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三、归纳题的题型差异 |
逻辑原文在题目的上方，称为“上”，选项在题目下方，称为“下”，“上推下”为归纳题。归纳题的普遍解法是不可从文章中总结归纳得出新元素、新事件，或新程度。但同属“上推下”出题形式，归纳题之间也会有部分差异，应看清题目所问，从提问来分析正确答案的方向。
“上推下”题型可细分为：
1. 必定是真类考题（must be true）
2. 最能支持类考题（most strongly support）【推理题（infer）】
3. 其他形式“上推下”题
4. 归纳题中的“数学题”
解读： 如果出题方式是“If the information given as facts above is true, which of the following must also be true”，那么选项一定可以从文章中推测出来，“must be”提示不允许有反例出现。
如果出题方式是“The information above best supports which of the following hypotheses”（文章最能支持下列哪种假说），需不需要这个假说里的词汇全部由文章内容所组成？当然不需要。类似题型的答案一定是选项描述事件和原文的事件一致，但是允许出现新词汇，只要选项的整体意思能从原文推出即可。
“下面哪个选项可以被推理出来”类问题的答案允许有反例存在，但是不能选择无法判断的事件，答案可以是原文中描述事件的一个子集。
其他类的“上推下”考题较少，如果出现，考生们也要注意和一般归纳题的解题差异。“If the statements above are true, then it is also possible that...”问哪个选项可能对，只要和原文不冲突的选项都可能对，所以类似这样的题型就不能再使用发现新词汇就排除特定选项的方法了。
出题方会如何灵活地出题无法预测，总之考生们应注意从题目的问法上去分析，千万不要固化自己的思维。上述三种题型中，只有第一种需要找到一个没反例的选项，其他题型找一个相对最能推出，但不需要百分之百没有反例的选项。
例1 The theory of military deterrence was based on a simple psychological truth, that fear of retaliation makes a would-be aggressor nation hesitate before attacking and is often sufficient to deter it altogether from attacking. Clearly, then, to maintain military deterrence, a nation would have to be believed to have retaliatory power so great that a potential aggressor nation would have reason to think that it could not defend itself against such retaliation.
If the statements above are true, which one of the following can be properly inferred?
A. A would-be aggressor nation can be deterred from attacking only if it has certain knowledge that it would be destroyed in retaliation by the country it attacks
B. A nation will not attack another nation if it believes that its own retaliatory power surpasses that of the other nation.
C. One nation's failing to attack another establishes that the nation that fails to attack believes that it could not withstand a retaliatory attack from the other nation.
D. It is in the interests of a nation that seeks deterrence and has unsurpassed military power to let potential aggressors against it become aware of its power of retaliatory attack.
E. Maintaining maximum deterrence from aggression by other nations requires that a nation maintain a retaliatory force greater than that of any other nation.
解析： 文章内容：（1）军事威慑与怕报复之间的关系；（2）国家要有足够报复能力让潜在的入侵国相信打不过它。
A项：出现了only，表示此项不能选，因为原文中没有绝对化词汇出现。文章是说有报复能力会让潜在入侵国不敢动手，但也可能有其他原因让潜在入侵国不敢动手，比如某国受第三国保护，虽然某国没有足够报复能力，但潜在入侵国也不敢动手。
B项：报复力更强。文章中只说会避免被其他国家侵犯，没有说报复力更强的国家是否会入侵别国，不可选此项。
C项：此项和A项描述的事件类似。但是别国不入侵，完全可以是因为其他理由，并不只是因为此国的报复能力，比如这两个国家自古以来关系甚佳。
D项：“符合国家利益的是国家要有强的军事力量让潜在入侵者意识到它的报复能力。”有同学可能会说“符合国家利益”这些词原文中找不到。这种想法完全不正确。逻辑题不要求选项词汇和文章词汇一一对应。比如选项用一个词能概括原文中的两句话，这个词虽然没有明确说出来，但通过逻辑是可以接受的，则被认为是正确的。因此，我们做题时，不能追求任何的形式，比如只看选项的词是否和原文一样，而是要通过逻辑去思考。“让国家不被入侵”这件事情当然可以被认为是“符合国家利益”的，故此项任何一处都不能说是错误的，放着此项待选。
E项：出现两个最高级，肯定不正确，排除此项。
答案为D项。
例2 People with a certain eye disorder are virtually unable to see in moderately bright light, which seems to them unbearably intense, since the cells of their retinas are overwhelmed by moderately bright light. These people do, however, show normal sensitivity to most components of dim light. Their retinal cells are also not excessively sensitive to red components of moderately bright light.
The information above best supports which of the following hypotheses about people with the disorder described, if they have no other serious visual problems?
A. In all moderately dim light in which people without the disorder can read large print, people with the disorder cannot read such print.
B. In an otherwise darkened concert hall, these people will see a dimly illuminated red exit sign more clearly than small dim white lights that mark the aisles.
C. These people typically see more acutely at night and in dim light than do most people who do not have the disorder.
D. Eyeglasses that are transparent to red components of light but filter out other components of light help these people see in moderately bright light.
E. These people perceive colors other than red in the same way as do most people who do not have the disorder.
解析： “hypotheses about people with disorder”表明选项和原文是一个方向即可成为备选答案，不要因为某选项出现新词汇而排除这个选项。
原文描述三件事：（1）有眼病的人正常亮度下看不清；（2）暗的光线里面可看见；（3）正常亮度里看得见红色光线。
在做所有的GRE逻辑题过程中，事件描述的范围一定要多加关注，比如这道题中的范围有正常亮度和暗的光线。
A项：原文中讲有眼病的人在光线暗的环境中看得见，所以此项和原文内容冲突。
B项：在暗光线里面可看得见，在正常亮度下有眼病的人看得见红色光线，但在暗光线下有眼病的人对红色光线会有什么样的反应，文章没有告诉我们，所以排除此项。
C项：暗光线中，有眼病的人看得见。从原文得不出这些人比正常人能够看得更清楚。
D项：“过滤掉红色光线之外的其他光线的眼镜可让有眼病的人在正常亮度中看得见。”这项和原文描述的事件三是一个方向，可放着待选。不可因为eyeglass在文章中没有出现过而直接排除此项。
E项：从原文中我们只知道看得见红色光线，接收红色光线的方式我们不清楚，所以E项不能选。
D为答案。
例3 In Patton City, days are categorized as having heavy rainfall（more than two inches）, moderate rainfall（more than one inch, but no more than two inches）, light rainfall（at least a trace, but no more than one inch）, or no rainfall. In 1990, there were fewer days with light rainfall than in 1910 and fewer with moderate rainfall, yet total rainfall for the year was 20 percent higher in 1990 than in 1910.
If the statements above are true, then it is also possible that in Patton City
A. the number of days with heavy rainfall was lower in 1990 than in 1910.
B. the number of days with some rainfall, but no more than two inches, was the same in 1990 as in 1910.
C. the number of days with some rainfall, but no more than two inches, was higher in 1990 than in 1910.
D. the total number of inches of rain that fell on days with moderate rainfall in 1990 was more than twice what it had been in 1910.
E. the average amount of rainfall per month was lower in 1990 than in 1910.
解析： 原文里面说了三件事情：（1）天气可以被归类为四类（没有雨；降雨量小于1英寸；降雨量1~2英寸；降雨量2英寸以上）。（2）1990年下小雨和中雨的天数少。（3）1990年的降雨总量更多。
请问考生“通过1990年下小雨和中雨的天数少，以及1990年的降雨量多，可否推出1990年降大雨的天数更多”？答案是不一定。导致1990年总降雨量更多有其他理由，比如1990年下大雨的天数和1910年一样多，但是因为大雨是降雨量2英寸以上，文章中并没有说明最高值是多少，所以1990年的大雨可以降10英寸，而1910年只有3英寸，这样也会导致1990年的总降雨量更多。即1990年降大雨天数可以少于1910年，只要1990年的单次降雨量更大即可。
此题问哪个选项可能对，表示只要和文章不冲突的选项即可成为答案。因此，五个选项一定是由四个和文章冲突的选项和一个推出或推不出但和原文不矛盾的选项组成。
A项：正如上文所分析的，1990年可能大雨的降雨天数更少，但只要降雨量大到一定值，即可导致1990年总降雨量大于1910年的。
B和C选项：1990年下雨但不超过2英寸，那只有下小雨和中雨。文中倒数第二行明确地说明是“fewer days”，所以B和C两项全错。
D项：假设1990年和1910年的下中雨天数一致，中雨降雨量是开区间1~2英寸，那么即使两年的下中雨天数一样，也不会得出某年降雨量是另一年降雨量的两倍这一结论，更何况文章告诉我们1990年下中雨的天数更少，所以D项也和原文冲突。
E项：平均月降雨量是年降雨量除以12后得到的，所以年降雨量更高的1990年不可能月平均降雨量更低，E项也和原文冲突。
此题答案选A。
从归纳题的内容来看，有些归纳题带有数学概念。比如原文中告诉我们某辆车的时速以及行驶时间，则行驶距离是可计算的，这时如果在选项中出现“距离”不能认为是原文没有提及而被当作新概念。可以通过常识（包括数学知识）推测出来的内容都不算新概念。
例4 Fact: Asthma, a bronchial condition, is much less common ailment than hay fever, an allergic inflammation of the nasal passages.
Fact: Over 95 percent of people who have asthma also suffer from hay fever.
If the information given as facts above is true, which of the following must also be true?
A. Hay fever is a prerequisite for the development of asthma.
B. Asthma is a prerequisite for the development of hay fever.
C. Those who have neither hay fever nor asthma comprise less than 5 percent of the total population.
D. The number of people who have both of these ailments is greater than the number of people who have only one of them.
E. The percentage of people suffering from hay fever who also have asthma is lower than 95 percent.
解析： 原文可用表示集合的韦恩图表示：大圈是hay fever，小圈是ashma。95% ashma是两者交集。
从原文中并不能得知两种疾病谁先谁后发生，因此A和B项中含有prerequisite，都是错误的。
C项：“没有得病的人数是5%”，此项在问上述两个圈之外的空间是多大，外框多大，我们无法得知，故此项不正确。
D项：“两项之间的交集比任何一项都大”，如上图所画，交集不可能比“hay fever”这一元素更大，此项不正确。
E项：我们得知hay fever的总量比asthma大，二者的交集占了asthma 的95%，那么相同大小的交集占hay fever的比例肯定低于95%，所以E项正确。
例5 From 1980 to 1989, total consumption of fish in the country of Jurania increased by 4.5 percent, and total consumption of poultry products there increased by 9.0 percent. During the same period, the population of Jurania increased by 6 percent, in part due to immigration to Jurania from other countries in the region.
If the statements above are true, which of the following must also be true on the basis of them?
A. During the 1980's in Jurania, profits of wholesale distributors of poultry products increased at a greater rate than did profits of wholesale distributors of fish.
B. For people who immigrated to Jurania during the 1980's, fish was less likely to be a major part of their diet than was poultry.
C. In 1989 Juranians consumed twice as much poultry as fish.
D. For a significant proportion of Jurania's population, both fish and poultry products were a regular part of their diet during the 1980's.
E. Per capita consumption of fish in Jurania was lower in 1989 than in 1980.
解析： 文章描述四件事情：（1）鱼的消耗增加4.5%。（2）家禽的消耗增加9%。（3）人口增加6%。（4）人口多部分是因为移民的到来。
A选项：从文中四件事情中，不可能推出利润多少，所以排除本项。
B选项：“鱼可能成为主食的可能性较小”，在原文中我们只知道鱼和家禽的消耗增加了。人们是把鱼当主食吃还是当零食吃？是偶尔吃还是经常吃？偶尔吃的东西会成为主食，还是经常吃的东西会成为主食？皆有可能。所以B项的“major part of the diet”不可被确定地推出来，排除此项。
C选项：文章中描述的是百分比，属于相对值。此项描述的是绝对值，如果此项正确那只得假设鱼和家禽的基值一样，但文章中没有告诉我们基值的信息，所以排除此项。
D选项：排除此项的理由和B项类似。
E选项：“人均鱼肉消耗量在1989年更低”。1989年鱼的人均消耗量= [1980年鱼的消耗量×（1+4.5%）]÷[1980年人口数（1+×6%）]
分母比分子变化更大，所以E项为答案。
例6 The total market value of real estate in Altonville has steadily declined over the past four years. This decline has meant that the overall figure on which the city's property tax is based—the assessed value of that real estate—has also declined. Moreover, the percentage of assessed value that was paid as property taxes to the city did not change during this period.
The information above most strongly supports which of the following?
A. Money collected from property taxes provided most of Altonville's revenue during the past four years.
B. The percentage of Altonville's overall revenue that was collected from property taxes did not change over the past four years.
C. Altonville officials had proposed raising property tax rates during the past four years but never did so because of strong opposition from property owners.
D. The total amount of revenue that Altonville has collected from property taxes has declined over the past four years.
E. During the past four years, Altonville officials also did not increase tax rates on other sources of revenue such as retail sales or business profits.
解析： 文章讲两件事情：（1）房地产估值小了。（2）房产税率不变。
通过这两件事情，自然可推理出交的房产税额（房地产估值×房产税率）变小了。
A项：“房产税贡献了A城市大部分收入”，在原文中我们只能得知房产税会给A城市提供收入，但所提供的收入是否占大多数无法得知，此项排除。如果此项把most改为part，则A项没有出错的地方。
B项：“房产税占总收入的比例没变”，此比例是“房产税÷A城市总的收入”，但A城市的总收入为多少我们无法得知。虽然房产税变少了，但其他的税收可能变多、变少或持平。所以排除此项。
C项：从原文中根本不可能得知官方做了什么事情，排除此项。
D项：“房产税税额少了”，正确。解归纳题时，在总结完所有事件后，可先想想这些事件可以让我们推理出什么，答案并不一定和自己推出的内容一致，但建议考生做下推理，因为这样会增加对正确答案的敏感度。
E项：排除该项的理由和C项一致，官方会做什么事情我们无法得知。
答案为D。
补充知识：对程度词的理解
在GRE逻辑考试中，对程度词掌握不佳会大大影响逻辑推理的正确性。most、majority、some、certain、many、a few、nearly all等程度词内容上有何不同？
1. some=a few = certain = many，都表示超过零个，但不表示超过50%的量。
2. majority =most = nearly all，都表示超过50%的量。
例如：
句1：Some students get GRE 338. Some students go to Harvard.
句2：A few students get GRE 338. Many of them go to Harvard.
句3：Most students get GRE 338. A majority of them go to Harvard.
这三件事情表达的意思有何区别？哪件事情表达了GRE得338分即可进入哈佛大学？
首先，三件事情都不能表达GRE考338分即可进哈佛大学，因为most表示“最多”，超过50%。
其次，some表示“一部分，一些”，句1的两件事之间不一定产生交集。句1和句2并不能推出有些学生GRE考338分，且去了哈佛大学，因为a few和many都表示“一些”的意思。
most和majority表示超过50%，所以句3可表示有些学生GRE考338分，其中有些学生考入哈佛大学。