关于之前有人问到的either or 的问题~

taoransk · 发表于 2010-9-20 11:46:52

花了点时间,整理了下相关答案, 希望对大家有所帮助拉

原帖 http://forum.chasedream.com/LSAT/thread-464456-1-1.html#last

either or 根据conditional reasoning 和 formal logic 两部分的综合结果是

一个推理型陈述题干里, 每个逻辑关系都有一个sufficient和一个necessary的区别, sufficient出现意味necessary即将或已经,总之必然出现,但并不直接造成其激发. either or的作用在于,两个问题是并列的(formal logic里的并列分and / or) ,所以在无其他因素的情况下,这两个都可以又做sufficient又做necessary.

举个例子

The dinner won't be ready untill all dishes have been prepared

这里前面一部分是sufficient,后面一部分是necessary. 如果晚餐好了,那么意味着必然所有菜都准备好了, 但是所有菜准备好了不代表晚餐必然好了.

插一下, 两个单元部分着重说了关于对换句的问题, 这里简单说下结果
Dinner Ready ----> Dishes have been prepared
标准对换句是
Dishes have been prepared (X) ----> Dinner Ready (X)

好了现在把例子代入either or

I am either Chinese or Canadian

Chinese (X) ----> Canadian
or
Canadian (X) ----> Chinese

不是中国人就是加拿大人, 不是加拿大人就是中国人

这里表现了如果不是一个国籍,那么一定是另一个国籍,好像下面摘录里陈述的, at least one of the two, 但是这里,并没有包括一个可能,就是我也可以是双重国籍,那么两个都存在, 这就是原来那位仁兄提出的both问题, 而这个问题在S/N逻辑关系里是无法表达的, 我们只能记住必须出现一个, 但是出现一个的结果是另一个可以出现或不出现, 但是无法强制

然后,这里要提到另一个问题了,限定

I am either at London or New York

上面那个例子里, 国籍是有双重可能的, 但这里, 伦敦和纽约是地球人都知道的两个城市, 所以显然一个人不可能同时在两个地方出现
虽然在很多情况下LSAT要求不要代入除了题目给出信息之外的其他知识, 但是也是有例外的, 这里就是一个, 至少, 出题的是严格的人, 但不是笨蛋. 所以, 这种情况是common sence, 而应该被注意到. 这个问题在综合了整本书后, 有两种可能, 一个是common sence, 一个是如果使用的方式是 either... or... , but not both, 也就是说, 这两种情况下, but not both是自动起作用的

那么, 上面那两重的S/N关系就变成了:

London (X) ----> New York
New York (X) ----> London

London ----> New York (X)
New York ----> London (X)

... ...

In the everyday use outside of the LSAT, 'either/or'has come to mean 'one or the other, but not both', but this usage isincorrect on the LSAT. For the purposes of the test, the definition of'either/or' is 'at least one of the two',Note that this definition implicitly allows for the possibility thatboth elements occur, and the existence of this possibility makesdiagramming sentences containing the 'either/or' term confusing. Acareful examination of the definition of 'either/or' reveals that aconditional relationship is at the heart of the construction: since atleast one of the terms must occur, if one fails to occur then the othermust occur.

... ...

Tofurther complicate the issue, occasionally our 'outside' (but publicdomain ) knowledge of the elements involved the 'either/or' constructallows us to make additional inferences,
Eg. You are either in Los Angeles or Sanfrancisco

... ...

according to 'either/or' term, the statement is diagrammed as follow:

LA X -> SF
SF X -> LA

... ...

butwe also know that if you are in one of the cities, then you are not inthe other. However, this knowledge does not come to us from the'either/or' term above, but from our public domain knowledge ofgeography. Thus, another set of diagrams may apply:

LA -> SF X
SF -> LA X

... ...

Notethat makers of the LSAT could creat a statment about two fictional orlittle-known cities, such as 'You are either in Monroe or Tipiwanee'.Whthout being provided further information about these cities, we couldonly diagram for the 'either/or' term, A diagram that attempts toreflect geographic knowledge such as :

Monroe -> Tipiwanee X

would not apply since we cannot be sure that Monroe and Tipiwanee do not overlap geographically

.....

关于之前有人问到的either or 的问题~

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