充分必要条件指示词
1.introduce a sufficient condition: if/when/whenever/every/all/any/people who/in order to/to
2.introduce a necessary condition: then/only/only if/must/require/no,none(在句子开头)
3.unless equation: unless/except/until/without(其后面部分变成必要条件，其它加NOT变充分条件)
4.特例：the only way to achieve success is to work hard. achieve success(充分条件)
only a professional consultant can solve the organization’s problems. a professional consultant(必要条件)
no citizen can be denied the right to vote. denied the right to vote(充分条件). no citizen(必要条件)
好贴。
"no citizen can be denied the right to vote. denied the right to vote(充分条件). no citizen(必要条件)"
??? 不懂。
I would say "citizen" is a sufficient condition for "right to vote".
An example to the required condition word, not until A, B,
Teachers are effective only when they help their students become independent learners. Yet not until teachers have the power to make decisions in their own classrooms can they enable their students to make their own decisions. Students’ capability to make their own decisions is essential to their becoming independent learners. Therefore, if teachers are to be effective, they must have the power to make decisions in their own classrooms.
According to the argument, each of the following could be true of teachers who have enabled their students to make their own decisions EXCEPT:
(A) Their students have not become independent learners.
(B) They are not effective teachers.
(C) They are effective teachers.
(D) They have the power to make decisions in their own classrooms.（E）
(E) They do not have the power to make decisions.
We can change the sentence to "teachers can not enable their students to make their own decisions until they have the power to make decisions in their own classrooms".
not until A B= not B until A, B-->A
好贴。
"no citizen can be denied the right to vote. denied the right to vote(充分条件). no citizen(必要条件)"
??? 不懂。
I would say "citizen" is a sufficient condition for "right to vote".
if he is a citizen, he has the right to vote.
agree with robert, citizen is a sufficient condition.
1。denied the right to vote(充分条件)——〉no citizen(必要条件)。即citizen——〉right to vote （逆否命题），所以ROBERCHU兄说的其实一样，只是原文的逆否命题。不要看丢RIGHT前还有个DENIED。
2。no citizen can be denied the right to vote. denied the right to vote. 即All citizen can NOT be denied the right to vote。即IF citizen， THEN canNOT be denied the right to vote. 即IF citizen,THEN right to vote。
I would say "(being) denied the right to vote" is a sufficient condition for "not (being) a citizen" (instead of "no citize").
So I agree with lawyer in principle (the logic), but slightly differ with him on the wording (措辞).
the words used in logical conditions are collected by me such as:
1 sufficient condition ,if / if only A A is the sufficient condition in the argument. Like Aà
2 necessary condition,then/only if/ must by/require/draw on/depend on/relf on/base on B B is the necessary condition in the argument. Like àB
3 flexible words:
1. unless/until/without/except B B is the necessary condition in the argument. Like àB
2. But when added a ‘NOT’ in the rest part of the argument , the condition B will be changed into sufficient condition, Like Bà
***The reason is that when there is a ‘not ’ in the argument, we can present the argument as ‘非Aà非B’ .That is the same as ‘B àA’.***
And ask a question, is the argument such as ‘A, NOT unless B’ equal to ‘NOT A, unless B’?
Thanks
对特例的理解：
the only way to achieve success is to work hard. = only if 'work hard'(A), then 'achive success'(B). So B-->A
only a professional consultant can solve the organization’s problems.=only if a professional consultant, then .....(必要条件)the same as the first one sentence.
no citizen can be denied the right to vote. = if ' no citizen', then'be denied the right to vote' ?? 那么就是：逆否命题：have the right to vote à he is a citizen.
Hello, whoever can help me to get the right answer for the last sentence?
i think 'no citizen' is the sufficient condition for the 'be denied the right ';
so identical argument is 'have the right ' is the sufficient condition for 'is a citizen' .
1。No A is B=all A are not B: 实际上这时A和B是两个不相交的圈圈。
2。All A are not B=If A, then not B
3。同意了上面两点，就能明白原文的那句话。No citizen（A） can be denied the right to vote（B）
根据1，2。这句话就等于if citizen(A), then not be denied the right to vote(not B)。即if citizen(A), then HAVE the right to vote(not B)。充分条件是citizen，必要条件是have th right to vote。逆否命题：If be denied the right to vote, then no citizen。充分条件是be denied the right to vote。必要条件是no citizen。
希望你没给转晕了。
hehe, thanks lawyer_1.
I see what you said.
可以这样理解吗？就是要转为if..then..前提是要把A前面的all条件转换出来。? 嗯，我的意思是，all A .......才能用if A .then..。因为，如果A其实就是要求所有的A都有这个性质。
而我原来的转换是，直接针对no A.... 所以直接转为if no A, then...
请问你能给一个转换为if...then...的要求概括吗？
many thanks
lawyer 的确总结的很好，但对于lawyer的in order to / to 的充分性我有不尽相同的看法：
在must by A, in order to B中，in order to后为充分条件，must by后为必要条件，即应为B--》A。这点看法与lawyer相同
但在A, in order to B中，我认为in order to 后应该为必要条件，即A--》B。
比如：我存钱为了买房，应该理解为“存钱A--》买房B”，但如果倒着说：“买房B--》存钱A”则不对，因为买房我也不一定非得存钱，我可以贷款、可以找人借钱。
希望能够与大家讨论。不知道lawyer是否已经成功留学？
谢谢！
不过对其中的except 的充分必要还不是很了解，举个例子，请LAWYER看看是不是这样的：
Everyone went to movie except me.
（充分条件） not everyone went to movie –-- （必要条件）我没去 （这个必要条件好像非得也加否定才成立？）
（充分条件）我没去 – （必要条件） 每个人都去了
不当之处请指出。
1。你举的例子没有充分必要关系
2。即使有，按公式，应该是：not everyone went to movie--->I went
我的这块砖终于引来了Lawyer的玉，呵呵！
我的水平太菜, 举的例子不好。能不能请lawyer gg举个关于except 的例子呢？
1。你举的例子没有充分必要关系
还有疑问：这些充分必要条件指示词是在某些特定条件下使用的，还是有普遍意义？
还有一个困惑是：我记得费费上课时曾经讲过：plan A to B 及 do A in order to B, 这里的A与B构成充分必要关系，但是你说：
你举的例子没有充分必要关系。主句没有出现Must时，多为这种情况，就是没有充分必要关系。 好像有矛盾呢？
I am looking up
you are showing up
and then we both cheering up
'coz the problem has been ended up
But what i can do now is only up up up......
趁Lawyer gg在，我就打破沙锅啦！
记得你说过充分必要是指：如果A发生，则B发生。想问下：这里的B是指作为A必然发生的结果么？
如你举的例子， I plan to write GMAT in order to go to US . 因为即使write GMAT也不一定能够go to US，所以不存在充分必要关系。这么理解对么？
另外，能不能请GG再举个关于except的例子呢？（我举的例子说明不了问题：））
唉，我什么时候能象GG这样就好啦！像GG这样的强人，估计学校们要打破头来抢呢！
1。你的例子是：A的发生表示B一定发生(过去，现在或将来都可以)，并不是导致，否则变为因果关系
2。You can not get a high score in GMAT, except you visit CD 24 hours per day。get high score--->visit CD 24 hours per day.
太谢谢啦！一个困惑的问题终于解决！
应该说因果关系也是属于充分必要关系中的吧。
以下为Lawyer 关于偶的关于充分必要性问题的耐心解答：
刚送走一帮人，才看到GG的回复贴子。虽然你说得很清楚，可我这死脑筋还没转过弯来：为什么说因果关系就没有推理关系呢？因为拉登是恐怖分子，所以老美要抓他。这里没有推理么？延伸开来，在做罗辑题时，是不是只有GG归纳的几个词才有这种推理关系，之外的都没有呢？
拉登是恐怖分子，不是美国就一定要抓他。又比如因为你学习努力，所以GMAT考了800分。只是说明你考800分的原因。但不是说你努力就一定能考800分。努力只是你考800分的其中一个原因，还要你聪明，考试那天去考，那天身体好，等等。如果一努力就能考800分，岂不是ETS要关门。
现在总算是明白了！A与B之间的充分必要关系是指它们之间的必然的相互联系（不论时间的前后），而因果关系间没有必然的联系。
再把自己的一点小想法补充下，请看看对否：象should / depend on / rely on / base on 是不是也是必要条件指示词？
depend on/rely on/base on indicate necessary condition. SHOULD indicate nothing. It just suggests you sth. It depends on you whether you follow the suggestion.
我的一点看法，请参考：
not A, until B: A—>B (The party won’t start until everyone is here.)
A, until B: ~A—>B / ~B—>A (The party will go on until everyone leaves.)
不懂，请详细解释一下。谢谢！ |
因果关系有时间概念
推理关系不存在时间概念
this discussion enables me to grasp the essence of the "sufficient and necessary condition".up up
SHOULD indicate nothing. It just suggests you sth. It depends on you whether you follow the suggestion.
an idea cited from ring_cheng
yet, the SHOULD, i think, indicate something.
one should do A to get B. B---A necessary
should A exist, then B A----b sufficient
汗阿 哦逻辑太差， 看了才知道这么多九九啊 顶
看是看明白了，可是一到做题，根本顾不上想！每次都是凭感觉．．．．
up..
可否舉個簡單的具體例子說明: 有因果关系,卻沒有推理关系.
3xs...
可否舉個簡單的具體例子說明: 有因果关系,卻沒有推理关系.
3xs...
比如：因为下雨，所以今天没有上课。
‘下雨’导致了‘没有上课’，下雨一定要发生在不上课之前，先因后果，即时间上有先后关系。
但是下雨并不一定会导致不上课(也就是说下雨不是不上课的充分条件），不上课也不一定就是下雨造成的（即下雨也不是不上课的必要条件），所以下雨和不上课之间没有必然的逻辑（推理）关系。
供探讨。
比如：因为下雨，所以今天没有上课(句1)。
‘下雨’导致了‘没有上课’，下雨一定要发生在不上课之前，先因后果，即时间上有先后关系。
但是下雨并不一定会导致不上课(句2)(也就是说下雨不是不上课的充分条件），不上课也不一定就是下雨造成的(句3)（即下雨也不是不上课的必要条件），所以下雨和不上课之间没有必然的逻辑（推理）关系。
供探讨。
小妹就snowfield GG 的例子, 整理幾點如下:
(1) 句1是因果關係; 句2及句3 是推理關係.
(2) 因果關係是推理關係中的一個特例,發生在"原因"="充分條件"之時. (要不然,此因果關係就不會成立了,不是嗎?)
請問可以這樣理解嗎?
盼指正...3xs.
我举的例子（句1）仅仅是对只有因果关系而没有推理关系的情况，所谓的句2/3只是我对例子（句1）的分析，并不是有推理关系的例子，换句话说对句2/3地分析并不利于MM理解逻辑关系和因果关系的区别。也许读一读前面NN的贴，并在做一些题目会有助于你的理解。
那请问snowfield，措施达目的型，是否可认为是充分必要条件：措施是充分条件，目的的必要条件？
楼主思维缜密,佩服!
学习一下.
many thanks.We all preiciate the help from lawyer suma
up~~~
充分条件：所谓充分条件就是仅有这些条件就足以带来结果，无需考虑别的条件了。它是谁成立谁也一定成立，比如A—〉B，如果A成立，那么一定有B，即A是B 成立的充分条件。
必要条件：所谓必要条件就是没有这个条件结论一定不对。比如B—〉A成立，
那么A是B成立的必要条件。
ring_cheng 发表于 2005-5-24 23:26
not A, until B: A—>B (The party won’t start un ...
lawyer_1 发表于 2004-10-13 11:55
充分必要条件指示词1.introduce a sufficient condition: if/when/whenever/every/all/any/people who/in o ...
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