(完整版)LogicalFallacies逻辑谬误

1、logic (part four)fallaciesarguments, like men, are often pretenders.platowhat are fallacies?what are fallacies?fallacies are defects that weaken arguments.by learning to look for them in your own and others writing, you can strengthen your ability to evaluate the arguments you make, read, and hear.

2、two special notes about fallaciestwo special notes about fallaciesfallacious arguments are very, very common and can be quite persuasive, at least to the casual reader or listener. you can find dozens of examples of fallacious reasoning in newspapers, advertisements, and other sources. there are man

3、y different kinds of fallacies with different names.argument from ignorancedefinitiondefinitionargument from ignorance asserts that a proposition is true because it has not been proved false, or that it is false because it has not been proved true.in science and logic, we must verify the truth or fa

4、lsehood of propositions; before that, nothing can be asserted.in jurisprudence, however, there is an exception: a person is always regarded as innocent before he/she is proved guilty.examplesexamplesyou cant prove that god exists. therefore he doesnt exist.you cant prove that god doesnt exist. there

5、fore he exists.the story of galileohasty generalizationdefinitiondefinition making assumptions about a whole group or range of cases based on a sample that is inadequate (usually because it is atypical or just too small). stereotypes about people (“pilot students are handsome, grad students are nerd

6、y, etc.) are common examples of hasty generalization. exampleexamplemy roommate said her philosophy class was hard, and the one im in is hard, too. all philosophy classes must be hard! two persons experiences are, in this case, not enough on which to base a conclusion. smoking causes cancer because

7、my father was a smoker and he died of lung cancer. tiptipask yourself what kind of sample youre using:are you relying on the opinions or experiences of just a few people, or your own experience in just a few situations? if so, consider whether you need more evidence, or perhaps a less sweeping concl

8、usion. notice that in the previous example, the more modest conclusion some philosophy classes are hard for some students would not be a hasty generalization. accidentdefinitiondefinitionwhen we apply a generalization to individual cases that it does not properly govern, we commit the fallacy of acc

9、ident.almost every good rule has appropriate exceptions; we argue fallaciously when we reason on the supposition that some rules apply with universal force.accident is the opposite of false generalization.exampleexamplei am sure their ambassador will be reasonable about the matter. after all, man is

10、 a rational animal.man is a rational animal. thats true, because we have reason. but that does not mean all men behave rationally under all circumstances.“all generalizations are false, including this one.”mark twainfalse cause/post hoc (假性因果)definitiondefinitionassuming that because b comes after a

11、, a caused bof course, sometimes one event really does cause another one that comes later.for example, if i register for a class, and my name later appears on the roll, its true that the first event caused the one that came later. but sometimes two events that seem related in time arent really relat

12、ed as cause and effect. that is, correlation isnt the same thing as causation.examplesexamplespresident jones raised taxes, and then the rate of violent crime went up. jones is responsible for the rise in crime.the increase in taxes might or might not be one factor in the rising crime rates, but the

13、 argument hasnt shown us that one caused the other. a flood happened after the comet appeared; therefore, the comet caused the flood.misunderstanding of the lunar eclipsetipstipsto avoid the post hoc fallacy, the arguer would need to give us some explanation of the process by which the tax increase

14、is supposed to have produced higher crime rates. thats what you should do to avoid committing this fallacy: if you say that a causes b, you should have something more to say about how a caused b than just that a comes first and b comes later! weak/false analogy (错误类比)definitiondefinitionmany argumen

15、ts rely on an analogy between two or more objects, ideas, or situations. if the things that are being compared arent really alike in the relevant respects, the analogy is a weak one, and the argument that relies on it commits the fallacy of weak analogy. exampleexampleguns are like hammerstheyre bot

16、h tools with metal parts that could be used to kill someone. and yet it would be ridiculous to restrict the purchase of hammersso restrictions on purchasing guns are equally ridiculous.while guns and hammers do share certain features, these features (having metal parts, being tools, and being potent

17、ially useful for violence) are not the ones at stake in deciding whether to restrict guns. rather, we restrict guns because they can easily be used to kill large numbers of people at a distance. this is a feature hammers do not shareitd be hard to kill a crowd with a hammer. thus, the analogy is wea

18、k, and so is the argument based on it. examplesexamplesmind and rivers, can be both broad. it is a known fact that the broader the river, the shallower it is. therefore it must be true, that the broader the mind is, the shallower it is. employees and nails are the same. as it is necessary to hit nai

19、ls on the head in order to make them work, the same must be done with employees. tiptipidentify what properties/attributes are important to the claim youre making, and see whether the two things youre comparing both share those properties. this shows the importance of relevance.appeal to inappropria

20、te authority(诉诸不当权威)definitiondefinitionoften we add strength to our arguments by refer-ring to respected sources or authorities and explaining their positions on the issues were discussing. this is quite proper and even encouraged in academic research.if, however, we try to get readers to agree wit

21、h us simply by impressing them with a famous name or by appealing to an authority who has no special competence in the sphere concerned, we commit the fallacy of appeal to inappropriate authority. exampleexamplewe should abolish the death penalty. many respected people, such as actor mr. handsome, h

22、ave publicly stated their opposition to it.the most blatant examples of misplaced appeals to authority appear in advertising “testimonials.”tipstipsthere are two easy ways to avoid committing appeal to inappropriate authority: first, make sure that the authorities you cite are experts on the subject

23、 youre discussing;second, rather than just say dr. authority believes x, so we should believe it, too, try to explain the reasoning or evidence that the authority used to arrive at his or her opinion. it also helps to choose authorities who are perceived as fairly neutral or reasonable, rather than

24、people who will be perceived as biased. ad populum /appeal to people(诉诸群众)definitiondefinitionthe arguer takes advantage of the desire most people have to be liked and to fit in with others and uses that desire to try to get the audience to accept his or her argument. one of the most common versions

25、 is the bandwagon fallacy (主流思想谬误), in which the arguer tries to convince the audience to do or believe something because everyone else (supposedly) does.it is also very commonly used in advertisements.exampleexamplegay marriages are just immoral. 70% of americans think so.why are so many people att

26、racted by the pontiac grand prix? it could be that so many people are attracted by the grand prix becauseso many people are attracted by the grand prix!tiptipmake sure that you arent recommending that your audience believe your conclusion because everyone else believes it, all the cool people believ

27、e it, people will like you better if you believe it, and so forth. keep in mind that the popular opinion is not always the right one!“the fact that an opinion has been widely held is no evidence whatsoever that it is not utterly absurd; indeed, in view of the silliness of the majority of mankind, a

28、wide-spread belief is more likely to be foolish than sensible.”bertrand russellsb战胜天才的办法：战胜天才的办法：sb可以随时叫可以随时叫100个个sb来证明来证明sb是对的，而天才怎么也叫不是对的，而天才怎么也叫不到到100个天才来证明天才是正确的。个天才来证明天才是正确的。 appeal to pity(诉诸怜悯)definitiondefinitionthe argument tries to convince the audience of something by arousing its sense o

29、f pity and mercy.this is most commonly used at law courts.the fact that someone is pitiful does not make his/her wrong deeds right.exampleexampleim quite sure i was driving below the speed limit, officer; i had my eye on the speedometer. ive had tickets before, and if you give me one now, it will pr

30、obably cost my drivers licenseand if i lose my license ill lose my job. dont you think a warning would be enough?why didnt you drive slowlier at the first place?可怜之人必有可恨之处。可怜之人必有可恨之处。exampleexamplethe absurdity of appeal to pity is best ridiculed by a joke: a teenager is accused of murdering his fat

31、her and mother with an axe; confronted with overwhelming proof of his guilt, he pleaded for leniency on the grounds that he is an orphan.appeal to force(诉诸武力)definitiondefinitionthe argument coerces the audience into accepting the conclusion by resorting to threat.the famous proponent of this fallac

32、y is thrasymachus, for whom “might is right.”the appeal to force is the abandonment of reason.秀才遇到兵，有理说不清。秀才遇到兵，有理说不清。exampleexample“socrates, i think that you are too ready to speak evil of men: and if you will take my advice, i would recommend you to be careful. perhaps there is no city in which i

33、t is not easier to do men harm than to do them good, and this is certainly the case at athens, as i believe that you know.”plato, menofalse dichotomy 错误二分法 definitiondefinitionin false dichotomy, the arguer sets up the situation so it looks like there are only two choices. the arguer then eliminates

34、 one of the choices, so it seems that we are left with only one option: the one the arguer wanted us to pick in the first place. but often there are really many different options, not just two.exampleexamplecaldwell hall is in a bad shape. either we tear it down and put up a new building, or we cont

35、inue to risk students safety. obviously we shouldnt risk anyones safety, so we must tear the building down.tiptipexamine your own arguments: if youre saying that we have to choose between just two options, is that really so? or are there other alternatives you havent mentioned? if there are other al

36、ternatives, dont just ignore themexplain why they, too, should be ruled out. although theres no formal name for it, assuming that there are only three options, four options, etc. when really there are more is similar to false dichotomy and should also be avoided.begging the question 乞求窃取论点definition

37、definitiona complicated fallacy, it comes in several forms and can be hard to detect. basically, an argument that begs the question assumes the truth that it tries to prove, in the effort to prove it. it is circular. the argument either relies on a premise that says the same thing as the conclusion

38、or reasons in a circular way.simplified formsa, therefore a.(a, therefore b.) b, therefore a.example 1 example 1 active euthanasia is morally acceptable. it is a decent, ethical thing to help another human being escape suffering through death. premise: it is a decent, ethical thing to help another h

39、uman being escape suffering through death.conclusion: active euthanasia is morally acceptable.if we translate the premise, well see that the arguer has really just said the same thing twice: decent, ethical means pretty much the same thing as morally acceptable, and help another human being escape s

40、uffering through death means active euthanasia. so the argument is really saying “active euthanasia is morally acceptable because active euthanasia is morally acceptable.” it begs the question.more examplesmore examplesto allow every man unbounded freedom of speech must always be, on the whole, adva

41、nta-geous to the state; for it is highly conducive to the interests of the community that each individual should enjoy a liberty, perfectly unlimited, of expressing his sentiments.god exists because this is what the bible says, and the bible is reliable because it is the words of god.i am an honest

42、man because frank says so. how can we trust frank? simple. i will vouch for him.the story of humecomplex questiondefinitiondefinitiona complex question is a question which presupposes the truth of some assumption(s) buried in that question.exampleexample“why are private enterprises much more efficie

43、nt than government-owned enterprises?”assumption: private enterprises are much more efficient than any government-owned enterprisesexampleexamplecomplex questions are often used at court by shrewd lawyers to mislead the questioned person.“the figures seem to indicate that your sales increased as a r

44、esult of these misleading advertisements. is that correct?”“they did not!”“but you do admit, then, that your advertising was misleading. how long have you been engaging in practices like this?”when the question is complex, and its presuppositions are to be denied, they must be denied individually.ex

45、ampleexampleare you in favor of increased governmental service and higher taxes? if you are, those whose taxes are already too high will vote against you. if you are not, those who need more services from the government will vote against you. in no case can you hope to win the election.ad hominem /a

46、gainst the person(人身攻击的谬误)definitiondefinitionthe ad hominem (against the person) fallacies focus our attention on people rather than on arguments or evidence. in an ad hominem argument, the arguer attacks his or her opponent instead of the opponents argument. there are two forms of arguments ad hom

47、inem.abusive ad hominemcircumstantial ad hominemabusive abusive ad hominemad hominemabusive ad hominem is launched directly against persons, seeking to discredit or defame them.that the arguer has a bad character does not necessarily mean the argument is bad.exampleexampleandrea dworkin has written

48、several books arguing that pornography harms women. but dworkin is an ugly, bitter person, so you shouldnt listen to her. circumstantial circumstantial ad hominemad hominemwhen the attack is indirectly against the persons, suggesting that they adopt their view chiefly because of their special circum

49、stances or interests, it is called a “circumstantial ad hominem.”that someone has adopted a view because of his/her special circumstances or interests does not necessarily mean that view is wrong.examplesexamplesim afraid, mr. black, that you are showing tolerance to homosexual marriage only because

50、 you want to win more public support for your campaign.“you are hurt. you should quit the game and go to the doctor.”“yeah, so that you can be the champion.”irrelevant conclusion/non sequiurdefinitiondefinitionthe premises of an argument do not support the conclusion.in other words, the conclusion d

51、oes not follow from the premises; or, we can say, the premises “miss the point.”exampleexamplethe seriousness of a punishment should match the seriousness of the crime. right now, the punishment for drunk driving may simply be a fine. but drunk driving is a very serious crime that can kill innocent

52、people. so the death penalty should be the punishment for drunk driving. exampleexampleall children should have ample attention from their parents. parents who work full-time cannot give ample attention to their children. therefore, mothers should not work full-time.fallacy of compositiondefinitiond

53、efinitiontwo types of fallacies of compositionfirst type: reasoning from the attributes of the parts of the whole to the attributes of the whole itselfsecond type: reasoning from the attributes of the members of a collection to the attributes of the collection itselfexamples: first typeexamples: fir

54、st typesince every part of a certain machine is light in weight, the machine “as a whole” is light in weight.since every scene in a play is a model of artistic perfection, the play as a whole is artistically perfect.since every player in the team is good, the team as a whole is good.the whole does n

55、ot necessarily partake of the attributes of the individual parts because the problem of organization and structure is involved.你的眉毛、眼睛、耳朵、鼻子、嘴巴都长得你的眉毛、眼睛、耳朵、鼻子、嘴巴都长得很漂亮，但是一起放在你的脸上就不对了。很漂亮，但是一起放在你的脸上就不对了。examples: second typeexamples: second typesince a bus uses more gasoline than a car, all buses us

56、e more gasoline than all cars.since a college students may enroll in no more than six courses each semester, all college students may enroll in no more than six courses each semester.the second type is very confusing, because phrases such as “all college students” can be used both “distributively,” meaning “all individual colleg