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Applied logicApplied logic应用逻辑应用逻辑
主讲人：荣立武主讲人：荣立武单位：山东大学哲学与社会发展学院单位：山东大学哲学与社会发展学院Email: [email protected]: [email protected]
Chapter 2: argumentChapter 2: argument
table of contentstable of contents• 2-1 What is argument
• 2-2 Statements
• 2-3 Premises and conclusions
• 2-4 Do the premises support its conclusion in an argument?
• 2-5 Deductive and Inductive arguments
• 2-6 Restatement: deduction, validity, and soundness
table of contentstable of contents• 2-7 induction, strong arguments, and cogent arguments
• 2-8 the burden of proof
• 2-9 analyzing argument
• 2-10 necessary and sufficient condition
2-1 Reasonable :focus on arguments In fact, you evaluate arguments and assertions everyd
ay: when choosing your breakfast cereal, evaluating reports on the effects of the caffeine in your coffee, reading your morning paper, deciding how to cast your vote.
2-1-1Reasonable :focus on argumentsDefinition-1 [论证 argument]
An argument is a set of statements (or propositions), which is an attempt to prove a demonstration of the truth of a conclusion based on the truth of every premise.
Premises
Conclusion
Argument form
2-1-2 Focus on arguments: Argument skills When you make a conclusion from known
information, and conduct an further action for a certain purpose, you should persuade yourself why I must do like that. Personally, if you be in the face with your friends’ misapprehension, your opponents’ rebuke, how to state the reasons of your behavior for your friends’ support, and how to response your rival’s challenge?
At this moment, you should employ your talents of arguing with them.
2-1-3 Focus on arguments: Improper or incorrect methods of argument Speaking aloud Personal attacking Continuously restate your motivation Rebuke in a hurry even if you don’t understand what
your rival says. If you want to argue efficiently, you should learn to
evaluate an argument.
2-1-4 What constitutes an arguments An argument involves giving reasons that are supposed to
support a certain conclusion. In an argument a set of statement is arranged in such a way that one is supposed to follow from the others.
So, arguments differs from explanations, reports, contracts, ceremonies, questions, instructions, promises, pleas, curses, prayers, poems, exhortations, songs, and sweet talks.
Exercise 2-1Requirement: Determine which of the following are arguments and which
are not. (Don’t worry about whether the arguments are good or bad; just distinguish the arguments from the non-arguments).
Remember: an argument occurs when one or more claims (the premises) are offered as a reason for accepting the other claims (the conclusion).
Then for each of arguments, state the conclusion.
Exercise 2-1 1. The Directory of Intentional Communities lists
more than 200 groups across the country organized around a variety of purposes, including environmentally aware living.
Exercise 2-1 2. Carl would like to help out, but he won’t be in tow
n. We will have to find someone else who owns a truck.
3. In 1976, Washington, D.C., passed an ordinance pr
ohibiting private ownership of firearms. Since then, Washington’s murder rate has shot up[ 急升 ] 121 percent. Bans on firearm are clearly counterproductive [ 适得其反 ].
Exercise 2-1 4. Computers will never be able to converse
intelligently through speech. A simple example proves this. The sentences “How do you recognize speech?” and “How do you wreck a nice beach?” have different meanings, but they sound similar enough that a computer could not distinguish between the two.
Exercise 2-1 5. You guys charged too much for fixing my car. It
only needed new spark plugs, which are fairly inexpensive and are easy to install. So I don’t think I should have to pay this outrageous repair bill.
6. I am not paying that repair bill. I may have to call the state attorney general’s office, maybe my client rating will be ruined, perhaps they will sue me. I don’t care what happens; I’m still not paying.
Exercise 2-1 7. To be successful in your logic course, it is
important to do as many exercises as possible. It would also help a lot to read the chapters in the text, perhaps even a couple of times. And attending class regularly wouldn’t hurt.
Exercise 2-1 8. If the moon is made of green cheese, then there are
mice on the moon. The moon is made of green cheese. Therefore, there are mice on the moon.
9. I solemnly swear to tell the truth, the whole truth, and nothing but the truth.
Exercise 2-1 Three reliable witnesses saw the defendant in New
York just one hour before the murder took place in Los Angeles. There is no way the defendant could be guilty of the murder. Besides, the defendant had no reason to kill the guy-they were good friends.
2-2 Statements an argument-premise and conclusion-is constituted by
statements. statements (or propositions) A statement is a claim that is true or false; that is, a
statement has a truth value. Statement and sentence-not all sentences are statements: Please close the door.-the same statement can be expressed by different
sentence. The defendant struck Ralph. The defendant hit Ralph.Ralph was struck by the defendant.
Exercise 2-2 For the following, tell which are statements and
which are not statements.
1. if you don’t close the door, the dog will get out.
2.Don’t rush! Think through each question before answering.
3.Either there will be a reduction in air pollution or we will suffer severe global warming.
Exercise 2-24.Our sun is one of the smallest stars in this galaxy.
5.All penguins cheat at poker.
6.Bruce lied when he said this exam would be easy.
7. I confess, whatever I said ia a lie.
2-3 Premises and conclusions
Argument are made of premises and conclusions. The conclusion is what the argument is trying to prove.
The premises are the reasons given for the conclusion, the statements made in support of the conclusion.
How to identify the premise and the conclusion in a argument?
Indicative words: Premises: since, due to the fact that, because. Conclusions: therefore, hence, it follows that,
consequently.
2-3-1 Premises and conclusions
The structure of an argument : “We should bet on (racehorse) General Assembly. After all, General Assembly runs very well on muddy tracks. And since it rained all morning, the track must be muddy ”
Ultimate conclusion: We should bet on (racehorse) General Assembly
Premise:
(1)General Assembly runs very well on muddy tracks
(2) the track must be muddy
subargument : conclusion-- the track must be muddy.
premise------ it rained all morning
2-3-2 To think over the question, and then seek to the answer
The vital first step in critical thinking is to determine the exact conclusion.
Sometimes, when participants in an argument establish exactly what they are arguing about, they often find that they have been arguing at cross-purposes.
When considering an argument, the essential question is: what is that supposed to prove? An effective argument in support of one conclusion may be a total washout in support of some other conclusion.
2-3-3 To think over the question, and then seek to the answer
For example: (1) an argument describing the number of farmers,
manufacturing workers, and warehouse workers who depend heavily on tobacco for livelihood may be very effective in establishing that tobacco provides jobs for many people; however, the same argument will be useless in proving that tobacco is not a health hazard.
2-3-4 To think over the question, and then seek to the answer If you serve on a jury, you should make clear what’s
the question, because the conclusions being aimed at by the prosecuting and defense attorneys are frequently quite complicate.
What exactly is the goal of the defendant’s attorney? What is he or she attempting to prove to you? How would you state that conclusion?
2-3-5 To think over the question, and then seek to the answer
The goal of the defendant’s attorney (1) to prove that the defendant is innocent. (2) to prove that the defendant is not guilt. (3) to prove that the defendant has not been proved guilty.
-the defense attorney might fail to prove that the defendant is innocent of the crime, but if he succeed in establishing that the defendant’s guilt has not been proved, then it is enough to make the jury send a favorable conclusion to the defendant.
2-3-6 To think over the question, and then seek to the answer For example: The defense can show that the prosecution’s key
eyewitness is unreliable, that may knock an unbridgeable gap in the prosecution’s attempt to prove guilt.
So, if you would be in a jury, you should make clear that the key question is whether the defendant has been proved guilty or not.
2-3-7 Advertisements for Total cereal
Premises: Total contains 100% of recommended daily
allowance of nine vitamins and iron, and raisin bran contains only 25%.
Conclusion: Total is more nutritious than raisin bran. Is it a sound argument?
2-3-8 Advertisements for Total cereal
Reconstruct the argument: Premises: (1)Total contains 100% of recommended daily allowance of
nine vitamins and iron, and raisin bran contains only 25%. (2) A cereal that contains more vitamins is more nutritious
than a cereal containing fewer vitamins. Conclusion: Total is more nutritious than raisin bran.
2-3-9 Implications from that case (1)Don’t be missed by deceiving advertisement. (2) Whenever you are evaluating an argument-
whether in a jury or watching television or reading an editorial- first pike out the conclusion of the argument and then decide how well the argument supports the conclusion.
2-3-10 Implications from that case
(3) recognizing the conclusion is always essential to evaluating an argument, for arguments are not strong or weak in absolute terms: an argument is strong only if it strongly supports its specific conclusion. A very impressive argument may give strong grounds for one conclusion and be totally useless and irrelevant for establishing some other conclusion.
Exercise 2-3(finding the conclusion) What is the exact conclusion of each of the following
argument? (The conclusion may not be stated precisely; in fact , in some of the arguments it may not stated at all, but only implied.) It is important that you state it very carefully, perhaps more carefully than it is stated in the original argument. There is not a single exact way the conclusion must be stated; different people may phrase the conclusion differently. It is, however, important to specify the key assertion being made in the conclusion. That is, exactly what does the arguer want to convince you of?
Exercise 2-3(finding the conclusion)1. When we consider how splendidly the planets are
arranged in their orbits, how the Earth is positioned at the right distance from the Sun, how the eye is designed to see and the hand is fashioned for grasping, then we must conclude that it was all arranged by some higher, greater intelligence.
Exercise 2-3(finding the conclusion)2. Small farms are probably not the most efficient way
to produce agricultural products; but efficiency is not everything. We must also consider the heartbreak of those who lose farms that families have operated for generations, the satisfaction people receive from owning and operating their own farms, the independent lifestyles of those who run their own farms and their own lives. Efficient or not, we must find some way to sustain and support the proud tradition of small farms in the United States.
Exercise 2-3(finding the conclusion)3.Capital punishment requires that a number of people parti
cipate in deliberately putting a healthy human being to death. Participating in such a process-dragging a condemned( 宣判死刑 ) human to an execution chamber, strapping that person into an immobile position, administering the killing jolt or the lethal potion( 毒剂 ), officially witnessing the whole ghastly process-must inevitably have the effect of brutalizing( 伤害 ) those who participate, making them more callous( 冷酷 ) and blunting their human sympathies. Even if capital punishment could be justify on other grounds, that is high a price to pay.
Exercise 2-3(finding the conclusion)4. Look, I don’t who robbed the First Federal Bank last
September. And the district attorney doesn’t know, and my client (the defendant in the bank robbery case) doesn’t know, and you, the conscientious and careful members of the jury, don’t know who robbed the bank. It would be nice to get the question cleared up. I sincerely wish I could tell you who did rob the First Federal, and we could send the robber to jail, where the robbers belong. But we don’t know who committed the crime: sometimes we must live with the fact that we do not know the answers to important questions.
Exercise 2-3(finding the conclusion) (continuing) But there is one important thing that you
and I and the judge and indeed all good citizens of these United States do knows: Every person has the right to be presumed innocent unless he or she is proved guilty beyond a reasonable doubt. And it is that certainty , a certainty that is the bedrock of our justice system, that I know each of you jurors will keep in mind as you consider your verdict.
Exercise 2-3(finding the conclusion)
5. We shall never get anywhere debating the moral right or wrong of abortion( 堕胎 ). The issue is too embroiled( 被卷入 ) in conflicting religious beliefs and social traditions. And besides, there is no agreement about the best way to pursue answers to moral question: there is no agreed-upon “ethical method” comparable to scientific method. So we should leave the question of abortion to each person’s individual conscience or faith, because certainly it would be foolish to attempt to enforce a law on an issue on which there is no moral agreement in society. For when we try to force laws upon people when there is no underlying moral consensus in support of those laws, we simply encourage lawlessness and disrespect for the law.
Exercise 2-3(finding the conclusion)
6. Millions of pounds of public money are spent defending riverside farmland from flooding. Some of this money should be given to farmers to compensate them for taking such land out of production. This would save money and would benefit the environment, since if rivers were allowed to flood, their natural flood plains would provide wetland meadows and woodland rich in wildlife.
Exercise 2-3(finding the conclusion)
7. We could reduce road accidents by lowering speed limits, and making greater efforts to ensure that such limits are enforced. But, because this would inconvenience the majority who drive safely, this would be an unacceptable solution to the problem of careless drivers who are unsafe at current speed limits.
Exercise 2-3(finding the conclusion)
8. Television advertising agencies are very clever in the way that they construct ads. Often the ads are similar to the cartoons that the children enjoy. Children see these characters interacting with a certain product and associate their affection for the character with affection for the product. The companies do not want the children to perceive a difference between the shows they are watching and the advertisements. By using this strategy, these companies take advantage of the fact that children are often not able to discriminate between the cartoons and the ads and do not understand that these things offered come at a cost. Often the advertising is about sugary snacks or fatty foods, leading the children down a path to bad health. Advertising geared towards children should be regulated -just as there are regulations now about tobacco and alcohol ads targeted at children.
Exercise 2-3(finding the conclusion)
9. Cell phones are becoming a large part of today's society bringing with than benefits and drawbacks. They are beneficial for those with tight schedules and in case of emergencies. Cell phones can also come in handy for parents to check up on their children. Even though cell phones do carry benefits, the drawbacks are in their inappropriate use. When a cell phone rings or owners talk on them during a lecture or a concert, a major disruption in the concentration of others is inevitable. Even though there are suggestions in polite society to leave them off, perhaps we need stronger penalties associated with abuse of the growing population of cell phones.
2-3 Premises and conclusions Premises and conclusions are statements. They make
claims, and they are either true or false. But while the premises and conclusions of arguments are true or false, arguments are not true or false. Instead, arguments are valid or invalid, sound or insound, strong or weak, cogent or uncogent.
2-3-1 Premises and conclusions Evaluation of an argument comprises two distinct and
essential consideration. First, do the premises support the conclusion? Second, are the premises actually true? Clearly, we are easy to judge the second point.
For example:
All dogs have eight legs.
The President is a dog.
Therefore, the President has eight legs.
2-4 Do the premises support the conclusion?
Difinition-2 [有效性 Validity] An argument is valid iff it is impossible for the premises of
the argument to be true whilst the conclusion is false.Definition-3 [逻辑 logic] 逻辑是研究区别有效论证与无效论证方法和原则的科
学。 Logic is the study of the methods and principles used to dis
tinguish valid argument from invalid argument.
2-4-1 Do the premises support the conclusion? But, what is a valid argument? In other words, what is the
conclusion really “following from” the premise?
After all, an argument with all true premises may fail to support its conclusion, while an argument with false premises may strongly supports its conclusion.
What is the meaning of saying that premises of an argument support its conclusion?
1% of ancient Greek are philosophies.
Aristotle is one of ancient Greek.
So, Aristotle is one of philosophies.
2-4-2 Do the premises completely support the conclusion? The validity of an argument: it is impossible for the
premises of the argument to be true whilst the conclusion is false.
For example:
1% of ancient Greek are philosophies.
Aristotle is one of ancient Greek.
So, Aristotle is one of philosophies.
The conclusion could be false, even if the premise is true.
2-4-3 Do the premises support the conclusion?
So, if we make clear the concept of “possible” or “impossible”, then we grasp the key points for understanding “validity” of an argument.
-possible and impossible: Whether a statement is actually true or false, if it can be
conceived to be true, then we say that it is true is possible. For example, “I am an American” is true is possible.So, we say that a statement is true is impossible, we mean it
can’t be conceived to be true under any situation.For example, “There is a spear which can penetrate any
shield and a shield which can’t be penetrated by any spear ” is impossible.
2-4-4 Do the premises support the conclusion?
So, if all of the premises of an argument are supposed to be true (even if it can be false in fact), its conclusion can’t be false (that it is false is impossible), we say that the argument is valid, otherwise it is invalid.
Question: what is the meaning of saying that an argument is invalid?
At this time, the premises offer the strongest support to its conclusion.
Question: what is the meaning of saying that an argument is not one of the strongest argument?
2-4-5 Do the premises support the conclusion?
Furthermore, if the premises are all true for a valid argument, then we say that argument is sound, otherwise it is unsound.
Question: what is the meaning of saying that an argument is unsound?
2-4-6 Do the premises support the conclusion?
Please judge the following examples are valid or invalid, sound or unsound?
(1)1% of ancient Greek are philosophies.
(2) Aristotle is one of ancient Greek.
(3) So, Aristotle is one of philosophies.
(1) All dogs have eight legs.
(2) The President is a dog.
(3) Therefore, the President has eight legs.
2-4-7 Do the premises support the conclusion?(1)All of human beings are animals.
(2) Aristotle is one of human beings.
(3) So, Aristotle is one of animals.
2-5 Deductive and Inductive arguments
What are the differences between a deductive and an inductive argument? There are several, but they all stem from this key difference: inductive arguments go beyond the information contained in the premises; inductive arguments make a projection based on given information. Deductive arguments draw out the implications of the premises; they draw conclusions that are already contained in the premises.
2-5-1 Deductive and Inductive arguments Inductive arguments: (1)The sun rose in the east sky yesterday. (2) The sun rose in the east sky the day before
yesterday. (3) The sun rose in the east sky every day in my life. (4)So, the sun will rise in the east sky tomorrow. (or
the sun always rises in the east sky. )
2-5-2 Deductive and Inductive arguments Inductive arguments: (1)Zhanshan is one of my classmates, and she is dilig
ent. (2) Lisi is one of my classmates too, and he is diligent. (3) Wangwu is one of my classmates either, and he is
diligent. (4)So, all of my classmates are diligent.
2-5-3 Deductive and Inductive arguments Inductive arguments: (1) If you heat up a piece of copper, it will expand. (2) If you heat up a piece of iron, it will expand. (3) If you heat up a piece of gold, it will expand. (4) A piece of copper, iron and gold are metal. (5)So, if you heat up any piece of metal, it will expand.
2-5-4 Deductive and Inductive arguments deductive arguments: (1) If you disobey intentionally the law of nation you
resided in, you will be punished in the light of the laws of that nation.
(2) Zhanshan beat up a troublesome guy in a bus when he study abroad in Canada, and broke the laws of Canada.
(3) So, Zhanshan will be punished in accordance with related laws of Canada.
2-5-5 Deductive and Inductive arguments The moral (rule) of determining an argument is a
deductive one or inductive one is: you must first determine what the conclusion is, but don’t stop there. Examine the relation between premises and conclusion (is the conclusion implied by the premises or made a projection from the information given by premises); only then can you make a proper decision.
Exercise For each of following cases, first tell whether it is or is
not an argument; second, for each argument determine whether it is deductive or inductive; third, for each of the arguments state the conclusion.
1. All licensed physicians in United States are medical school graduate. Ralph is not a medical school graduate, so Ralph is not a licensed physicians in United State.
2. If you want to live a long and health life, then you should eat lots of fruits and vegetables, and stay away from junk food and fast food. Also, be sure to get some exercise, and try to get a decent amount of sleep. And of course, don’t smoke.
Exercise 3. Susan is a licensed physician, and she is a medical
school graduate. Sarah is a licensed physician, and she is a medical school graduate. Sam is a licensed physician, and he is a medical school graduate. Bradley is a licensed physician, and he is a medical school graduate. Susan is a licensed physician, and she is a medical school graduate. And Teresa is a licensed physician, and she is a medical school graduate. Ralph is also a licensed physician, so he is a medical school graduate.
Exercise 4. We have interviewed 1200 college students, and 900
of them favored 18 as the legal age for purchase of beer. 5. We have interviewed 1200 college students, and 900
of them favored 18 as the legal age for purchase of beer. Therefore, a substantial majority of all U.S. college students favor 18 as the legal age for purchase of beer.
6. we should set 18 as the legal age for purchase of beer. If people are old enough to vote, then they are certainly old enough to drink, and 18-years-olds are indeed old enough to vote.
Exercise 7.The team with the best pitching always wins the World
Series. The St. Louis Cardinals must have the best pitching, because the Cardinals won the World Series.
8. I think Jones—the key witness for the prosecution– probably robbed the bank himself, and is now trying to pin the crime on Smith. In any case, there is certainly a reasonable doubt that Smith (the defendant) robbed the bank, so we should all vote not guilty.
Exercise 9.Either the Chicago Cubs or new York Mets will win
the World Series. The New York Mets obviously will not win the Series, since they have had lots injuries, and their pitching and fielding have both been weak. So Chicago Cubs will win the World Series.
10. Last quarter there were 18 students in the Logic course who never missed a class, and they all passed the course. The quarter before that, 16 students attended every class, and all of them passed also. So if you attend every class this quarter, you will pass the course.
2-5-6 Discussion: Relevant and irrelevant reasons to a specific conclusion Imagine a prosecuting attorney who-in his or her final
argument to the jury-argues quite convincingly that crime is doing terrible damage to our fair city, that criminals must be put behind bars for the protection of society, and that it is the duty of all good citizens to oppose crime.
Those are impressive points. But since the issue is whether the defendant committed the crime, those impressive premises are useless (irrelevant) in establishing that conclusion (that is, the defendant is guilty of the crime).
2-6-1Relevant and irrelevant reasons
Premises (reasons): The US demand for electrical energy will steadily increase over the next three decades.
Is that claim relevant, or irrelevant, to a debate about nuclear energy?
Case 1: if the conclusion is about the safety of nuclear energy, then statements above mentioned is irrelevant.
Case 2: if the conclusion is about the development of nuclear energy contributing to incoming shortage of energy in America, then they are relevant.
2-6-2 Relevant and irrelevant reasons In a debate over whether to build more nuclear power
plants, it will certainly be important to know that whether more power is needed: if no new power sources are required, then that will count against building power plants of any type, including nuclear.
But you might still conclude that we should not build more nuclear power plants- perhaps they are simply too dangerous-even if you recognized that the increase demand for power is a relevant consideration.
If the issue is whether nuclear power plants pose a serious threat to life and health, considerations of need for electrical power are irrelevant.
2-6-3 How to determine the relevance or irrelevance between the premises and the conclusion.
The key point to remember when considering the relevance or irrelevance of premises is this: Premises, reasons, and facts are not in themselves relevant or irrelevant; rather, a premises fact, or reason is relevant or irrelevant relative to a specific conclusion.
When examining an argument, first determine the precise conclusion. Then when considering the premises of the argument-- the reasons given in support of the conclusion--ask:
2-6-4 How to determine the relevance or irrelevance between the premises and the conclusion.
Would the truth of this premise make the conclusion more likely? Would the falsity of this premise make the conclusion less likely? If the answer to those questions are yes, then the premise is relevant and actually contributes something to the argument; if the answer is no, then the premise is irrelevant—throw it away, for it can only confuse the issue.
2-6-5 Case analysis: Reid’s accused of a felony to knowingly possess a firearm The Wisconsin law states that a person is guilty of
that crime if he or she (1) has been convicted of a felony;(2) possesses a gun;(3) knows that he or she possesses a gun.
Reid’s case was unfortunate. Reid had been convicted of a felony many years earlier. After his release from prison, he had lived a number of years without getting into any trouble. He was a man of low intelligence, a functional illiterate, apparently harmless.
2-6-6 Case analysis: Reid’s accused of a felony to knowingly possess a firearm (continuing) He had seen an advertisement for a “training
program” for private investigators. Reid mailed in a few dollars and received a “private detective’s badge,” which he always carried. Reid desperately wanted to find work that would allow him to help people.
In pursuing this detective fantasy, Reid bought a pistol. While in a Milwaukee courtroom (he was unemployed, and he often passed his days around the courts), he showed a sheriff’s deputy the receipt for the pistol he had bought. When the deputy asked Reid to bring in the pistol, Reid immediately did so. And he was arrested. When the case went to the jury, they debated long and hard about their verdict.
2-6-7 Case analysis: Reid’s accused of a felony to knowingly possess a firearm (continuing) Many jurors argued that Reid was
harmless, hardly able to understand the charges against him, certainly not aware that he was breaking the law by purchasing a hand gun and with no intention of breaking the law, carried away by the hopeless fantasy of becoming an important and respected private detective who would fight for those who needed help, a man whose goal was to help others and gain respect for himself rather than to commit a crime or cause harm.
Other members of the jury saw it differently: Reid’s misfortunes are sad but it is irrelevant to final verdict, because Reid is guilty according to the law is written.
2-6-8 Case analysis: Reid’s accused of a felony to knowingly possess a firearm Question:
(1) Did Reid break the law of the felony?
(2) Is it really fair to convict him?
(3) What’s the function of the judge?
Exercise 2-5(Relevant and irrelevant reasons)1. The Alaskan oil pipeline is certainly not a threat to the environ
ment of Alaskan tundra( 冻土地带 )(through which the pipeline passes) or to the Alaskan coastal waters. For after all, it is essential to the economic well-being of the United States that Alaskan crude oil be shipped out of Alaska through an efficient pipeline. Alaska contains the largest oil reserves in the United States, and we must have access to those oil reserves if we are to avoid costly and risky dependence on foreign oil supplies. And the Alaskan pipeline is the most cost-efficient method of making Alaskan oil available to the rest of the United States.
Exercise 2-5(Relevant and irrelevant reasons)2. There is now before Congress a proposed amendment
to the U.S. Constitution that would make it illegal to burn the American flag as an act of protest. Some people oppose this amendment on the grounds that it would, for the first time in U.S. history, place a restriction on the right of political protest, and place a restriction on the right of political free speech. But that’s just false. The proposed ban on flag-burning would in no way restrict free speech. For, after all, the American flag is a great and glorious symbol of our country, and our soldiers have fought and bled and died for that flag for over 200 years.
Exercise 2-5(Relevant and irrelevant reasons)2. (continuing) When it is burned in protest, it cause gre
at pain and anguish to those who dearly love the stars and stripes. Besides, there are lots of ways one can protest without burning the flag: by giving speeches, participating in marches, signing petitions( 请愿 ) ， writing letters; so there would still be plenty of opportunities for political free speech if flag burning were prohibited. So a ban on flag burning obviously would not be a restriction on free speech.
Exercise 2-5(Relevant and irrelevant reasons)3. In the following letter, what is the conclusion of the
argument offered by Benny? What reasons does he give in support of that argument? Is the reply made by Ann Landers relevant to Benny’s argument and conclusion?
Dear Ann Landers; I’m a high school senior who is speaking for a lot
of others my age (17 going on 18). We have a big complaint. First I want to make it clear that we don’t go out and get smashed every night. Most of us are responsible people. The kids who make trouble get the publicity. Good behavior is not news.
Exercise 2-5(Relevant and irrelevant reasons)(continuing) What we are mad about is the attempt to raise the legal
drinking age all over the country from 18 to 21. If we are ole enough to go to war, we should be old enough to drink. I’ll be interesting in whether you duck this issue or print my letter. (Just Benny)
Dear Benny; The folks who want to raise the legal drinking age from 18 to 21
are not being mean. They are trying to save lives-and, I might add, they are succeeding.
Every state, without exception, that has raised the drinking age from 18 to 21 has reported a decrease in alcohol-related teenage deaths and injuries on the streets and highways. I know of few laws that are such surefire( 能达成目的 ) lifesavers.
2-7 Restatement: deduction, validity, and soundness
Note: forms of an valid argument.
Rule 1 [分离规则，Modus Ponens(MP)]
If p, then q,
p,
therefore, q
Rule 2 [三段论规则 ]
All T are J.
M is a T.
Then, M is a J.
2-7-1 Restatement: deduction, validity, and soundness
In analyzing deductive arguments, we applied two standards. Deductive arguments are valid or invalid, and they are sound or unsound. A deductive argument is valid if the truth of it premises guarantees the truth of its conclusion; that is, if its premises are actually true, then the conclusion must be true. If a deductive argument is valid, and all its premises are actually true, then the argument is sound.
2-7-2 Restatement: deduction, validity, and soundness Validity is concerned with the relation between
premises and conclusion, leaving aside the question of whether the premises are actually true; soundness brings in the question of the actual truth of the premises.
2-7-3 induction, strong arguments, and cogent arguments
(1) Inductive argument in our life. (2) Unfortunate turkey or unfortunate human beings (how
to improve the credibility of our inductive argument ?) It is useful to have corresponding standards for
evaluating inductive arguments. But obviously we can’t just use the terms we applied to deductive arguments, because they won’t fit. In a valid deductive argument, if the premises are true, the conclusion must be true.
2-7-4 induction, strong arguments, and cogent arguments
But because inductive arguments make claims that go beyond their premises, they can’t be valid or sound, the way deductive arguments are.
Excellent inductive arguments that contain all true premises still leave the possibility--however slight--that their conclusion are false. So instead of validity and soundness, we will need new terms for inductive arguments, that is, a strong or weak inductive argument and a cogent or uncogent inductive argument.
2-7-5 induction, strong arguments, and cogent arguments When we say that an inductive argument is strong, we
saying nothing at all about the truth of its premises. Rather, we are saying that if its premises are true (not that they are true), then the premises provide strong support for the truth of the conclusion.
2-7-6 induction, strong arguments, and cogent arguments A deductive argument can be valid but unsound (if on
e of the premises of a valid deductive argument is false). Something similar applies to an inductive arguments.
So, just as a deductive argument can be valid but unsound, an inductive argument can be strong but uncogent.
2-7-7 induction, strong arguments, and cogent arguments For a deductive argument to be sound, it must meet two condit
ions: it must be valid, and all its premises must actually true. Along similar lines, for an inductive argument to be cogent, it must be strong, and its premises must actually be true.
If a deductive argument is not valid, or has a false premises (or both), then we say it is unsound. If an inductive argument is either weak or has a false premise (or both), then we say it is uncogent.
2-7-8 induction, strong arguments, and cogent arguments One last point. When we are dealing with deductive arguments,
they are either valid or invalid. There is no in-between. But inductive arguments are different. For example, the united
states has had a flu outbreak every year for the last 5 years, so we’ll probably have one this year. Is that a strong inductive argument? Well, it’s not at all that strong. Certainly, it would be strong, if the premise stated that the united states has had a flu outbreak every year for the last 100 years; it would be weaker, if it cited only the past 2 years.
Exactly when does it pass from weak to strong? There is no bright line. That doesn’t mean that we can never distinguish between strong and weak inductive argument, but it does make things a bit tricky.
Exercise 2-6 Making a choice from ABCD (NOTICE: there is only
one proper answer for each question) 1 ( ) is not a statement.A. If you don’t close the door, the dog will get out. B. Jupiter is not the largest planet in our solar system.C. There is a spear which can penetrate any shield and a
shield which can’t be penetrated by any spear.D. Don’t look at anyone else’s paper.
2. In each argument, there can be only one ( )A. premise B. conclusion C. assumption D. statement
Exercise 2-6 Making a choice from ABCD (NOTICE: there is only
one proper answer for each question)
3. Probably the best advice for anyone trying to identify arguments is to look for the premises firstly.( )
A. True B. False
4. “if I am not ill, then I will arrive at the classroom on time” is a : ( )
A. the premise B. the conclusion C. an argument D. an statement
Exercise 2-6 Making a choice from ABCD (NOTICE: there is only one proper
answer for each question)
5. The word critical in critical thinking refers to: ( )
A. A faultfinding attitude
B. Attempts to win an argument
C. Using careful judgment or judicious evaluation
D. A lack of respect for other people
6. A belief is worth accepting if: ( )
A. We have good reasons to accept it
B. It is consistent with our needs
C. It has not been proven wrong
D. It is accepted by our peers
Exercise 2-6 Making a choice from ABCD (NOTICE: there is only
one proper answer for each question) 7. In a valid deductive argument, if all the premises are true
then the conclusion: ( )A. is probably true B. must be trueC. may or may not be true. 8. If an argument has a false conclusion but all its premises
are true, then the argument cannot be ( ) argument. A. a valid deductive argument B. a cogent inductive argumentC. either valid or cogent
Exercise 2-6 Making a choice from ABCD (NOTICE: there is only
one proper answer for each question)
9. If all the premises of a deductive argument are false, then that argument is : ( )
A. valid B. invalid
C. impossible to tell from the information given.
10. All licensed physicians in the United States are medical school graduates. Ralph is not a medical school graduate, so Ralph is not a licensed physicians in the United States. This argument is a ( )
A. inductive B. deductive
Exercise 2-7 deductive argument or inductive argument Please determine which one is an argument, and then
identify it is an deductive one or inductive one
1.In the last five World Series, the team that is at home for the first game has won the series. Therefore, the Toronto Blue Jays are a good bet to win this World Series, since they are the home team for the first game.
2. If the defendant has a good alibi, then there is reasonable doubt of her guilt. And if there is reasonable doubt of her guilt, then we should find her not guilty. So we should find the defendant not guilty, since she certainly has a very good alibi.
Exercise 2-7 deductive argument or inductive argument Please determine which argument is deductive or inductive
3. All philosophers are rich and good-looking. Bruce is neither rich nor good-looking. Therefore, Bruce is not a philosopher
4. All penguins are great mathematicians. George Bush is a penguin. Therefore, George Bush is a great mathematician.
2-8 the burden of proof Is there a an ocean-bottom ETcity?
You can’t prove it is false that there is no ETcity in the bottom of Pacific Ocean.
So, it is true that there is an ocean-bottom ET city.
Is the argument above mentioned believable? Generally speaking, in each case, if one claims a special,
not well-known statements, and his rival insist on accepted beliefs, then who makes a special one bears the burden of proof.
2-8-1Analysis: There was no real proof for the claim (undersea city
exists), because anyone making a claim bears the burden of proof.
The person making the claim must prove his or her claim true; it is not up to others to prove it false.
The fallacy of appeal to ignorance is committed when someone argues that because his or her claim cannot be proved false, it therefore should be accepted as true.
2-8-2 Why the burn of proof is so important on evaluating an argument?
The “preliminary” question of who bears the burden of proof often has great influence on which side prevails in an argument.
Sex discrimination: who should answer for proving whether there are unfair regulations to pregnant teachers or not?
Placing the burden of proof. Suppose that I am a school district governor, and I impose a
regulation requiring that teachers beyond the fourth month of pregnancy must take an unpaid leave of absence from their teaching jobs. You claim that this rule is unfair to women teachers, because it unreasonably deprives them of the opportunity to work. Does such a regulation treat women unfairly?
2-8-3 Why the burn of proof is so important on evaluating an argument?
(continuing) Before you answer that, think about the prior question: who bear the burden of proof?
You are claiming that my rule unfairly discriminates against women; it is up to you to prove that the rule places a special hardship on women?
Or should the burden of proof be on me? After all, I propose the rule; should it be my burden to prove that the rule does not unfairly discriminate?
2-8-4 The burden of proof in the courtroom Who bears the burden of proof? (who claim, who prove) In fact, when we apply the principle (who claim, who
prove) to the law-suit, then we have the slogan “innocent until proven guilty”.
But why the principle or the slogan hold the prominent position in the system of British and American law ?
2-8-5 The burden of proof in the courtroom
(1) the principle is the simply the correct manner of reasoning.
(2) the discussion about the burden of proof can make anyone’s extraordinary claim impossible, because he should prove what he claims. So no one can get a credible conclusion by taking “appeal to ignorance”.
2-8-5 The burden of proof in the courtroom
(3) there is another reason for favoring a strong presumption of innocence. It has less to do with logic and more with our principles of individual freedom and justice.
We believe that the rights and freedom of the individual are fundamental, and we oppose sacrificing individual rights.
Therefore, the general presumption must be that the individual’s rights and freedom should not be interfered with. Any denial of individual liberty requires powerful overriding reasons and strongest and conclusive proof.
Exercise 2-8 the burden of proof Each of the following cases requires you to decide where the
burden of proof belongs. In each case, you must decide who is making a claim, which side is asserting something special, and who is entitled to claim that are relying on accepted beliefs and are not asserting anything that requires special proof.
1. I am proposing to place a new mouthwash on the market. The Food and Drug Administration requires that I provide extensive tests demonstrating the safety of the mouthwash. But it is unfair to me, if anyone has any doubts about the safety of my production, then the doubter should be required to offer proof that my production is dangerous. I have not made any claims about the safety of my production, so why should I be asked for any proof?
Exercise 2-8 the burden of proof 2. Suppose that an industry wishes to place a landfill on
some property near a river. Some environmentalists claim that the landfill is a hazard to the river, since landfills frequently leak and the leakage from this one would be likely to enter into the nearby river. The industry claim that it will not pollute the river, that there is no danger to the environment from the landfill, and that environmentalists are extremists who are worry about nothing.
Exercise 2-8 the burden of proof 3. When, in sixteenth century, Copernicus proposed the t
heory of solar system, it contradicts common sense. It seems obvious that the Earth is stationary, and obviously false that the Earth is traveling at a high rate of speed in orbit around the Sun. People felt that unless Copernicus could supply strong proof of the Copernican system, then the geocentric( 地心说 ) view should be upheld. Did they place the burden proof in the right place?
Exercise 2-8 the burden of proof 4. Prior to the U.S. attack to Iraq, the U.S. asserted that Ir
aq had weapons of mass destruction (in violation of United Nations). The U.S. and the weapons inspectors in Iraq could offer no proof of such weapons, but the Bush administration insisted that the U.S. was not obligated to provide such proof. At a Pentagon( 五角大楼 ) briefing ， Defense Secretary asserted that: “the President has repeatedly made clear that the burden of proof is not on the United Nations or the international community to prove that Iraq has these weapons. The burden of proof is on the Iraqi regime to prove that it is disarming and to show the inspectors where the weapons are.”
2-9 analyzing argument When analyzing an argument, start with the conclusio
n. If you are trying to a compelling argument, first decide exactly what conclusion you want to establish.
If you are evaluating someone else’s argument, first determine exactly what the argument is supposed to prove.
When you have picked out the conclusion, then you can examine the structure of the argument in support of the conclusion.
2-9-1 do we need more nuclear plants
We should not build more nuclear power plants in the U.S. Nuclear power is a dangerous technology: we have already experienced several nuclear accidents, and nuclear accidents have the potential to be catastrophic; even if the operators are well trained and careful and made no errors and all safety features are incorporated into the design—which is unlikely—there is always the danger that a nuclear power plant might be the target of a terrorist strike, with terrible consequences for public safety. Furthermore, nuclear power place an unfair burden on future generations: while we gain the benefits of the electricity produced, we leave for the future generations the legacy of dangerously radioactive spent nuclear fuel.
2-9-2 do we need more nuclear plants
(continuing) It is selfish and unfair to use a technology that benefits the present at the expense of future generations. Finally, we do not really need the increase power that more nuclear power plants would generate. Through careful conservation of energy—including strict requirements for energy efficient appliances and equipment and automobiles and houses—we could reduce our power needs, and through greater use of solar and hydroelectric and wind power, we would substantially increase our supply of energy. So we should put an immediate stop to the building of new nuclear power plants.
2-9-3 Argument structure Convergent argument In an argument, if there are independent reasons, each
offering independent support for the conclusion of this argument on which they all converge from separate directions, then this argument structure is often called a convergent argument type.
In a convergent argument, the different reasons are independent of one another, and when one falls it does not take the others down with it.
No additional nuclear power plants should be built
Nuclear power plants
are dangerous
Use of nuclearpower is unfair
to futuregenerations
The power from additional nuclear
power plants isnot essential.
Level-1
2-9-4 Linked argument In some arguments, the premises, that is the reasons
given in support of the conclusion, are linked together like a chain, and if one link breaks, the entire argument fails.
The linked argument is thus only as strong as its weakest link.
In short, a linked argument is an argument in which the reasons given depend on one another for their strength. Separately, each premise offers little or no support for the conclusion; together, they may form a powerful argument.
White Jaguar automobiles are quite unusual in this area. The defendant owns white jaguar, and the car from which the fatal shots were fired has been identified by several witness as a white Jaguar. Therefore, there is some reason to think that the defendant is guilty of the drive-by murder.
Defendant is guilty
Defendant owns A white Jaguar
White Jaguarsare rare
Fatal shotsfired from
White Jaguar
Level-2-1
Nuclear power plants are dangerous
There have been severalnuclear accidents
There is danger of aterrorist attack on a nuclear power plant
Level-2-2
Use of nuclear power is unfair to future generations
Use of nuclear power leaves
long-termradioactive wastes
Continued monitoringand isolation of
dangerous nuclearwaste will be burdensome to
future generations
It is unfair to providepresent benefits at the expense of
future generations
Level-2-3
The power from additional nuclear power plantsis not essential
Energy conservation could reduce power
need
Solar and hydroelectricand wind power could
increase our energysupply
Exercise 2-9 For the following argument, state the conclusion and the
premises; then show whether that structure is convergent or linked, and give reasons for your answer.
1. Transplanting animal organs into humans should not be allowed. These transplants are expensive to perform, and the risk of animal diseases being transmitted to humans cannot be ruled out. It should be possible to solve the shortfall of organs available for transplant by persuading more people to carry organ donor cards. A human organ must give a human being a better chance of survival.
Exercise 2-9 2. The United States must rapidly reduce its enormous st
ockpile of nuclear weapons. After all, the United States is now the only real superpower, and there is no country competing with the United States in a nuclear arms race. And besides, maintaining a large nuclear weapon is enormously expensive-and we could use the money for better purposes, such as health care. And finally, we cannot really discourage other countries from developing and testing nuclear weapons as long as we hold many nuclear weapons ourselves: It make us look like hypocrites ( 伪君子 ) to say that they should not test nuclear weapons while we hold on to thousands of them.
Exercise 2-9 3. The recent outbreak of dizziness and nausea among Y
SU students was caused by lawn chemicals used on the lawn between Cushwa and DeBartolo. Lawn chemicals must have been the problem, because the lawn was sprayed with herbicides very early on Tuesday morning, and all of the students who became ill attended Professor Ryle’s Philosophy 697class, which was held that Tuesday morning on the lawn between Cushwa and DeBartolo.
Exercise 2-9 4. We should have very high inheritance taxes on all large
fortunes. After all, a large inheritance tax is the only way to prevent enormous wealth from being concentrated in the hands of a few people. And when wealth becomes concentrated in the hands of a few people, that corrupts our democratic process, because great wealth makes it possible for some people to exert great influence over elections as well as over elected officials through large massive campaign contributions. And it is vital to the good of all of us that we maintain a democracy, and prevent power from falling into the hands of a wealthy elite, because when a wealthy elite gain political power they use it for their own benefit and not for the benefit of all the people. Therefore, we should have very high inheritance taxes on all large fortunes.
2-9-5 Assumption: their use and abuse Legitimate assumption When I drive through a green light I assume that the
drivers for whom the light is red will stop. When I read a scientific report, I assume that the
scientist has not deliberately faked the reported data. When scientists do research, they operate from many
givens that are not brought into question by that particular research project, such as the speed of light?
2-9-6 Legitimate assumption In fact, when we make an argument, it is no doubt that we
should depend on well-known, credible assumptions. Both sides in an argument believe them, and should not argue whether they are really true or not.
Exactly, in order to make a direct or simple discussion on a particular issue, we need many legitimate assumptions.
The disturbed question is that, however, how to pick out the assumption underlying an argument, and how to judge its legitimateness or illegimateness.
2-9-7 Enthymemes( 省略三段论 ) Premises:
Total contains 100% of recommended daily allowance of nine vitamins and iron, and raisin bran contains only 25%.
Conclusion:
Total is more nutritious than raisin bran.
(1) If you eat all that, then I’m the queen of Sheba. Undoubtedly, (1) is not a argument but a statement. But
in a special background, (1) Can be acted as an argument.
(1) If you eat all that, then I’m the queen of Sheba.
(2) surely, I’m not the queen of Sheba.
Therefore, (3) you can’t eat all that.
2-9-8 Enthymemes( 省略三段论 )
2-10 Necessary and sufficient conditions If you are serving as a jury member (in North
Carolina) to find the defendant guilty of breaking and entering trial, the judge’s instructions will probably include the following:
Now I (the judge) charge that for you [the jury] to find the defendant guilty of breaking and entering, the State [the prosecution] must prove four things beyond a reasonable doubt.
(1) that there was either a breaking (which simply means the opening or removal of anything blocking entry) or an entry (walking or reaching in would be an entry) by the defendant.
(2) the state must prove that it was a building that was broken or entered.
(3) that the owner or tenant did not consent to the breaking or entering.
(4) that at the time of the breaking and entering, the defendant intended to commit some specific felony.
2-10-1 Necessary and sufficient conditions
2-10-3Necessary conditions Now when we (the jury) return to a verdict of guilt? What is the necessary conditions of the defendant guilty of
the breaking and entering? What is the sufficient conditions of the defendant guilty
of the breaking and entering? Each of the four conditions is a necessary condition for
finding the defendant guilty of breaking or entering. Taken altogether, they are sufficient for finding the defendant guilty of breaking or entering.
2-10-4 The guilty of gambling The state must prove one of two things beyond a
reasonable doubt: (1) that the defendant bet monkey on a game of
chance. (2) that the defendant played at a game of chance
because monkey was being bet on it. Then, What is the necessary conditions and sufficient
conditions of the defendant guilty of the breaking and entering?
2-10-5 Guilt or not guilty Beatrice (one of the jurors) argues that the verdict must be
not guilty: I am convinced that the defendant was in the alley where
the dice game was taking place, and he was betting monkey on it. But the game was broken up by the police before he ever had his turn at rolling the dice. There is really no evidence that he ever held the dice in his hand, and certainly no game at all. And since there is at least a reasonable doubt about whether he played the game, we can’t find him guilty of gambling.
2-10-6 Necessary conditions and sufficient conditions
“If A, then B” is true, then A is a sufficient condition of B.
For example: “ if you say sorry to me, then I will forgive your rudeness” is true, then “you say sorry to me” is a sufficient condition of “I will forgive your rudeness”.
“B, only if A” is true, then A is a necessary condition of B.
For example: “I arrive at the classroom on time, only if I am not ill” is true, then “I am not ill” is a necessary condition of “I arrive at the classroom on time”.
2-10-7 How to distinguish necessary conditions from sufficient conditions Sufficient conditions: “AB” For any conditional statement, if it asserts that once A
is satisfied (A is true), then B must follows as a consequence (then B must be true ). At this time, we call A is a sufficient condition of B. (slogan1: if A is true, then B must be true)
Necessary conditions: “AB” For any conditional statement, if it asserts that only if
A is true, “B is true” is then possible, that is, B must be false when A is false (slogan2: if A is false then B must be false). at this time, we call A is a necessary condition of B.
2-10-8 Choosing a proper answer and write in the blank
(A) not necessary but sufficient ，(B) necessary but not sufficient ，(C) necessary and sufficient ，(D) not necessary and not sufficient ：(1)p (x-1)(x+2)=0 is __∶ condition of q x=-2.∶(2)p x∶ ＞ 5 is __ condition of q x∶ ＞ 3.
(3)p 0∶ ＜ x ＜ 5 is __ condition of q∶ ｜ x-2 ｜＜ 3.
(4)p x≤2 is __ condition of q x∶ ∶ ＜ 2.
2-10-9 Alternative form “if A, then B” equals to “only if B, then A”.
“A is a sufficient condition of B”
Slogan1: if A is true, then B must be true.
Now B is false,
therefore, A must be false . that is, “A must be false when B is false” (slogan2). So, B
is a necessary condition of A. Attention: “A is a sufficient condition of B” equals to “B
is a necessary condition of A”.
2-10-10 Conclusion:(1) “A is true” “B must be true” (that is, A is a sufficient condition of
B)
(2) “A must be false” “B is false”(that is, B is a necessary condition of A)
Exercise 2-10: For these cases, look back at the conditions for
breaking or entering, and tell whether the following testimony would count for or against conviction on charges of breaking or entering.
1. George is charged with breaking or entering into Mary’s apartment and stealing her television set. Mary is testifying: “Sure, I told George he could come in and watch the football game on my TV while I was at work—in fact, I told him to have a beer and make himself at home. But I certainly didn’t tell him he could steal my TV set and sell it!
Exercise 2-10: 2. Jim is charged with breaking or entering and theft of Joe’s lawnm
ower( 剪草机 ). Joe is testifying: “look, I saw the guy with my own eyes. I was sitting in the den watching Monday Night Football. The outside light was on, and I happened to glance out the window as Jim came sneaking into the yard. He broke the lock on the back gate of the fence and then uncover the lawnmower and rolled it away.”
3. Mary is charged with breaking or entering a store with intention to stealing a TV set. Mary is testifying: “OK, so I did crawl in through the window. But I didn’t break the window. That window has been broken for over a month. I just stuck my hand in and move the latch and raised the window. I never broke anything.”
Exercise 2-11: Please determine which one is the sufficient
condition of another one.
1. Wages will increase only if the budget is balanced.
2. Without good friends, happiness is impossible; but even good friends cannot guarantee happiness.
3. Lots of teams with great quarterbacks never win the Super Bowl; but no team can win the Super Bowl without a great quarterback.
4. You will pass the exam if you studied all weekend.
5. You will pass the exam only if you studied all weekend.
Exercise 2-11: Please determine which one is the sufficient
condition of another one.
5. You must have dreams in order to change the world. 6. if Tiger Woods putts well, he will beat me at golf.
7. You’ve got to see it to believe it.
8. I'll play tennis if the sun shines.
