Some Logical Fallacies

     A fallacy is a flaw in reasoning that leads to an illogical argument. Like propaganda, fallacies often seem reasonable at first, but a closer look reveals how illogical they are. Learning to spot fallacies will help you in evaluating the validity (soundness) of arguments. A conclusion that is reached because of a fallacy may be a good one but it will not be a valid one if it has not been proven by the evidence given.

     The following are explanations of eight common types of fallacies. The first four have to do with ignoring the issue; the second four involve arguments that over generalize or oversimplify issues.

Fallacies That Ignore the Issue

    1. No Support: Circular Reasoning

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     Part of a conclusion cannot reasonably be used as evidence to support it. That type of argument is called circular reasoning, also known as begging the

    question. A simple and obvious example of such reasoning is: “Mr. Green is

    a great teacher because he is so wonderful at teaching.” The reason given in this argument is really the same as the conclusion. We still do not know why he is a great teacher. No real reasons have been given the statement merely

    has repeated itself.

    2. Wrong Support: Personal Attack

     This fallacy often occurs in political debate. Here’s an example:

    Senator Snerd’s opinions on public housing are worthless. He is

    the type of man who is soft on communism, having consistently

    voted against funding our democratic allies in Central America.

    Senator Snerd’s position on Central America may or may not be wrong, but it has nothing to do with the value of his opinions on public housing. This kind of fallacy ignores the issue under discussion and concentrates instead on the character of the opponent.

3. Wrong Support: Straw Man

     An opponent made of straw can be defeated very easily. Sometimes, if one’s real opponent is putting up too good a fight, it can be tempting to build a

    scarecrow and battle it instead. For example, take the following passage from a debate on the death penalty.

    Ms. Collins opposes capital punishment. Letting murderers out on

    the street to kill again is a crazy idea. If we did that, no one would

    be safe.

    Ms. Collins, however, never advocated “letting murderers out on the street to kill again.” In fact, she wants to keep them in jail for life rather than execute them. This fallacy suggests that the opponent favors an obviously unpopular cause when the opponent really doesn’t’ support anything of the kind.

4. Wrong Support: Changing the Subject

     This method of arguing tries to divert the audience’s attention from the true issue by presenting evidence that actually has nothing to do with the argument. You have already encountered this fallacy in the discussion and practice on relevant reasons. Here are other examples:

     I think you should buy a bird, not a dog; many dogs shed all over the

     house. (Saying that many dogs shed is beside the point; it is possible to

     buy a dog that does not shed).

     The congressman is clearly an able leader; he has a warm family life and

     attends church every Sunday. (Mention of the congressman’s family and

     church life sidesteps the issue of just how able he is).

    This fallacy is also called a red herring. In a fox hunt, drawing a red herring

    across the dogs’ path causes them to lose the scent and allows the fox to

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    escape. Someone who changes the subject when arguing may hope the audience will lose track of the real point of the argument.

    FALLACIES THAT OVERGENRALIZE OR OVERSIMPLIFY

5. Hasty Generalization

     To be valid, a conclusion must be based on an adequate amount of evidence. Someone who draws a conclusion on the basis of insufficient evidence is making a hasty generalization. This is a very common fallacy. It

    is not unusual to hear an argument like this one:

     The Chinese people have an inherent talent for art. Two Chinese girls took an art course with me last semester, and they were the best students in the class.

     Forming a conclusion about the quarter of a billion Chinese people in the world based on two examples is an illogical jump.

6. False Cause

     You have probably heard someone say as a joke, “I know it’s going to rain today because I just washed the car.” The idea that someone can make it rain

    by washing the car is funny because the two events obviously have nothing to do with each other. However, with more complicated issues, it is easy to make the mistake known as the fallacy of false cause. The mistake is to

    assume that because Event B follows Event A, Event A has caused Event B.

     Cause-and-effect situations can be difficult to analyze, and people are often tempted to oversimplify them by ignoring other possible causes. Consider this argument:

     The Macklin Company was more prosperous before Ms. Williams became president. Clearly, she is the cause of the decline.

    (Event A: Ms. Williams became president. Event B: The Macklin Company’s earnings declined.)

     What other possible causes could have been responsible for the decline? Perhaps the policies of the previous president are just now affecting the company. Perhaps the market for the company’s product has changed. In

    any case, it’s easy but dangerous to assume that just because A came before B, A caused B.

7. False Comparison

     When the poet Robert Burns wrote, “My love is like a red, red rose,” he meant that both the woman he loved and a rose are beautiful. In other ways

    such as having green leaves and thorns, for example his love did not

    resemble a rose at all. Comparisons are often a good way to clarify a point. But because two things are not alike in all respects, comparisons (sometimes called analogies) often make poor evidence for arguments. In the error in reasoning known as false comparison, a comparison is made in which the

    differences between two things are more important than their similarities. For example, read the following argument.

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     It didn’t hurt your grandfather in the old country to get to work without a

    car, and it won’t hurt you either.

     To judge whether or not this is a false comparison, consider how the two

    situations are alike and how the differ. They are similar in that both involve a

    young person’s need to get to work. But the situations are different in that the

    grandfather didn’t have to be at work an hour after his last class. In fact, he

    didn’t go to school at all. In addition, his family didn’t own a car he could use.

    The differences in this case are more important than the similarities, making it

    a false comparison.

    8. Either-Or Fallacy

     It is often wrong to assume that there are only tow sides to a question.

    Offering only two choices when more actually exist is an Either-Or Fallacy.

    For example, the statement “Either you are with us or against us” assumes that

    there is no middle ground. Or consider the following:

     People opposed to unrestricted free speech are really in favor of

    censorship.

     This argument ignores the fact that a person could believe in free speech

    as well as in laws that prohibit slander or that punish someone for yelling

    “Fire!” in a crowded theater. Some issues have only two sides (Will you pass

    English, or won’t you?), but most have several.

PRACTICE

    A. In each cluster below, three statements are reasons. One is a conclusion. Label

    each as a reason (R) or a conclusion (C).

    1. _____ The record shop was darkened and empty.

     _____ Its door was padlocked.

     _____ Its display window was empty except for a sign reading

     “Bankruptcy Sale Friday.”

     _____ The record shop’s owner had gone bankrupt.

    2. _____ My sister must prefer shopping at home to going to the store.

     _____ She sends away for every catalogue that’s printed.

     _____ She orders items from department store circulars.

     _____ She watches the Home Shopping Network ten hours a day.

    B. Circle the letter of the sentence that states a valid conclusion based on the

     evidence in each group below.

     Group 1

     *A woman was robbed and beaten on her way home from the bus.

     *She did not get a very good look at her attacker, but she said it was a man

     wearing jeans and a sweat shirt.

     *The woman was taken to the hospital to have her injuries treated; she was

     released very quickly.

     Which of the following is a valid conclusion that can be drawn from the evidence

     above?

    a. The woman was careless about where she walked.

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    b. Her attacker will never be found.

    c. Her injuries were not terrible.

    d. She will never take that bus at that time again.

Group 2

     *A dozen children who were at the shore last weekend came down with

     viral infections.

     *A pipe on the waste-disposal system of a nearby city broke, and waste

     was spilled in waters near the shore.

     *The waste-processing system does not totally clean all the city waste. Which of the following is a valid conclusion that can be drawn from the evidence

    above?

    a. The children’s infections had nothing to do with the waste spill.

    b. The children’s infections were certainly the result of the waste spill.

    c. The children’s infections might have resulted from the waste spill.

    d. The city waste workers were careless.

Answers

A.

     1. R, R, R, C

     2. C, R, R, R

    B.

     1. C

     2. C

    Adapted from John Langan’s Ten Steps to Improving College Reading Skills. Revised: 4/20/2012 8

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