Critical ThinkingLecture 4: Informal fallacies（谬误）It is easy for us to make mistakes in our reasoning because we are easily affected by psychological emotions, social and political circumstances(including our interests), and customs and public opinion, and complexity of reasoning itself.One of the purposes of this course is to learn how to avoid mistakes or fallacies in reasoning.The first thing we need to do is to identify fallacies.1. Fallacies in generalA fallacy is a defect（缺陷）in an argument that consists in something otherthan merely false premises.A fallacy that involves a mistake in reasoning is sometimes called a nonsequitur (which, in Latin, means “it does not follow”).Two kinds of fallacies: formal and informalIf an argument is unsound or uncogent, then either it has one or more false premises or it commits a fallacy, or both.A formal fallacy is one that may be identified by merely examining the form orstructure of an argument. Fallacies of this kind are found only in deductive arguments.Example of Formal FallaciesIf apes are intelligent, then apes can solve the puzzles.Apes can solve the puzzles.Therefore, apes are intelligent.This is an invalid argument.Formal fallacies are identified purely by analyzing the form.It has the following form:If P, then Q.Q.Therefore, P.Counter example:If it is a rose, then it is a flower.It is a flower.Therefore, it is a rose.Informal fallacies are those that can be detected（检测到）only by examining the content of the argument.Examples of informal fallaciesA chess player is a person.Therefore, a bad chess player is a bad person.The Brooklyn Bridge is made of atoms.Atoms are invisible.Therefore, the Brooklyn Bridge is invisible.Fallacies of Relevance（意义，关联）The common feature to all the fallacies of relevance is that the premises are logically irrelevant to the conclusion, though they might be psychologically relevant.1. Appeal to ForceThe arguer tries to get his conclusion accepted by a person or persons by threatening that person or those persons.A girl to her boyfriend: “You should buy me a diamond necklace, otherwise I willend our relationship.”Secretary to boss: I deserve a raise in salary for the coming year. After all, you know how friendly I am with your wife, and I’m sure you wouldn’t want her to find out what’s been going on between you and that sexpot client of yours.构成，提出2. Appeal to PityInstead of providing the relevant evidence or reason, the arguer tries to evoke sympathy from the audience or the reader to get his conclusion accepted.Taxpayer to judge: Your Honor, I admit that I declared thirteen children as dependents on my tax return, even though I have only two. But if you find me guilty of tax evasion, my reputation will be ruined. I’ll probably lose my job, my poor wife will not be able to have the operation that she desperately needs, and my kids will starve. Surely I am not guilty.3. The Appeal to the People (Emotion)The arguer tries to get the conclusion accepted by playing on the listeners’ or readers’ desire to be loved, esteemed, admired, valued, or accepted by others or included in a group of people.Play on/upon 利用There are direct and indirect appeal to the people.Let us concentrate on indirect appeal.The bandwagon argument风靡的活动，时尚If you don’t do such and such, so and so, you will be left behind or out of the group.Example:Of course you want to buy Crest toothpaste, because 90 percent of Americans brush with Crest.The appeal to vanity 虚荣If you do such and such, so and so, you will be admired, pursued or imitated. Example:The Few, the Proud, the Marine.The appeal to the snobbery势利态度Similar to the appeal to vanity.A Rolls-Royce [劳斯莱斯] is not for everyone. If you qualify as one of the selectfew, this distinguished classic may be seen and driven at British Motor Cars, Ltd. (By appointment only, please.)Mother to child: You want to grow up and be just like Wonder Woman, don’t you? Then eat your liver and carrots.4. Argument Against the Person (Argumentum Ad Hominem)The arguer commits this fallacy if in his argument, he directs his attention to another arguer rather than the second arguer’s argument or position.There are three kinds of such fallacy: circumstantial, abusive and tu quoqueAd hominem-abusiveThe arguer verbally abuses or attacks another arguer. (offensively or verbal abuse)Poet Allen Ginsberg has argued in favor of abolishing censorship of pornographic literature. But his arguments are nothing but trash. Ginsberg, you know, is a marijuana-smoking homosexual and a thoroughgoing advocate of the drug culture.Ad hominem-circumstantialThe arguer discredit the opponent’s argum ent by alluding to certain circumstances about the opponent.President George W. Bush argues that we should open up the Arctic National Wildlife Refuge for oil drilling. But Bush just wants to reward his rich cronies in the oil industry who got him elect ed. Thus, we can hardly take Bush’s argument seriously.Tu quoque (you too)Child to parent: Your argument that I should stop stealing candy from the corner store is no good. You told me yourself just a week ago that you, too, stole candy when you were a kid.The judge has ruled that we are not paying our employees well enough. How can this be right when the judge’s own secretary doesn’t get paid well either?5. AccidentOne commits Accident if one misapplies (incorrectly applies) a general principle to a specific case.Dogs have four legs. Fido just had one of his legs amputated. So, Fido is not a dog any more.6. Straw ManThis fallacy is committed when an arguer distorts歪曲an opponent’s对手，竞争者argument for the purpose of more easily attacking it.Mr. Goldberg has argued against prayer in the public schools. Obviously Mr.Goldberg advocates atheism. But atheism is what they used to have inRussia. Atheism leads to the suppression of all religions and the replacementof God by an omnipotent state. Is that what we want for this country? I hardly think so. Clearly, Mr. Goldberg’s argument is nonsense.7. Missing the point (Irrelevant 不相关的Conclusion)The premises are supposed to lead to one conclusion but a totally different conclusion is drawn.Crimes of theft and robbery have been increasing at an alarming rate lately.The conclusion is obvious: we must reinstate the death penalty immediately. Certainly Miss Malone will be a capable and efficient manager. She has a great figure, a gorgeous face, and tremendous poise, and she dresses veryfashionably.8. Red HerringIt is committed when the arguer diverts the attention of the reader or listener by changing the subject to a different but sometimes subtly related one.The arguer tries to draw the audience or readers off right track and then draw a conclusion on a different issue.).There is a good deal of talk these days about the need to eliminate pesticides from our fruits and vegetables. But many of these foods are essential to our health. Carrots are an excellent source of vitamin A, broccoli is rich in iron, and oranges and grapefruits have lots of vitamin C.We’ve all heard the argument that too much television is the reason our students can’t read and write. Yet, many of today’s TV shows are excellent.“Seinfeld” explores important issues facing single people, “E.R.” pres entsmedical professionals in life-and-death situations, and “60 minutes” exposes a great variety of scams and illegal practices. Today’s TV is just great!偏离轨道Fallacies of Weak InductionPremises are relevant to the conclusion but not strong enough to draw the conclusion.9. Appeal to Unqualified AuthorityAn argument commits such a fallacy if and only if the arguer appeals to the inappropriate authority that is not the expert in the subject at hand to prove the conclusion instead of relevant evidence or appropriate authority.Pianist Ray Charles says that Sinclair paints are groovy. We can only conclude that Sinclair paints are very groovy indeed.Appropriate正确的恰当的authority must meet at least two conditions:(1) The expert on the subject.(2) There is agreement among experts in that area.“Why should I be moral?” must be one of the most important issues in ethics, because professor Stephen Darwall says so, who is one of the leadingphilosophers in ethics and there are no other moral philosophers哲学家who disagree with him.In some areas such as politics, morals, and religion, there is no appropriateauthority we can appeal to. For example,Abortion (Homosexuality) is morally wrong because according to the Bible, it is wrong.10. Appeal to IgnoranceAn argument commits this fallacy if and only if when the premises state that this statement must be true because it has not been proved false or it is falsebecause it has not been proved true.Arguments are supposed to provide positive evidence. If something is incapable of being proved or disproved, we cannot use that thing to prove or disprove a conclusion.People have been trying for centuries to provide conclusive evidence for the claims of astrology, and no one has ever succeeded. Therefore, we must conclude that astrology is a lot of nonsense.Conversely,People have been trying for centuries to disprove the claims of astrology, and no one has ever succeeded. Therefore, we must conclude that astrology is true.Two exceptions(1) If qualified researchers investigate a certain phenomenon within their rangeof expertise and fail to find any evidence, then this search can constituteevidence for a conclusion.Teams of scientists attempted over a number of decades to detect the existence of the luminiferous ether, and all failed to do so. Therefore, the luminiferous ether does not exist.(2) If it is an issue of courtroom procedure:Members of the jury, you have heard the prosecution present its case against the defendant. Nothing, however, has been proved beyond a reasonable doubt. Therefore, under the law, the defendant is not guilty.No fallacy since “Nothing has been proved beyond a reasonable doubt” is what “not guilty” means in its legal sense.11. Hasty Generalization (Converse Accident)This fallacy is commited when a general conclusion is drawn from a too small sample (a few cases) or a biased sample (not representative).On our first date, George had his hands all over me, and I found it nearly impossible to keep him in his place. A week ago Tom gave me that stupid line about how, in order to prove my love, I had to spend the night with him. Men are all alike. All any of them wants is sex.12. False CauseThe connection between the premises and the conclusion depends on an imagined causal connection that does not exist.Three types of false cause: non causa pro causa (“not the cause for the cause”), “after this, therefore, because of this” and oversimplified cause.12a. non causa pro causa (“not the cause for the cause”)During the past two months, every time that the cheerleaders have worn blue ribbons in their hair, the basketball team has been defeated. Therefore, to prevent defeats in the future, the cheerleaders should get rid of blue ribbons.12b. post hoc ergo propter hoc (after this, therefore, because of this)A few minutes after Governor Harrison finished his speech on television, adevastating earthquake struck southern Alaska. For the safety of the people up there, it is imperative that Governor Harrison make no more speeches.12c. Oversimplified causeThis variety occurs when a multitude of causes is responsible for a certain effect but the arguer selects just one of these causes and represents it as if it were the sole cause.Today, all of us can look forward to a longer life span than our parents and grandparents. Obviously, we owe our thanks to the millions of dedicateddoctors who expend every effort to ensure our health.13. Slippery SlopeIt occurs when the conclusion of an argument rests upon an alleged chain reaction and there is not sufficient reason to think that the chain reaction will actually take place.It is never a good idea to permit teenagers to drive. Almost at once, they ask for the family car for a date. They have a few beers, and pretty soon they’re in the back seat having sex. The girl gets pregnant and is forced into thehorrendous decision whether to have an abortion, or to live her life as anunmarried mother.Fallacies of Presumption, Ambiguity,and Grammatical Analogy14. Begging the Question or Circular ReasoningThe fallacy is committed when the arguer creates an illusion that inadequate premises provide adequate support for the conclusion (1) by leaving out a key premise, or (2) by restating the conclusion as a premise or assuming the truth of the conclusion in the premise(s), or (3) by reasoning in a circle.The latin name for this fallacy, petitio principii, means “request for the source.”(1) Cases of leaving out a key premiseMurder is morally wrong. This being the case, it follows that abortion is morally wrong.This argument begs the question “How do you know that abortion is a form of murder?”Clearly, terminally ill patients have a right to doctor assisted suicide. After all, many of these people are unable to commit suicide by themselves.This argument begs回避the question “Just because terminally ill patients cannot commit suicide, why does it follow that they have a right to a doctor’sassistance?”(2) Cases of restating the conclusion as a premiseAnyone who preaches revolution has a vision of the future for the simple reason that if a person has no vision of the future he could not possibly preach revolution.Capital punishment is justified for the crimes of murder and kidnapping because it is quite legitimate and appropriate that someone be put to death for having committed such hateful and inhuman acts.(3) Cases for circular reasoningFord Motor Company clearly produces the finest car in the United States. We know they produce the finest cars because they have the best designengineers. This is true because they can afford to pay them more than other manufacturers. Obviously, they can afford to pay them more because they produce the finest cars in the United States.What is the difference between “Begging the question” and valid arguments? The difference depends on whether they create an illusion that inadequate premises provide adequate support for the conclusion or not.15. Complex QuestionYes or no, you have to accept my conclusion.Have you stop beating your spouse yet?Have you stopped cheating on exams?16. False DichotomyThis fallacy is committed when one of the premises is a false dichotomy or a false disjunctive statement.A dichotomy is a pair of alternatives (states, characteristics, or conditions) thatare both mutually exclusive and jointly exhaustive. X and Y are mutually exclusive if nothing can be both X and Y. X and Y are jointly exhaustive if everything must be either X or Y.Either you buy only Chinese-made products or you don’t deserve to be called a loyal Chinese. Yesterday you bought a new Toyota. It’s therefore clear that you don’t deserve to be called a lo yal Chinese.17. Suppressed EvidenceIf the argument ignores some obvious evidence against it, it commits the fallacy of Suppressed Evidence. For example,Most dogs are friendly and pose no threat to people who pet them. Therefore, it would be safe to pet the little dog that is approaching us now.18. Equivocation含糊的It is committed when the argument depends on different senses of a term. To determine whether the argument commits the fallacy, we should be able to tell it is equivocal on what term.We have a duty to do what is right. We have the right to speak out in defenseof the innocent. Therefore, we have a duty to speak out in defense of the innocent.A mouse is an animal. Therefore, a large mouse is a large animal.19. Amphiboly有歧义It is committed when the ambiguity of a statement in the argument is due to a structural or grammatical defect.One morning I shot an elephant in my pajamas. How he got into my pajamas I'll never know.John told Henry that he had made a mistake. It follows that John has at least the courage to admit his own mistakes.Difference between ambiguity and equivocationThe Great Western Cookbook recommends that we serve the oysters when thoroughly stewed. Apparently the delicate flavor is enhanced by theintoxicated condition of the diners.20. CompositionIt is committed when the conclusion of the argument depends on the erroneous transference of a characteristic from the parts of something to the whole.Hydrogen and oxygen are gases. Therefore, H2O is a gas.21. DivisionIt is committed when the conclusion of the argument depends on the erroneous transference of a characteristic from whole to parts of something.According to a recent survey, 20 % of married women have an affair with a man other their husbands. Therefore, every married woman must sleep with a man other than her husband twice every ten days.。