曼哈顿FoV. CR笔记目录1.All about the Argument (1)Sound argument vs. valid argument (1)On the GMAT (2)The arguer’s job and your job (2)List of the twelve flaws (2)Details of the twelve flaws (3)A. Unjustified Assumptions (3)B. Causation Errors (4)C. Comparison Errors (5)D. Math Errors (6)E. Communication Errors (7)Find the gaps in arguments (7)2.Decoding the Question Stem and Stratege (8)1. All about the ArgumentSound argument vs.valid argumentEvery complete argument has two components written down on paper:• Premises—supporting statements• Conclusion— the main point or biggest claim of the argumentA sound argument is successful on every level: the premises are true, and the conclusion logically follows from the premises. When a conclusion follows logically from true premises, that conclusion is therefore true.A valid argument is one in which the conclusion follows logically from the premises—but the premises may or may not be true. In a valid argument, if the premises are true, then the conclusion will also be true.In a good, valid argument, the premises lead to the conclusion in a direct way. They provide enough evidence to guarantee the truth of the conclusion (which is occasionally implied rather than stated explicitly).On the GMATWhile soundness is the goal in real-life reasoning, GMAT questions tend to be more about validity.So, on the GMAT, avoid challenging the truth of the premises themselves.Focus on whether the argument is valid.The arguer’s job and your jobPeople’s brains are desi gned to make connections and to go beyond the arguer’s conclusi on.On the GMAT, however, you should note the speaker’s conclusion precisely.It’s the job of the arguer to prove his or her case to you by building a sound argument backed by appropriate evidence. Your job is simply to recognize flaws and omissions.List of the twelve flawsThese flaws overlap somewhat; it doesn’t really matter.This isn’t a full course in formal logic. What’s more important is that you understand the typicalversion of each flaw. This way, you can spot any of them on the test.A. Unjustified Assumptions1. Assumes Shared Beliefs2. Draws Extreme Conclusion3. Assumes Skill and/or Will4. Uses Vague or Altered Terms5. Assumes Signs of a Thing = Thing ItselfB. Causation Errors – 1. causal oversimplification6. Mixes up Correlation and Causation7. Assumes the Future = the Past – 4. all things are equal8. Assumes the Best Means SuccessC. Comparison Errors9. Has Selection Bias(Unrepresentative sample, survivor bias, ever-changing pool) – 6. Surveyis doubtful10. The Troubled Analogy – 3. false analogyD. Math Errors11. Confuses the Quantities (percent, rates, ratios)E. Communication Errors12. Missing the PointDetails of the twelve flawsA. Unjustified AssumptionsAn argument with this sort of flaw requires an unspoken and unsupported premise—that is, the authoris depending on a premise that he or she didn’t write down and hasn’t proven. Thus, the conclusioncan’t be validated unless the assumption can be proven.1. Assumes Shared BeliefsThe arguer assumes that the listener will share certain basic beliefs—some of which are mere impressions,prejudices, and so on.The speaker’s argument depends on the idea that ―teenagers under 16 are more likely to make theaters dirty and to damage the facilities,‖ the speaker didn’t even bother to write that—and he or she certainly didn’t prove it.D on’t take anything for granted, and don’t bring in outside ideas.It’s the arguer’s job to prove such an assumption. It’s your job to notice that thearguer hasn’t done so.2. Draws Extreme ConclusionThe conclusion uses language so extreme that the premises cannot justify that conclusion:Watch out for these extreme words: only, never, always, cannot, certainly, obviously, inevitably, most, least,best, worst.Theword best is quite extreme. Jogging is the best method ever? Better than swimming, tennis, and a millionother things? Even if you prove that jogging is better in some respect than stationary bicycling, allyou can say is that jogging is better than one other activity, not that it’s the best.Keep in mind that even a perfectly reasonable argument can be destroyed by too strong a conclusion.3. Assumes Skill and/or WillFor people to do something, they have to be able to do it, and they have to want to.Some arguments give you one piece but not the other.But both skill and willare necessary.4. Uses Vague or Altered TermsJust as you are on the lookout for extreme language, you’re also on the lookout for vague or altered language throughout the argument.Recall the People who jog argument:What on earth does it mean to exercise the same amount as someone who is jogging 10 miles? Does itmean biking for the same amount of time or the same distance? The same number of calories burned?It’s much faster to ride 10 miles on a stationary bike than to jog 10 miles, so if the arguer means thatthe distances are the same, then there’s another reason (besides the author’s conclusion) that the joggershave less heart disease: they are exercising more hours per week. Exercise the same amount is overlyvague. Question any term that’s insufficiently precise.Likewise, any change in terms through the course of the argument should make you arch an eyebrow. Whether the terms become more general or more specific, the argument now has a fissure in its logic.5. Assumes Signs of a Thing = Thing ItselfDon’t confuse external signsand reality. Quite often, the signs can be misleading.A false reporting effect is especially acute when people have an incentive (such as money) to over-report,or an incentive (such as fear or laziness) to under-report.For instance, reports of crimes such as litteringand jaywalking are infrequent—that doesn’t mean people aren’t committing those crimes all thetime. Reports of whiplash from car accidents, however, tend to be highly inflated (at least in the U.S.),since victims are often in a position to gain money from insurance companies. Reports of workplaceharassment or other improper working conditions may be less frequent than actual incidents if workersfear losing their jobs.Another common variation on this problem assumes that, because a law exists, people must be followingit. A law is not the same as compliance with a law.B. Causation ErrorsMany conclusions assert that something is the cause of something else, usually without the word ―cause‖ itself.Look closely at the verb: cause, make, force, lead to, prevent, protect, increase, decrease, reduce.Alsolook at infinitives (e.g. to reduce), which often indicate goals. The achievement of goals requires causation.6. Mixes up Correlation and CausationIf two things occur together (correlation), you can’t automatically concludethat a particular causal model is at work. Likewise, if X happenedshortly after Y, you cannot necessarily conclude that X was caused byY.To review: If X and Y seem to be correlated, and then there are four possibilities:(1) X causes Y.(2) Y causes X.(3) Z (some other phenomenon) causes both X and Y.(4) It’s an accident; you don’t have all the data.Logically, you cannot pick one of the four without eliminating all of the other three.On the GMAT, you’ll never be able to eliminate all three alternatives. But eliminating even one will strengthen your case.7. Assumes the Future = the Past8. Assumes the Best Means SuccessSometimes, a variety of options are available to solve a problem, but none of those options are very likelyto succeed. This does not affect whether an option can be considered the best, whether it had somebeneficial effect, or whether it could still be the best solution to a less severe version of the problem.For instance, if a new CEO is hired to try to rescue a company on the brink of bankruptcy, even thebest possible effort simply may not be enough. If someone dies of a terrible disease that does not meanthat he did not receive optimal medical care.Sometimes even the best thing fails.C. Comparison ErrorsThe assumption typically being that the two things are similar enough in the important ways to be compared.9. Has Selection BiasWhenever you compare two groups, you have to make sure that the two groups are legitimately comparable.So the membership of each group has to be selected appropriately. This is particularly tricky whenthe two groups seem comparable—for instance, when they are both drawn from the same population.There are a few variations of selection bias:9.1 Unrepresentative SampleWouldn’t that sample of customers be biased toward people who like you? After all, they filled out along survey for free. The potential for self-selection bias is strong here.Some customers who filled out a long survey for free said that they love our company.So our customers love our company.9.2 Survivor BiasHere, it is likely that those who lived to be 100 did so in part by not smoking, and that plenty of peopleborn 100 or more years ago did smoke and did not live to be 100.A survey of living people over 100 showed lower rates of cigarette smoking thanwere shown inevery other age group age 15 and up. Therefore, smoking is on therise.9.3 Ever-Changing PoolFive years ago, people opposed the new dorm, and now 80% of respondents to a poll like the dorm.Are the poll respondents the same population as the voters? Maybe the poll was conducted on or nearcampus; a high percentage of students in the poll would certainly skew results.A petition is circulating in Capital City opposing the building ofa new sportscenter at StateUniversity, on land now occupied by abandoned strip malls. Fiveyears ago, many city residents opposed the building of the new State Universitydormitory complex, yet in a poll this year, 80% of respondents said that buildingthe dormitory complex had been a good idea. If the people who currently opposethe new Sports Center are patient, they will change their minds.10．The Troubled AnalogyThere’s nothing wrong with a good analogy, but analogies in GMAT arguments are never good.Everytime you make an analogy, you’re saying that something is like something else— except that it isn’texactly like that, or you’d just be talking about the original topic.It’s your job to point out that the arguer has not established enoughsimilarities between the two objects to draw an effective analogy between them.D. Math ErrorsTo validate this claim, even just for one cat owner, you would need to know 1) how much more the catfood costs than the kind that the cat owner currently buys, 2) how much time the cat owner spendscleaning up hair, and 3) the monetary value of the cat owner’s time. That’s substantial!According to a recent study, cats that eat Premium Cat Food have healthier coatsand shed less hair than those that don't. While Premium Cat Food costs more, thetime saved cleaning up pet hair from furniture and rugs makes Premium Cat Fooda wise choice for cat owners.11. Confuses the QuantitiesCeladon, a new therapy for the treatment of addiction to the illegal drug taro Caine,has been proven effective in a study centered around Regis Hospital in thewestern part of the state of New Portsmouth. The study involved local taro Caineaddicts who responded to a newspaper ad offering free treatment. Participantswho received celadon and counseling were 40% more likely to recover thanwere patients assigned to a control group and who received only counseling.Conventional therapies have only a 20% recovery rate. Therefore, the best way toreduce deaths from taro Caine overdose throughout all of New Portsmouth would be to fund celadon therapy for all taro Caine addicts.40% certainly looks like a higher number than 20%. However, the 20% is an actual recovery rate for conventional therapies.The 40% is a percent increase on an unknown figure— the recovery rate of the control group. You haveno way to compare this to an actual 20% recovery rate. For instance, what if the control group hada 50% recovery rate? Then the cetadone group would have 70% recovery rate (1.4 x50). But what ifthe control group had a 1% recovery rate? Then the cetadone group would have a 1.4% recovery rate,making it much less successful than conventional therapies.Notice that you are mentally plugging innumbers to test a couple of valid cases at the extremes. Be ready to do the same.In short, if any numbers or numeric relationships are presented in an argument, determine whether theyare being cited in a logical way.A few other standard mathematical relationships show up in Critical Reasoning as well:Rate x Time = DistanceProfit = Revenue - Costs(Dollars per Hour) x Hours = DollarsE. Communication Errors12. Missing the PointSome people say we should consume less oil to lower our dependence on suppliesfrom politically unstable regions. But no one has yet proven the link betweenoil consumption and climate change.This type of flaw is very common when people argue over causes they feel deep emotions about.Find the g aps in a rgumentsFor each argument, draw the arrows and find out the gaps.There are gaps much larger than othersStudies have shown that students who go without lunch do poorly in school.Many students are hungry in school because they cannot afford to pack or buylunch. Therefore, a program of free school lunches should help these studentsperform at grade level.You might diagram it in this way:Note that the order of the premises has been slightly rearranged to put them in time order. Start at the beginning. Students can’t afford lunch, so they don’t eat lunch, so they do poorly in school. Is there agap?While it certainly does seem reasonable that a lack of food would contribute to poor academic performance,the gap here is related to Causation. Yes, the students are hungry and they are doing poorly,butis the hunger really causing the poor performance? How much of the poor performance is it causing?Could there be some other factor contributing to the poor performance?The second gap is much larger, though. Free lunch will help students perform at grade level? That’s quiteambitious. Unfortunately, there are entire schools in which the majority of children perform far belowgrade level, and it is doubtful that lunch alone would fix the entire problem.2. Decoding the Question Stem and StrategyGMAT Question stems fall into a few broad categories:✓Questions about Assumptions✓Questions about Evidence✓Questions about StructureIt can be helpful to categorize each question as involving Assumptions, Evidence, or Structure. Themost important thing is that you understand what the question specifically wants you to do. It is alsorecommended that you write down a brief note about the question as a reminder.Just remember tomaintain good strategy:✓read the question stem first,✓diagram the argument,✓anticipate the answer,✓anduse process of elimination.An example:While many people think of the lottery as a harmless way to have fun and possiblywin somemoney, buying lottery tickets is a form of gambling. Therefore, publicofficials shouldn't buylottery tickets.Which of the following, if true, would most strengthen the conclusion?You can mentally dismissthat part and think of the argument this way:Buying lottery tickets is a form of gambling. Therefore, public officials shouldn't buylotterytickets.Diagram the argument:Express the missing assumption yourself before proceeding. In general, identify assumptions before reading the answer choices, so you don’t get tricked by evil wrong ans wers that are there to distractyou.K eep in mind that you’re not just looking for a choice that supports the statement. You are looking specifically for a choice that supports this conclusionin the context of this argument.You need an answer that links the premise to the conclusion.If you’re having trouble withyour original argument, translate it to a simpler, crazier version. It will be easier to figure out the assumption.Weight lifting is a form of exercise. Therefore, public officials shouldn't lift weights.Then go back to the argument: The assumption here is Public officials shouldn't gamble. In your diagram, you would see it as PO'sshouldn't G.Some other points from the comments of the exercises:✓As a correct GMAT answer will not generally insult anyone.✓Some choices seem to be trying to argue against the premise mentioned in the argument, but since wealready take the premise as a fact, these choices don’t really have an impact on the argument—surely, they might be true, but that must have already beentaken into account. On average, the fact in premise is still valid.。