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[转帖]Stewart-Unstated Assumptions
http://www.west.net/~stewart/gmat/qa_7.htm
Unstated Assumptions
—The Inner Sanctum of GMAT Critical Reasoning
This Q&A focuses on the three most common types of Critical Reasoning questions. You'll learn how they're related to one another, how the test-makers design these questions, and how you can be ready for them.
Q: What cognitive abilities do Critical Reasoning questions measure, and how do the questions accomplish this?
A: Critical Reasoning questions are designed to gauge your ability to think critically and analytically—more specifically:
• To recognize reasoning errors and unstated assumptions
• To follow an argument’s line of reasoning
• To draw reasonable inferences from stated premises
Each Critical Reasoning question provides a paragraph-length argument, along with a question pertaining to that argument. Each question will require you to perform one of the following seven tasks (I’ll also indicate here how the question itself might be phrased):
1. Recognizing how to undermine (seriously weaken) an argument
("Which of the following, if true, would most seriously weaken the argument above?")
2. Recognizing how to support (strengthen) an argument
("Which of the following, if true, would provide most support for the conclusion of the argument above?")
3. Identifying unstated assumptions
("The foregoing argument depends on which of the following assumptions?")
4. Drawing an inference from a series of stated premises
("If all of the statements above are true, which of the following is most strongly supported by them?")
5. Making valid deductions based on a series of premises and/or a conclusion
("If all of the statements above are true, which of the following must also be true?")
("Which of the following statements must be true in order for the conclusion in the argument above to be inferable?")
6. Recognizing patterns of reasoning
("Which of the following demonstrates a pattern of reasoning most similar to the reasoning contained in the argument above?")
("The flawed reasoning above is most similar to the flaw in which of the following?")
7. Recognizing the main point, or final conclusion, of an argument
("Which of the following best expresses the main point of the passage above?")
I’ve listed the question types here in descending order of frequency with which they appear on the GMAT. Nevertheless, you can expect to encounter at least one of each type among the 14-15 Critical Reasoning questions on your GMAT.
Q: Why is it useful to categorize question types?
A: The best approach to the question often depends on the question type. Thus you should always read the question stem (the question itself, apart from the answer choices) before reading the argument, so that you know how to think about the argument as you read it. On the other hand, you won’t gain any insight by reading the answer choices beforehand; you’ll just be wasting precious time by doing so.
Q: Let’s talk about the question types toward the top of your list, since these are the ones that appear most frequently on the test. What specific approaches are best for handling these questions?
A: Okay, let’s focus on the first three question types, because they call for essentially the same approach. For the record, here are the three question types I’ll be discussing here:
• Unstated-assumption questions
• Undermining-evidence questions
• Supporting-evidence questions
For any of these three question types, believe it or not your task is essentially the same: to recognize a particular unstated assumption—a certain fact or condition not explicitly provided but which must be assumed in order for the argument’s conclusion to be readily inferable.
To help you appreciate how similar your approach should be for all three types, let’s follow what should be your basic train-of-thought for each type:
Unstated-assumption question:
As you read the argument ask yourself, "In addition to the stated premises, what must be assumed true here in order for the argument to leap to its conclusion?" Then look for that missing link among the answer choices; that choice will be the best one.
Undermining-evidence question:
As you read the argument ask yourself, "In addition to the stated premises, what must be assumed true here in order for the argument to leap to its conclusion?" Then scan the answer choices, looking for one that refutes, contradicts, or rules out that unstated assumption. That choice will be the best response to the question.
Supporting-evidence question:
As you read the argument ask yourself, "In addition to the stated premises, what must be assumed true here in order for the argument to leap to its conclusion?" Then look for the answer choice that provides, or affirms, the missing link; that choice will be the best response to the question.
Q: Can you provide an example of the sorts of unstated assumptions upon which a GMAT argument might depend?
A: Absolutely. Consider the following GMAT-style argument. The argument’s first sentence contains two premises, while the second sentence states the argument’s conclusion:
During the past year nationwide membership in fitness clubs has declined by about fifteen percent, while sales of fast-food products widely known to contribute to health problems have risen by about the same percent. These statistics clearly show that during the past year consumers have become less concerned about their health and level of fitness.
This same argument could be used for any of the three question types. Regardless of the question, your analysis—as you go from the premises to the conclusion—is the same: Ask yourself what the missing link is. Did any assumptions occur to you? If not, let’s do some brainstorming. Doesn’t the argument depend on all of the following assumptions?
• People join fitness clubs because they are concerned about their health.
• Membership in fitness clubs is the only means by which consumers demonstrate their concern for fitness.
• Renewal rates at fitness clubs are not increasing.
• The fitness-club membership decline is not due to factors such as: (1) memberships becoming prohibitively expensive or (2) the discontinuation of operations by a large nationwide fitness-club chain.
Additional unstated assumptions might occur to you as well. You can take any one of these assumptions and draft it as the best answer choice for any of the three question types.
Q: Can you illustrate your final point, by providing a "best response" to each of the three question types, each one based on the same argument?
A: Sure. For each of the three question types, here’s a sample question along with a viable best answer choice:
Unstated Assumption
Question:
The argument above depends on which of the following assumptions about the most recent one-year period?
Best answer choice:
Concern about health is the primary reason that consumers join fitness clubs.
Undermining Evidence
Question:
Which of the following statements about the most recent one-year period, if true, would most seriously weaken the argument above?
Best answer choice:
People join fitness clubs for the primary purpose of socializing with other club members.
Supporting Evidence
Question:
Which of the following statements about the most recent one-year period, if true, provides most support for the conclusion drawn above?
Best answer choice:
Most consumers who join fitness clubs do so for the purpose of maintaining or enhancing their level of health and fitness.
You could take any one of the assumptions I listed earlier, and draft your own "best response" to each of the three questions. In fact, I recommend this exercise to help you understand how the test-makers think as they dream up Critical Reasoning questions—and answer choices. Getting into the mind of the test-maker is a great way to sharpen your instincts for the GMAT.
Q: Do you have any general brainstorming suggestion for thinking of unstated assumptions as you read an argument?
A: Yes; in a question of any of the three types we’re discussing here, look for either of the following two general assumptions:
1. The assumption that all other factors are equal—if the argument seeks to explain certain Differences between two phenomena
2. The assumption that all other relevant conditions remain unchanged over time—if the argument seeks to explain some sort of change from one point in time to another
My health-and-fitness argument relies on the latter assumption. Other conditions that might be relevant to the argument and that might have changed during the past year include the levels in
• Purchases of fitness equipment for the home
• Consumption of nutritional supplements or health foods
• Interest in preventive health care
The argument can be either weakened or strengthened, depending on whether and of these conditions have changed and, if so, the direction of change.
Q: What about the other responses—the wrong answer choices—To questions of these three types? What are the test-makers’ favorite wrong-answer ploys?
A: In unstated-assumption questions, look out for the answer choice that turns one of the argument’s unstated assumptions on its head. Here are two such answer choices for an unstated assumption question relating to my health-and-fitness argument:
• Concern about health and fitness is not the only reason people join fitness clubs.
• Membership fees at fitness clubs have been increasing overall during the past year.
Similarly, in undermining-evidence and supporting-evidence questions, look out for answer choices that accomplish the opposite of what the question asks. In an undermining-evidence question, that would be a response that actually affirms an unstated assumption; conversely, in a supporting-evidence question, that would be an answer choice that actually contradicts an unstated assumption.
Perhaps you’re wondering why these answer choices wouldn’t jump off the screen at you as obviously wrong. Well, it’s remarkably easy under the pressure of the timed GMAT to inadvertently turn either the argument, the question, or an answer choice, on its head. The best way to avoid falling prey to this ploy is to be aware of it and to read the question stem one more time, along with your selected response, before confirming that response and moving on to the next question.
Q: What other wrong-answer ploys are test-takers likely to encounter when tackling these three types of questions?
A: Regardless of which of the three question types you’re dealing with, most of the remaining wrong-answer choices will simply be irrelevant to the argument. In other words, even if true they accomplish nothing toward either weakening or strengthening the argument. Here are three examples, which could easily be used together as answer choices for any of the three types of questions involving my health-and-fitness argument:
• Last year consumers spent less money on fitness-club memberships than on fast food.
[Irrelevant; the argument seeks to explain changes in two spending patterns, not to compare total spending in one area with total spending in another.]
• The overall level of health and fitness among consumers declined last year.
[Irrelevant; the argument’s conclusion involves a trend in concern among consumers about health and fitness, not in their actual health and fitness.]
• Consumers having a low level of health and fitness tend to spend more money on fast food than other consumers do.
[Irrelevant; the argument’s conclusion involves a trend in concern among consumers about health and fitness, not in their actual health and fitness.]
Q: Can you recommend a step-by-step methodology for handling any question of the three types we’ve been discussing?
A: Sure; here’s a 6-step approach for handling any unstated-assumption, undermining-evidence, or supporting-evidence question:
1. Read the question stem (the question itself, but not the answer choices) before you read the argument.
2. As you read the argument, identify the premises and the conclusion. Doing so will help you follow the argument’s line of reasoning. Keep in mind that the conclusion will not always appear last. In my health-and-fitness example, I could just as easily have stated the conclusion before the premises:
During the past year consumers have clearly become less concerned about their health and level of fitness. After all, during the past year nationwide membership in fitness clubs has declined by about fifteen percent, while sales of fast-food products widely known to contribute to health problems, have risen by about the same percent.
3. Ask yourself: What relevant conditions must be assumed equal, or unchanged over time, in order for the conclusion to be strongly inferable from the premises? Try to formulate at least one or two assumptions—but don’t dwell on it too long. If nothing occurs to you after a few seconds, go on to step 4.
4. Scan the answer choices for one that reflects any of the unstated assumptions that have already occurred to you. Chances are you’ll find one of them among the five choices.
5. If your predetermined assumption is not among the answer choices, then consider each answer choice more carefully, in turn. Having taken a highly active approach to the question, you’re far more likely to recognize the best response when you see it.
6. If you’re unable to determine the best response, look for answer choices that accomplish the opposite of what the question asks for, and answer choices that are irrelevant to the argument. Eliminate them in order to increase your odds of responding correctly to the question.
Q: What’s the best way to prepare for the Critical Reasoning portion of the GMAT?
A: Perhaps more so than for any other question type on the GMAT, preparing for Critical Reasoning questions should involve developing skills—rather than rote practice. Accordingly, if you’re still in college, or even in a graduate program, consider enrolling in an introductory course in critical thinking. These courses might be offered through the school’s Philosophy or Communications department, or both.
If you’re out of school, you might consider enrolling in an evening or weekend course, if you have enough time before the GMAT. Otherwise, obtain at least one or two GMAT-prep books that contain extensive lesson materials for Critical Reasoning, as well as detailed explanations for practice questions. detailed explanations are important, because they can reveal errant patterns in your thinking that you need to correct in order to improve your GMAT Critical Reasoning performance. |
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