充分必要条件指示词

lawyer_1

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)

robertchu

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".  

leeon

I do't think there are any causal effects in the sentence "no citizen can be denied the right to vote."

leeon

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.

[此贴子已经被作者于2004-10-15 14:16:27编辑过]

leeon

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

paopao

以下是引用robertchu在2004-10-15 12:56:00的发言：

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.

lawyer_1

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。

robertchu

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).

timeaway

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

timeaway

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.