SDCAR2010【逻辑入门】（十四）Formal Logic (2)

sdcar2010

Unless

The word unless can also create an if-then relationship. But it can bethe most confusing and counterintuitive “logic” word. Consider this example:
Your CR score will not be high unless you study formal logic.

There are two ways to translate this statement into if-then clauses:
1) If your CR score is high, then you have studied formal logic.
2) If you did not study formal logic, then your CR score will not behigh.

The second method is the foolproof way, which replaces unless with if not. The preferred way is the firstmethod, which negate the clause before unless andcap it with if,and replace unless with then. Basically the clause after unless is the necessary condition which musthappen for the negated form of the other clause. Back to the example we havehere, “study formal logic” is a necessary step for one to get high score in CR.Without “studying formal logic”, one would not be able to score a high mark inCR. But “studying formal logic” alone might not be sufficient to help you scorehigh in CR.

When the unless-clause comes at the beginning of the sentence, everythingbetween the word unless andthe comma is the unless-clause.


Either

The word either can also create an if-then relationship. Consider thisexample:
Either Peking University or Tshinghua University is on the list of mydream schools.

Given this rule, if PKU is not on my list, then THU is on my list because oneof them must be. Further, the rule does not exclude the possibility that bothschools are on my list. Therefore, the correct way to say the same thing usingif-then clauses is:
If PKU is NOT on my list, then THU is.
Notice the word NOT is added to the if-clause, not the then-clause.Otherwise, we would make the mistaken assumption that both schools cannot be onthe list together, which is not necessarily true—at least on the GMAT or LSAT.


Hiddenif-then statements

Many if-then statements on the test are hidden because they do not use if or then. Instead, they use words like all, any, when, must and so on. Consider thisexample:
All Chinese students are diligent.
Translation: If you are a Chinese student, then you are diligent. (Itruly hope so!!)

The trick here is that all means if.

There are also words that mean then. Here is another example:
Reading SDCAR’s posts on CR requires good understanding of English.
Translation: If you can read SDCAR’s posts on CR, then you have goodunderstanding of English. (Pat yourself on the back, please!!)

Here are more words you can use to find hidden if-then statements:

If: All, always, any, each, every, inorder to, invariably, no, none, things that, those who, to, when.

Then: Depends on, essential, must,necessary, needs, only, only if, only when, prerequisite, requires.

Unless (ifnot): Except, until, without.


No
When you see no atthe beginning of a sentence, change no to if and negate the other clause, which isyour then clause. Example:
No one who has a cold should go outside. (No X is Y.)
Translation: If you have a cold, then you should NOT go outside. (If X,then NOT Y.)


Most,some, and not all
Most means more than half. Most could be all.
Some means at least one. Some = Many. Some could be most,could be all.
Not all means some did not. Not all could be none.

SDCAR2010【逻辑入门】（十三）Formal Logic (1)

SDCAR2010【逻辑入门】（十五）More on Negation

Francischen0125

感谢LZ CR做得差 还得继续学  而且Assumption那一章节完全看不懂 呜呜呜

塔塔Carol

感谢分享！               

Jessica_ydy

感谢分享！               

梦季

Mark一下！               

梦季

感谢分享！               

sa0314

Mark一下！               

echogmj

thanks for sharing ~~~

fatbunbun

sdcar2010 发表于 2012-2-4 21:57
Suppose we have 100 people, then1) All = 100 people2) Many = between 1 and 100 people (inclusive)3)  ...

awesome!!!

sdcar2010

A unless B.
Translation: 1) If NOT B, then A; or 2) If NOT A, then B.

Not A unless B.
Translation: 1) If NOT B, then NOT A; or 2) If A, then B.

That's all you need to remember about the meaning of UNLESS.