以下摘自某权威读物的逻辑讲解以以英文形式展示，大家如果有充足的时间可以阅读一下。内容并不针对考试，大家可以拓展一下对逻辑的了解。
A. Unjustified Assumptions
the most common logical mistake on the GMAT, occurring in more than half of all arguments.
this sort of flaw requires an unspoken and unsupported premise—that is, the author is depending on a premise that he or she didn’t write down and hasn’t proven. Thus, the conclusion
can’t be validated unless the assumption can be proven.
1. Assumes Shared Beliefs
arguer assumes that the listener will share certain basic beliefs—some of which are mere impressions, prejudices, and so on.
TIP: Don’t take anything for granted, and don’t bring in outside ideas
2. Draws Extreme Conclusion
The 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. Look for dramatic predictions and assertions: X costs fa r more than Y, an immediate increase in Z, a sharp decline in W.
TIP: Keep in mind that even a perfectly reasonable argument can be destroyed by too strong a conclusion.
3. Assumes Skill and/or Will (HELR方案类)
For people to do something, they have to be able to do it, and they have to want to. Both skill and will are necessary.
4. Uses Vague or Altered Terms
Question any term that’s insufficiently precise.
(FOR INSTANCE:Exercise the same amount is overly vague. Use more)
TIP: any change in terms through the course of the argument should make you arch an eyebrow.
5. Assumes Signs o f a Thing = Thing Itself(有 不等于 成功实施，不等于准确)
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.
a regulation exists doesn’t mean that it is being followed.
TIP: Don’t confuse external signs and reality. Quite often, the signs can be misleading.
B. Causation Errors
Causation errors are prevalent on the GMAT. They can be seen as a species of Unjustified Assumption, but they’re so important that they deserve their own heading.
Many 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. Also look at infinitives {to reduce), which often indicate goals. The achievement of goals requires causation.
6. Mixes Up Correlation and Causation(HELR相关因果的CQ)
To review: If X and Y seem to be correlated, 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.
These four options are the only possibilities. Memorize them! 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.(类似果因排除他因)
Correlation/Causation errors often have to do with changes or events that occur at the same time or in sequence.
TIP: Don’t assume that simultaneous events are necessarily connected. Likewise, if X happened shortly after Y, you cannot necessarily conclude that X was caused by Y.
7. Assumes the Future = the Past
“past performance is no guarantee of future results.”
TIP: the future might be different
8. Assumes the Best Means Success
This flaw could also be called “Just because a plan didn’t work doesn’t mean it wasn’t our best shot,” or“Just because a protection fails doesn’t mean it wasn’t protecting.”
Sometimes even the best thing fails.
BEST是比较出来的，不是自身成功的可能性
C. Comparison Errors
Comparison errors often represent a form of Unjustified Assumption, the assumption typically being that the two things are similar enough in the important ways to be compared.
These errors are so important and so tricky, though, that they get their own section.
9. Has Selection Bias
Whenever 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 when the two groups seem comparable—for instance, when they are both drawn from the same population.
1) Unrepresentative Sample(Helr统计枚举样本的代表性)
You have to ensure that the sample is representative
2) Survivor Bias
It is not logical to judge an entire group by concentrating only on who or what survived a process or time period, while ignoring the non-survivors. Its easy to fall into this trap, though; after all, its often hard to find out much about the people or things that didn’t make it!
Survivor bias can also involve nonliving things。
3) Ever-Changing Pool
随着时间变化，调查对象在一定区域内可能已经发生了变化，即不要假定是固定人群。
10. The Troubled Analogy(HELR 类比)
It’s your job to note the possible dissimilarities.
D. Math Errors (Helr演绎推理)
just be comparing one ratio to another. you’ll have to find mathematically provable conclusions. Notice that this conclusion is based only on inequalities and ratios. This is the way that the GMAT can avoid putting real numbers into arguments and yet still have a rigorous, airtight conclusion.
11. Confuses the Quantities (percents, rates, ratios)
Mathematical flaws in Critical Reasoning arguments usually rely on conceptual confusion.
TIP: you will need to keep percents and real numbers straight.
Don’t confuse percents with actual numbers of dollars, people.
A few other standard mathematical relationships show up in Critical Reasoning as well:
Rate x Time = Distance
Profit = Revenue - Costs
(Dollars per Hour) x Hours = Dollars
E. Communication Errors
12. Missing the Point
When two people argue with one another on the GMAT, one of them often misses the point
This type of flaw is very common when people argue over causes they feel deep emotions about.
IN SUM
The more modest the conclusion, the easier it is for the premises to support that conclusion—and thus,the stronger the argument.In conclusion, watch out for extreme wording or new ideas! Altered terms or standard can seriously weaken an argument.
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