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# Good CR notes i came across...hope they will be useful to my

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Good CR notes i came across...hope they will be useful to my fellow GMAT takers

CRITICAL REASONING NOTES

This chapter is divided into two parts:
I. Six Principles for Critical Reasoning Questions
II. The Seven Main Types of Critical Reasoning Questions
I. Six Principles for Critical Reasoning Questions
Critical Reasoning questions typically involve an argument. To address Critical Reasoning questions, you must learn how to analyze logical arguments.
A. Learn how to identify arguments
B. Types of arguments
C. Putting it into your own words
D. Evaluate an argument
E. Evaluate an argument's strength and validity
F. Get an idea of the right answer
G. Don't fall for traps from test writers

II. Typical Critical Reasoning Question Types
A. Must Be True Questions
B. Assumption Questions
C. Strengthen and Weaken Questions
D. Main Point Questions

A. Learn how to identify arguments
Is the text an argument? An argument here doesn't mean a dispute or controversy. It means an attempt to provide a reason for believing something by citing something else. It is an attempt to show that something is true, or probably true, by appealing to something else, some reason or evidence, which indicates that it is true.
The following text includes an argument:
New evidence shows that the AIDS virus may not be as lethal as it has been thought to be and that some people may be able to develop a defense against it. The evidence involves an appreciable number of people who have been HIV positive for many years (some of them for twelve years or more). Lab tests show that the virus is present in their blood. But they have not developed any symptoms of AIDS. They continue to be in good health and show no signs of developing the disease. Some researchers estimate that as many as 5% of those infected by the virus may be in this category and that they will never develop the disease.
In this text a claim is made about how lethal the AIDS virus is. It may not be 100% lethal. Some people may be able to resist it, perhaps because of a natural immunity. And some evidence is cited to show that this claim is true. That evidence is the (alleged) fact that some people have had the AIDS virus in their system for many years and show no signs at all of developing the disease. It is plausible to think that the person who wrote that text intended to cite that fact as a reason for believing the claim about the lethality of the AIDS virus.

Premises and Conclusions
In an argument some claims are put forward in support of others. The claim that is being supported is the conclusion. The claims which are alleged to support the conclusion are the premises. There may be more than one conclusion in an argument, and often, there is more than one premise. In the argument above about AIDS, there is a closely related set of conclusions.
New evidence shows that the AIDS virus may not be as lethal as it has been thought to be and that some people may be able to develop a defense against it.
In support of these conclusions, the author cites the (alleged) fact that some people have been infected with the virus for a long time without showing any signs of the disease itself. This latter assertion is the premise in this argument.
How do you identify premises and conclusions? Reliable clues are provided by certain key words, which are often used to identify premises and conclusions. The following words and phrases are quite often used to introduce conclusions:
So...
This shows that...
Therefore...
We can infer that...
Hence...
Consequently...
It follows that...
This indicates that...
For that reason, we may say...
These are phrases that introduce the premises of an argument:
The reason is that...
Because...
Since...
Evidence...
On the basis of...
It follows from...
In view of...
We may infer from...
When you are able to identify premises and conclusions, you may easily analyze how strongly the premises back up the conclusion. In many of the Critical Reasoning questions, there will be a gap between the premises and the conclusion--the assumptions. Your objective is to find the gaps (the assumptions) and use that knowledge to find the solution. For example, in the AIDS argument above, one of the unstated assumptions is that the evidence about AIDS is accurate.
Premises + Assumptions = Conclusion
B. Types of arguments

B. Types of Arguments (If you have limited time to prepare, skip to C.)
Now that you can identify premises and conclusions, how are they structured into arguments?

Deductive and Inductive Arguments
Deductive arguments are arguments that show a tight connection between the premises and the conclusions. There is no possible way the conclusion could fail to be true if the premises are true. (That is not to say, of course, that the premises are true.) Arguments in mathematics and in pure logic are often of this sort: "If no one watered my plants during my vacation, they will all die. No one watered my plants during my vacation. Therefore, my plants have all died." The premises of that argument might possibly be false. But, if they are both true, then there is no way the conclusion can be false.
There are other arguments with a looser connection. If the premises are true, then the conclusion is likely to be true also; it would be surprising if the conclusion were false; we have good reason to think that the conclusion is true, and so on. These are the inductive arguments. The AIDS argument above is inductive. The conclusion of the argument is that it seems probable that in some way the disease has been successfully stalled.
In both sorts of arguments, the premises support the conclusion if those premises are true. But if they are false, they provide no such support. Discovering that a premise is false, then, undercuts the force of both deductive and inductive arguments.
Because inductive arguments are not conclusive, they may be weakened (perhaps rejected entirely) even if we continue to recognize that their premises are perfectly true. If, for example, researchers were to identify a virus very similar to the AIDS virus, and if they discovered that the incubation period for this virus in chimpanzees often exceeded fifteen years, that discovery would seriously weaken the argument in the example. But it would not show that any of the premises of the original argument were false. It would not show that some people have not survived, and in good health, for twelve years after having been infected. It weakens the argument by introducing another possibility, that the AIDS virus may have a longer incubation period than previously thought plausible.
Inductive arguments can also be strengthened by the introduction of new data. If it were discovered that there is a similar virus which infects chimpanzees, and for which many chimpanzees develop a resistance which enables them to live out a normal life span in good health, that would further bolster the conclusion that perhaps some humans can make a similar defense against AIDS.
C. Putting it into your own words

C. Putting it into your own words

Now that you know how to break down arguments into premises and conclusions, you are able to translate a passage into your own words.

Each question is divided into two parts: the stimulus (the first part of the question that usually consists of an argument) and the stem, which asks a questions such as, "which of the following is an assumption of the paragraph above?" When you finish reading the stimulus, try to summarize in your mind what the argument in the stimulus is about (premises, conclusions, and assumptions). Most of the stimulus parts of the questions have a flaw that you can readily identify, such as a flawed assumption. When you put the argument in your own words, you can usually identify what the stem will ask before you even get to it. This process helps you identify the meaning of the stimulus. Usually the stimulus describes something very simple in a complicated manner, and putting it in your own words helps you to get a handle on what the passage means.
Apartment building owners argue that rent control should be abolished. Although they acknowledge that they would increase rents in the short term, owners argue that in the long term the rent increases would lead to greater profitability. Higher profits would lead to increased apartment construction. Increased apartment construction would then lead to a greater supply of residences and lower prices as the potential apartment residents have a better selection. Thus, abolishing rent control would ultimately reduce prices.
Try to express that complicated argument in your own words? Simple. Abolishing rent control will increase the supply of housing (premise); greater supply leads to lower prices (premise); and thus abolishing rent control leads to lower rents (conclusion). It is a supply/demand argument.
Once you put it into your own terms, the question becomes much easier to understand.
D. Evaluate an argument

D. Evaluate an argument
Now that you can break a stimulus into premises and conclusions and put the argument into your own words, how do you find errors in the arguments?
The Usual Suspects: Common Logical Fallacies
We've identified several logical errors that commonly appear in the Critical Reasoning questions.
1. Circular Reasoning
Here, an unsubstantiated assertion is used to justify another unsubstantiated assertion, which is, or at least could be, used to justify the first statement. For instance, Joe and Fred show up at an exclusive club. When asked if they are members, Joe says "I'll vouch for Fred." When Joe is asked for evidence that he's a member, Fred says, "I'll vouch for him."

2. The Biased Sample Fallacy

The Fallacy of the Biased Sample is committed whenever the data for a statistical inference is drawn from a sample that is not representative of the population under consideration. The data drawn and used to make a generalization is drawn from a group that does not represent the whole.
Here is an argument that commits the fallacy of the biased sample:
ln a recent survey conducted by Wall Street Weekly of its readers, 80% of the respondents indicated their strong disapproval of increased capital gains taxes. This survey clearly shows that increased capital gains taxes will meet with strong opposition from the electorate.
The data for the inference in this argument is drawn from a sample that is not representative of the entire electorate. Since the survey was conducted of people who invest, not all members of the electorate have an equal chance of being included in the sample. Moreover, persons who read about investing are more likely to have an opinion on the topic of taxes on investment different from the population at large.

3. The Insufficient Sample Fallacy
The Fallacy of the Insufficient Sample is committed whenever an inadequate sample is used to justify the conclusion drawn.

Here's an argument that commits the fallacy of the insufficient sample:
I have worked with three people from New York City and found them to be obnoxious, pushy and rude. It is obvious that people from New York City have a bad attitude.
The data for the inference in this argument is insufficient to support the conclusion. Three observations of people are not sufficient to support a conclusion about 10 million.

One of the most often employed fallacies, ad hominen means "to the man" and indicates an attack that is made upon a person rather than upon the statements that person has made. An example is "Don't listen to my opponent; he's a homosexual."
5. The Fallacy of Faulty Analogy
Reasoning by analogy functions by comparing two similar things. Because they are alike in various ways, the fallacy is that it is likely they will share another trait as well. Faulty Analogy arguments draw similarities between the things compared that are not relevant to the characteristic being inferred in the conclusion.
Here's an example of a Faulty Analogy fallacy:
Ted and Jim excel at both football and basketball. Since Ted is also a track star, it is likely that Jim also excels at track.
In this example, numerous similarities between Ted and Jim are taken as the basis for the inference that they share additional traits.
6. Straw Man
Here the speaker attributes an argument to an opponent that does not represent the opponent's true position. For instance, a political candidate might charge that his opponent "wants to let all prisoners go free," when in fact his opponent simply favors a highly limited furlough system. The person is portrayed as someone that he is not.
7. The "After This, Therefore, Because of This" Fallacy (Post hoc ergo propter hoc)
This is a "false cause" fallacy in which something is associated with something else because of mere proximity of time. One often encounters people assuming that because one thing happened after another, the first caused it, as with "I touched a toad; I have a wart. The toad caused the wart." The error in arguments that commit this fallacy is that their conclusions are causal claims that are not sufficiently substantiated by the evidence.
Here are two examples of the After This, Therefore Because of This Fallacy:
Ten minutes after walking into the auditorium, I began to feel sick to my stomach. There must have been something in the air in that building that caused my nausea.
The stock market declined shortly after the election of the president,thus indicating the lack of confidence the business community has in the new administration.
In the first example, a causal connection is posited between two events simply on the basis of one occurring before the other. Without further evidence to support it, the causal claim based on the correlation is premature.
The second example is typical of modern news reporting. The only evidence offered in this argument to support the claim that the decline in the stock market was caused by the election of the president is the fact that election preceded the decline. While it has been a causal factor, to argue that it is the cause without additional information is to commit the After This, Therefore, Because of This Fallacy.

8. The Either or Thinking
This is the so-called black or white fallacy. Essentially, it says "Either you believe what I'm saying, or you must believe exactly the opposite." Here is an example of the black or white fallacy:
Since you don't believe that the earth is teetering on the edge of destruction, you must believe that pollution and other adverse effects that man has on the environment are of no concern whatsoever.
The argument above assumes that there are only two possible alternatives open to us. There is no room for a middle ground.

9. The "All Things are Equal" Fallacy
This fallacy is committed when it is assumed, without justification, that background conditions have remained the same at different times/locations. In most instances, this is an unwarranted assumption for the simple reason that things rarely remain the same over extended periods of time, and things rarely remain the same from place to place.
The last Democrat winner of the New Hampshire primary won the general election. This year, the winner of the New Hampshire primary will win the general election.
The assumption operative in this argument is that nothing has changed since the last primary. No evidence or justification is offered for this assumption.
10. The Fallacy of Equivocation
The Fallacy of Equivocation occurs when a word or phrase that has more than one meaning is employed in different meanings throughout the argument.

"Every society is, of course, repressive to some extent - as Sigmund Freud pointed out, repression is the price we pay for civilization." (John P. Roche- political columnist)
In this example, the word repression is used in two completely different contexts. "Repression" in Freud's mind meant restricting sexual and psychological desires. "Repression" in the second context does not mean repression of individual desires, but government restriction of individual liberties, such as that in a totalitarian state.
11. Non Sequitor
This means "does not follow," which is short for the conclusion does not follow from the premise. To say, "The house is white; therefore, it must be big" is an example of the Non Sequitor fallacy. It may be a big house, but there is no intrinsic connection with its being white.

12. Argument ad populum
A group of kindergartners are studying a frog, trying to determine its sex. "I wonder if it's a boy frog or a girl frog," says one student. "I know how we can tell!" pipes up another. "All right, how?" asks the teacher, resigned to the worst. Beams the child: "We can vote."

This is argumentum ad populum, the belief that truth can be determined by more or less putting it to a vote. Democracy is a very nice thing, but it doesn't determine truth. Polls are good for telling you what people think, not whether those thoughts are correct.

E. Evaluate an argument's strength and validity

E. Evaluate an argument's strength and validity
Now that you may identify arguments and are able to identify logical flaws, you may assess an argument's strength and validity.
More than simply "putting it in your own words," you need to evaluate an argument's persuasiveness. Actively read the stimulus. Always evaluate the argument and check for assumptions as you are reading the passage. Virtually every passage you read has some form of logical flaw. When you read the essay, make sure to be actively seeking those flaws. Read the stimulus with a specific purpose of finding assumptions and errors in logic.
F. Get an idea of the right answer
F. Get an idea of the right answer
If you can identify an argument and assess its strengths, you may come up with a right answer after reading the stem.

Test takers should not be discouraged if they cannot come up with a pre-phrase. Some questions are difficult and an immediate answer will not jump out at you.

Don't fall for traps from test writers
If you have gone as far as to be able to identify and assess an argument, don't fall into a trap when picking an answer.
Test writing is an extremely time-consuming task. One of the most difficult parts of test writing is generating the "junk" wrong answer choices. Test writers have an easy way out. On nearly every question you will see wrong answers that are either the trick opposites or scope traps. These wrong answers do not do much to test ability; they are simply there to fool inexperienced and unskilled test takers. Test writers like to use them because they take a few seconds to write and fool most students, thereby making the question "harder."
On the positive side, a skilled test taker may quickly identify these two trap questions types. Most of the wrong answers in any given Verbal test will be one of the two types of junk answers. If you can identify the junk answer choices, you may thereby eliminate wrong answers and increase your chances of getting the right answer. Below we have several examples.

Trick Opposites

This is an underhanded trick from test writers that does little to improve the quality of the test. This trap involves contradicting the question stem, the end of the question that asks you what to look for. Here are examples:
1. "All of the following may be inferred from the passage EXCEPT," then give a few borderline answers and one answer that absolutely may be inferred from the passage (which someone picks automatically if he forgot the "EXCEPT").
2. Ask for an assumption in an argument, then give an answer choice that is a summary.
3. "Which of the following weakens the argument above," then give an answer choice that obviously strengthens the argument.
These tricks are intended to catch students who rush through questions. However, you may turn this tactic to your advantage if you read the question stems slowly and carefully. Then you may identify the trick opposites, eliminate them as answer choices, and increase the chances of getting the right answers.
The Scope Trap (this section is a repeat from the Reading Comprehension section)

When it comes to determining the scope of a passage, you need to understand what we mean by "scope". Think of scope as a narrowing of the topic. If you've found the main point, you must also identify what is in the range of the argument. Scope is related to more than just the general topic being discussed, it is the narrowing of the topic. Is the article about graduate-school admissions, MBA admissions, or helping international students get into the business school program of their choice? Each step represents a narrowing of the scope.
Scope is one of the most important concepts for doing well on the verbal section, particularly for high scorers. Why? Put yourself in the position of the test question writers. They must write difficult questions. Only one of the five choices is correct; the rest are junk answers. They have to write questions that a certain number of students will get wrong and they have to make up "junk" answers to fool people. The issue of scope solves both problems for test question writers: it allows them to easily generate wrong answers, and it makes the questions harder because scope is a challenging issue. Most critical reasoning or reading comprehension questions have junk answers that are "outside of the question's scope."
Some common examples of scope junk answers are choices that are too narrow, too broad, or literally have nothing to do with the author's points. Also, watch for and eliminate choices that are too extreme to match the argument's scope; they're usually signaled by such words as all, always, never, none, and so on. Choices that are in some way qualified are usually correct for arguments that are moderate in tone and contain such words as usually, sometimes, probably.
all always never only
words that signal answers that are too strong and therefore usually outside the scope of an argument.

Example:
Some scientists believe that carbon dioxide induced global warming may increase the number of hurricanes in the future and their severity.
What if someone inferred from that statement that
All of this season's severe hurricanes were caused by global warming.
That statement would be outside of the scope of the original argument. The inference made is outside the scope of the argument. The argument is not that strong. What about this statement:
Some of this season's storms may have been caused and exacerbated by global warming.
This statement is more measured and is within the scope of the original argument.
• In general, these phrases indicate statements that are outside of the scope of an argument: always, never, none. Usually on the test, arguments aren't that strong, so answers with extreme language are usually outside the scope of the argument.
• These phrases tend to indicate that a phrase is within the scope of an argument: usually, sometimes, probably.
Strategy: If the question asks "which of the following is NOT an assumption of the argument" or "which of the following does NOT describe an argument made in the passage above," the answer will often be the one with extreme language.

Here is a critical reasoning question that illustrates scope.
Apartment building owners argue that rent control should be abolished. Although they acknowledge that they would increase rents in the short term, owners argue that in the long term the rent increases would lead to greater profitability. Higher profits would lead to increased apartment construction. Increased apartment construction would then lead to a greater supply of residences and lower prices as the potential apartment residents have a better selection. Thus, abolishing rent control would ultimately reduce prices.
Name an assumption made by the owners: (hint: this is a difficult question, but you may eliminate 4 of the 5 answers as outside the scope of the argument).

a) Current residents of rent control apartments would be able to find new apartments once their rents increased.
b) The fundamental value of any society is to house its citizens.
c) Only current apartment owners would profit significantly from market deregulation.
d) New apartment construction will generate a great number of jobs.
e) The increase in the number of apartments available would exceed the number of new potential apartment residents.
Which possible answers are outside of the scope? The scope is the argument that deregulation will increase supply and lower prices. "Name an assumption" means find a direct assumption of that supply/demand argument.
a) Current residents of rent control apartments would be able to find new apartments once their rent increased--is this outside of the scope?
Well, this sentence expresses a nice sentiment for the welfare of renters, but it has nothing to do with our argument, which is about a supply/demand dynamic.
b) The fundamental value of any society is to house its citizens. Is this outside of the scope? Again, nice sentiment, but this does not directly tie into the argument.
c) Only current apartment owners would profit significantly from market deregulation. Is this outside of the scope? The profitability of the apartment owners is not directly relevant. Note: of course if the profitability of the apartments increases, it would help increase supply because other companies would be drawn into the market, thus increasing supply. Indeed this looks good and as if it is an assumption, but "Only current apartment owners" is too limiting. How about newer apartment owners? The profits made by "only current owners" is not the issue at hand; it is the prices of apartments. Again, as previously mentioned, answer choices that use words such as "only" tend to be outside the scope of the question. Here "only" is too restrictive and allows you to eliminate this answer choice.
d) New apartment construction will generate a great number of jobs. This is clearly outside of the scope.
e) The increase in the number of apartments available would exceed the number of new potential apartment residents. Aha! This is an argument about supply and demand, and this is an answer about supply and demand. This is clearly within the scope of the argument, and it is the correct answer. If demand rose with new apartment construction, then prices would not decline, invalidating their argument.

Optional Strategy: Some students prefer to read the question stem first and then read the stimulus itself. This lets the user look more specifically for what the question is asking and identify the question type beforehand. You may choose to this strategy. Many test prep companies recommend this approach. Use your own preference.
If you have any questions
you can ask an expert
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Good CR notes i came across...hope they will be useful to my   [#permalink] 08 Dec 2012, 23:30
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# Good CR notes i came across...hope they will be useful to my

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