再问OG-48?

leeon

A researcher discovered that people who have low levels of immune-system activity tend to score much lower on tests of mental health than do people with normal or high immune-system activity. The researcher concluded from this experiment that the immune system protects against mental illness as well as against physical disease.

The researcher’s conclusion depends on which of the following assumptions?

(A) High immune-system activity protects against mental illness better than normal immune-system activity does.

(B) Mental illness is similar to physical disease in its effects on body system.

(C) People with high immune-system activity cannot develop mental illness.

(D) Mental illness does not cause people’s immune-system activity to decrease.（D）

(E) Psychological treatment of mental illness is not as effective as is medical treatment.

请问这道题答案的思路是什么？为什么B not cause A可以成为A cause B的假设！

有没有相关的题形？

meixiapeng

前提是 immune-system(A) 和Mental illness (b)之间有某种关系,结论是a->b.这样是有欠缺的,有可能是b->a的.

这是逻辑中典型的一类,要记住. 如果D not 去掉,很显然文中的结论是的不出来的.

leeon

以下是引用meixiapeng在2004-9-13 14:29:00的发言：

前提是 immune-system(A) 和Mental illness (b)之间有某种关系,结论是a->b.这样是有欠缺的,有可能是b->a的.

这是逻辑中典型的一类,要记住. 如果D not 去掉,很显然文中的结论是的不出来的.

这个不一定吧！将not去掉后，变成了原文结论的逆命题！和原文结论能否推导是无法影响的！这类题我知道逻辑上有，但为什么这样可以成为答案？有没有人能给出详细的解释？

bryan0806

我是取非来看

如果Mental illness cause people’s immune-system activity to decrease  那么tests 的结果就有解释了 进而反驳了

the immune system protects against mental illness as well as against physical disease这个结论

leeon

还有没有其它的解释？

cranberry

否命题和逆命题是等价命题

lawyer_1

这是谁是因，谁是果题型。原文由 low levels of immune-system activity 的人mental health 较差，得出结论说low levels of immune-system activity 是因，是它导致 low levels of immune-system activity 。但也有可能mental health 是因，是它导致low levels of immune-system activity 。D排除这种可能。故为答案

lawyer_1

同类型体

http://forum.chasedream.com/dispbbs.asp?boardid=24&id=68606&star=1#601724

lawyer_1

同题型

http://forum.chasedream.com/dispbbs.asp?boardid=24&id=43329&star=1#602096

leeon

Got it;

B not cause A的逆命题＝A not cause B, A not cause B的否命题＝A cause B;根据原命题的逆命题等价于否命题＝>A cause B等价于B not cause A！证明。

谢谢cranberry和lawyer_l