请教lsat18/s2/q11

mzyzhu · 发表于 2003-6-11 02:01:00

11. The situation has gotten worse. Unless Elizabeth goes I must go. But she will not go if I stay So we will both have to go.

What is the flaw in the reasoning above?

(A) The first claim, that the situation has gotten worse, is irrelevant.

(B) A possible course of action is overlooked

(C) It is assumed that staying is the same as not going.

(D) The conclusion refers to a possibility that is not explicitly referred to in any of the premises.
答案是B. 我推不出来。

unless = if not, I go if E not go, if I stay E not go, 如何就推出了we both go, 而且答案还是忽视了某条件。不明白。请指教，谢谢。

albert · 发表于 2003-6-11 02:27:00

The claim overlook the possibility that I go but Elizebeth stay, which does not conflict with information of context.

mzyzhu · 发表于 2003-6-11 03:07:00

好像还是不太明白，能不能再讲细一点，谢谢albert

mindfree · 发表于 2003-6-11 07:45:00

"Unless Elizabeth goes I must go" ==> I do not have to go --> Elizabeth goes.

"she will not go if I stay" ==> I stay --> She will not go.

Conclusion: Both go.

The conclusion leaves out one possibility that I go and E stays. So it is not necessary for both to go, given the conditions in the passage.

mzyzhu · 发表于 2003-6-11 15:05:00

thank Albert for the antecedent explaantion.

thank Midfree for the consecutive explanation.

I try to describe the full picture in detail:

Uless E goes I must go==>我俩只有一个去，但是我被动选择。原句可扩展为I go if E not go or I not go if E go. 有关unless 的用法我将在下一个贴子中贴出我的心得。

E will not go if I stay==>我俩都不去。

E must go unless I go是 another course of action==>我俩只有一个去，但是我主动选择。或者是你们所说的I go and/but E stay.

总而言之，落脚在both go is not necessary.

jacy · 发表于 2003-6-11 18:14:00

E will not go if I stay==>我俩都不去。

mzyzhu：我想你的理解有问题。
上述左边不能得出右边的结论。
E will not go if I stay=I stay--〉E not go
E will not go if I stay=E go--〉i do not stay
只能推出这两个结论

所以如果 I go 根据题目条件则不能得出任何结论

mzyzhu · 发表于 2003-6-11 20:07:00

jacy: thanks for the explantion.

E will not go if I stay=E go--〉i do not stay 恐怕不对。是不是犯了这个错误。A==>B, not A==>Not B

jacy · 发表于 2003-6-11 21:46:00

以下是引用mzyzhu在2003-6-11 20:07:00的发言：
jacy: thanks for the explantion.

E will not go if I stay=E go--〉i do not stay 恐怕不对。是不是犯了这个错误。A==>B, not A==>Not B

呵呵，
我想是你把充分和必要条件搞混了。
E will not go if I stay=I stay--〉E not go
我想你应该认为是对的。
那么E go--〉i do not stay 实际上是I stay--〉E not go的逆否条件，两者是可以互推的。
所以E will not go if I stay=I stay--〉E not go
即A--》B等价于非B--》非A

mzyzhu · 发表于 2003-6-11 22:03:00

jocy, you are right

请教lsat18/s2/q11

请教lsat18/s2/q11

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