编辑推荐您关注：
LSAT作题及训练方法总结 需专业背景知识原则
逻辑推理题都是基于一个段落(或图表)，所涉及的内容像新闻记者理解的文章一样，涉及研究生在学术研究、日常研读或日常生活中阅读的材料，这些材料可以涉及任何主题---艺术、社会学、历史、哲学、政府、体育、广告等等。虽然涉及内容包罗万象，读懂文章、回答问题，无需任何学科、专业的特定知识，并且不能借助自己熟悉的专业知识来考察，而应着重从逻辑推理的角度来思维。尽管逻辑应用与技法类型的考题有些涉及逻辑学的部分专用术语，但并不需专门的逻辑学专业的知识，否则将违反ETS许诺的公平性原则：对任何一个考生都是公平的。当然，作为一名大学生，一些 common sense必不可少，如供求规律、数学里的比例、交集等。我的建议是：不要因你所读到的问题的主题是你不熟悉的而感到畏惧。即使主题是你从未读到的或听到的，你回答问题所需的一切信息均已包容在段落之中。
Which of the following 原则
逻辑推理题的大多数问题有which of the following，要求你根据段落里所给信息及逻辑推理，从下面五个选项中选出一个选项，从而实现问题目的。有时，或许这个选项并不是专业知识背景下或常识中的最佳选项，但只要是五个选项中最能实现问题目的的选项就可以了。逻辑推理题中一般不会出现两个或两个以上选项同时实现问题目的，让考生挑选一个最好的选项。实际上，在问题目的中的most在绝大多数情况下无意义，也就是说，五个选项中，只有一个对，其他四个必然不对。不过，在有些情况下，问题目的中的best有意义。请认真体会以下两个例子：
The skulls and pelvic bones of some species of dinosaur share characteristics with the skulls and pelvic bones of all modern birds. Even though not all dinosaurs have these characteristics, there are scientists who claim that all animals that do have these characteristics are dinosaurs.
If the statements above and the claim of the scientists are true, which of the following must also be true?
(A) Birds share more characteristics with dinosaurs than they do with other animals.
(B) Some ancient dinosaurs were indistinguishable from modern birds.
(C) All animals whose skulls share the characteristics of those of modern birds also have pelvic bones that are similar to those of modern birds.
(D) Modern birds are dinosaurs.
(F) All dinosaurs are birds.
译文：一些恐龙的头盖骨和骨盆骨与所有现代鸟类的头盖骨和骨盆骨有许多相同特征。虽然不是所有的恐龙都有这些特征，但一些科学家声称，所有具有这些特征的动物都是恐龙。
如果上面的陈述和科学家的声明都是正确的，下列哪一项也一定正确?
(A) 鸟类与恐龙的相似之处要多于鸟类与其它动物的相似之处。
(B) 一些古代恐龙与现代鸟类是没有区别的。
(C) 所有动物，如果它们的头盖骨和现代鸟类的头盖骨具有相同特征，那么它们的骨盆骨也一定和现代鸟类的骨盆骨具有相同特征。
(D) 现代鸟类是恐龙。
解析：科学家根据陈述：“一些恐龙的头盖骨和骨盆骨与所有现代鸟类的头盖骨和骨盆骨有许多相同特征”，就得出结论：“所有具有这些特征的动物都是恐龙”。根据逻辑推理，我们发现(D)正确。显然，若根据常识，(D)必错无疑，但就逻辑推理而言，归纳的段落所面临的推理是必定成立的推理，所以(D)可从上面段落中推出来且与上面段落吻合，所以(D)正确。(A)做了一个无关比较，无关比较必然不对，且“the animals”是新概念;(B)中的“indistinguishable”不可能从上面段落中得到;(C)中的“all animals”把讨论范围扩大，犯了递推的错误;(E)是的all明显也是把段落中的“some”范围扩大化，因此也必然不对。
The ice on the front windshield of the car had formed when moisture condensed during the night. The ice melted quickly after the car was warmed up the next morning because the defrosting vent, which blows only on the front windshield, was turned on full force.
Which of the following, if true, most seriously jeopardizes the validity of the explanation for the speed with which the ice melted?
(A) The side windows had no ice condensation on them.
(B) Even though no attempt was made to defrost the back window, the ice there melted at the same rate as did the ice on the front windshield.
(C) The speed at which ice on a window melts increases as the temperature of the air blown on the window increases.
(D) The warm air from the defrosting vent for the front windshield cools rapidly as it dissipates throughout the rest of the car.
(E) The defrosting vent operates efficiently even when the heater, which blows warm air toward the feet or faces of the driver and passengers, is on.
译文：水汽会在夜晚凝结，在汽车的前挡风玻璃上形成冰。第二天早上汽车逐渐发动起来以后，因为除霜口调到最大，而除霜口吹向前挡风玻璃，因此(在前挡风玻璃上的)冰很快就融化了。
以下哪一选项，如果是正确的，最严重地威胁到这种关于冰融化速度的解释?
(A)两边的玻璃没有冰凝结在上面。
(B)尽管没有采取任何措施对后窗进行解冻，但那儿的冰同前挡风玻璃上的冰的融化速度一样快。
(C)从除霜口吹向前挡风玻璃的热空气，当它扩散到汽车内其他部分时迅速地冷却。
(D)即使当把热空气吹向司机和乘客的脚和脸部的暖气打开时，除霜口仍可以很有效率地工作。
解析：挡风玻璃上的冰融化的速度取决于从除霜口全力吹向前挡风玻璃的空气。如果如(B)所说，没有采取措施对后窗进行解冻，而后窗的冰同前挡风玻璃上的冰融化得一样快，那么就削弱了该解释，因此，(B)是正确答案。在没有其他信息的条件下，(A)中所提到的在边窗上没有冰的凝结同该解释的有效性无关;选项(C)可以支持该解释，因为从解冻风口吹出的空气是热的;(D)和(E)都不能提出一个理由去怀疑是从风口吹出的空气导致了冰的融化，因此都没有威胁到该解释的有效性。从这个例子我们可以看出，五个选项中只有(B)可以实现问题目的，而其他四个选项都不可能实现问题的目的，即只有一个选项是正确的。
if true 原则
if true 在许多考题中出现，紧接在Which of the following 之后，有时表达为if practicable，if accepted，if feasible，if correct，if established等。这使得选项在即使违反常识或专业知识的情况下，我们也不能质疑其正确性。应牢记的是：在五个选项内容本身无可质疑的情况下，通过考察推理能否成立，有无缺陷，去实现问题目的。段落或选项中所表述的信息、观点或事实是否正确并不是我们所关注的问题。
Pandas are rapidly disappearing from the wild. Therefore, in order to preserve the species, existing pandas should be captured and placed in zoos around the world.
Which of the following statements, if true, casts most doubt on the conclusion drawn above?
(A) When in captivity, pandas typically produce more young than they do in their native habitat.
(B) Newborn pandas in zoos are not likely to die from infectious diseases, whereas newborn pandas in the wild are likely to die from these diseases.
(C) Sufficient quantities of bamboo, the panda’s only food, cannot be made available outside the panda’s native habitat.
(D) Many zoos are eager to increase their stock of rare and exotic animals, but there are not enough pandas for all the zoos that want one.
(E) Pandas in zoos have as many offspring that survive to adulthood as do pandas in the wild.
译文：野生大熊猫正在迅速减少。因此，为了保护该物种，应把现存熊猫捕捉起来并放到世界各地的动物园去。
下面哪个，如果正确，对上述结论提出了最严重的质疑?
(A)大熊猫在关起来时通常分比在天生栖身地时生下更多的小熊猫。
(B)在动物园中刚生下来的熊猫不容易死于传染病，但是野生的熊猫很可能死于这类疾病。
(C)在熊猫的栖息地以外，很难弄到足够数量的竹子，这是熊猫惟一的食物。
(D)许多动物园急于增加收藏稀有的珍奇的动物，但是大熊猫的数量不够所有想得到一只的动物园分配。
(E)动物园里的大熊猫和野生的大熊猫后代中能够活到成年的熊猫的数量相当于。
解析：本题推理为达到一个目的而提出一种解决方法，即为了保护熊猫，应把他们放到动物园里。反对大多反对A，即方法A不可行或无意义。(A)、(B)起到支持作用;(D)动物园的希望与为了保护熊猫而提出的方法无关;(E)无关选项，虽然动物园里与野生环境中的熊猫有相同数量的后代，但仅仅由数量并不能说明问题。例如野生环境中有50只熊猫，有10只存活，动物园中有500只熊猫，也有10只存活，虽然存活数量相同，但基数不一样，结论则大相径庭。如果熊猫惟一的食物竹子不能在天然栖息地之外得到，正如(C)所说，那么也就反对了上面所提出的方法：把这些熊猫放到动物园里。但有的读者根据常识认为，大熊猫作为国宝，如果用飞机把熊猫的天然栖息地的竹子运过去就行了，因此(C)不正确。这样是思维所犯的错误就是没有理解“if true 原则”限定了(C)选项的本身意思不能受到质疑。请读者认真体会if true的意思。
五中选二的原则(The rule of 2 out of 5)
逻辑推理题编写的一个基本原则是五个选项中的一个选项必须比其他的四个好。然而，正确选项的设计不能比其他四个选项明显地好以致问题的难度变得太小。这个原则使逻辑推理的命题人员陷入了左右为难的境地。如果一个问题让你去驳斥一个论证，那么一个选项必须能对段落的内在逻辑构成反对。这个选项将是“credited response”。另外四个选项——迷惑选项distractors一定在某些方面不完美，但他们不能不一目了然，使问题变得ridiculously easy。从某种意义上讲，Preparing workable distractors is actually more difficult than writing the credited response。因此，通常五个选项中只有两个选项值得考虑(两者中仅仅在一个是对的)。另外三个选项，尽管有时与推理主题有点关联，但它们都有忽略了论点的推理结构。牢记：Usually only two of the answer choices have any real merit (one being the correct choice).
总之，使得五个选项中只有一个难以排除，其他三个选项在很多情况下可能与问题目的无关，所以怎么样迅速排除三个选项是提高解题速度的关键。我在与ETS负责命题的官员谈话时明显觉察到：编制逻辑推理题的最大痛苦与挑战不在于如何编制出一个非常像正确答案但又绝对不是正确答案的选项。实际上，有时五个选项中四个选项都编得极为荒谬，错得极为明显，只要阅读水平没问题，正确答案便跃然纸上。读者应在本书的大量归类讲解与训练中，培养挑选正确选项的感觉，进而找出错误选项特征。请看下面这个例子：
Over the past fifteen years, the largely urbanized Northeastern United States has shown more and more the influence of the Southwestern portion of the country. Once, very few people in New York City could be found sporting cowboy boots and Stetson hats, and no major radio station boasted twenty-four-hour-a-day programming of country and western music. The latest development is the rapid proliferation of restaurants serving chili, nachos, burritos, and other Tex-Mex dishes.
The passage above makes which of the following assumptions?
(A) The lifestyle of people in the Northeast has been enriched by the influence of the Southwestern states.
(B) Most residents of the Southwestern states regularly eat at Tex-Mex restaurants.
(C) Over the last fifteen years, residents of the Southwestern United States have increasingly adopted lifestyles similar to those of the Northeast.
(D) Tex-Mex dishes are an element of the regional cuisine of the Southwestern states.
(E) People in the Northeastern United States eat out more frequently than they did fifteen years ago.
解析：本题的正确答案是(D)。The author claims that the Northeast has absorbed elements of the culture of the Southwest and provides three examples. A tacit assumption (one which is not Proved) of the argument is that a certain mode of dress, a kind of music, and a type of cuisine are found in the Southwest. (D) articulates this assumption.
Three of the remaining choices are really just “flak.” They lack any6 real plausibility after a reasonably careful reading. These are (A), (C), and (E).
(A) goes beyond the scope of the initial statement. The author simply states that certain cultural elements of the Southwest have been transplanted to the Northeast, but no value judgment is contained in the paragraph about that process.
(C) reverses the causal linkage described by the initial statement. According to the author, the Southwest has influenced the Northeast---not vice versa.
(E) goes beyond the scope of the initial statement. Nothing in the argument suggests that people in the Northeast are eating out more frequently than they did fifteen years ago----only that there more Tex-Mex restaurants in the region than there were fifteen years ago.
对大多数人而言，(B)最易误选。It at least has the merit of being fairly closely connected to the argument in the initial statement. It might be true that people in the Southwest regularly patronize the Tex-Mex restaurants. That, however, is not necessarily an assumption of the argument. All that is required for the argument is that there exist in the Southwest such restaurants---not that residents of that area patronize those restaurants with any frequency.
由上例可以看出，五个选项中的(A)、(C)和(E)的编写都非常荒谬，错得较为明显。“五中选二”的两个选项为(B)、(D)，也就是说这五个选项中只有(B)、(D)值得考虑。(B)易误选。而正确答案只有一个，即(D)。
