关于unless的用法等3问题心得

mzyzhu · 发表于 2003-6-11 16:00:00

T18/S4/Q9. Any person who drops out of high school will be unemployed unless he or she finds a low-paying job or has relative with good business connections.

9. Which one of the following conclusions CANNOT be validly drawn from the statement above?

(A) Any person who drops out of high school will be unemployed, have a low-paying job, or have relatives with good business connections.
(B) Any high school dropout who has neither a low-paying job nor relatives with good business connections will be unemployed.
(C) Any employed person who has neither a low-paying job nor relatives with good business connections is not a high school dropout.
(D) Any high school dropout who has a job that is not low-paying must have relatives with good business connections.
(E)Any person who has relatives with good business connections and who is not a high school dropout must be employed at a job that is not low-paying.

本题有3个重点：(1)unless的用法; (2)定于从句=充分条件if; (3)主语和宾语均为带定于从句的符合从句的逆否命题的理解。

（1）unless的用法。According to MW dictionary, unless= without, but how to use the explanation in the real test is not easy. 通过我的一些实践，我认为以后碰到unless问题可作如下展开。原句：not A unless B = not A if not B or if A then B. 为必要条件。提干展开后就变为：

A PERSON if he/she is a high-school drop-out will UNEMPLOYED IF without low-paying job and IF without relatives with good relationship, OR IF A PERSON who is a high school drop out is EMPLOYED THEN either the job is a low-paying or good relatives exist.

A说的就是展开后的原文。

B 说的就是加下划线的部分A PERSON if he/she is a high-school drop-out will UNEMPLOYED IF without low-paying job and IF without relatives with good relationship, OR IF A PERSON is EMPLOYED THEN either the job is a low-paying or good relatives exist.。

C 说的就是加下划线的部分A PERSON if he/she is a high-school drop-out will UNEMPLOYED IF without low-paying job and IF without relatives with good relationship, OR IF A PERSON who is a high school drop out is EMPLOYED THEN either the job is a low-paying or good relatives exist. 但是这里说的不是原命题，而是逆否命题。体会这里的AèB, no Bèno A. A employed neither lowing paying nor good relationshipèperson who is not high school drop out

D 说的就是加下划线的部分A PERSON if he/she is a high-school drop-out will UNEMPLOYED IF without low-paying job and IF without relatives with good relationship, OR IF A PERSON who is a high school drop out is EMPLOYED THEN either the job is a low-paying or good relatives exist. 继续表达原文：high school drop out…has a job but is not low-paying…must have good relatives.

E 只有E：Any person who has relatives with good business connections and who is not a high school dropout must be employed at a job that is not low-paying. 推不出来。其主要意思是A person who… and who … be employed that…. 我们回到原句找相关下划线部分A PERSON if he/she is a high-school drop-out will UNEMPLOYED IF without low-paying job and IF without relatives with good relationship, OR IF A PERSON who is a high school drop out is EMPLOYED THEN either the job is a low-paying or good relatives exist.

[此贴子已经被作者于2003-6-14 2:06:08编辑过]

jacy · 发表于 2003-6-11 18:05:00

（1）unless的用法。according to mw dictionary, unless= without, but how to use the explanation in the real test is not easy. 通过我的一些实践，我认为以后碰到unless问题可作如下展开。原句：a unless b = not a if b or a if not b.

sorry, 我认为这样想有问题，
a unless b=if not b，then a
即：非b--〉a
也就是：非a--〉b
a unless b不等于not a if b

albert · 发表于 2003-6-11 21:08:00

我的体会：

1.
a  unless b  等价于  not a --> b
a  until b 一样 not a --> b
我一般做题目的时候理解成： b 是 not a 的必要条件

2. if a then b
a , therefore b
a then b
a so b
if only a , b
  .......
a--> b a 是 b 的充分条件
3. only b, a
a--> b  b是必要条件
4.  only and if only a ,then b
  充分必要 a--> b , b--> a

LSAT常考：

1：只有逆否命题和原命题等价

2: 充分当成了必要。
a----> b  那么  非a 推不出非B  只有非B推出非A
也就是只有必要取非，结论才不成立
如果我考800，我一定睡不着觉。。可是我不能考800，我睡得很香。。很错误的逻辑

3: 必要当成里充分
a----> b  那么 b---> a
如：要刻苦才能考800。可是不是说我刻苦了我一定考800。。

还有很多，一下想不起来了。。想起来再补充。。也请大家补充。。

mzyzhu · 发表于 2003-6-11 21:51:00

[此贴子已经被作者于2003-6-14 2:02:08编辑过]

关于unless的用法等3问题心得

关于unless的用法等3问题心得

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