分享一道逻辑题，求解析

echomaotw

prep07的一道逻辑题，有人能够解释下这道题为什么选b吗？题目的最后一句话没看懂。谢谢

59.   (33759-!-item-!-188;#058&007597)

Bank depositors in the United States are all financiallyprotected against bank failure because the government insures all individuals'bank deposits.  An economist argues thatthis insurance is partly responsible for the high rate of bank failures, sinceit removes from depositors any financial incentive to find out whether the bankthat holds their money is secure against failure.  If depositors were more selective, then bankswould need to be secure in order to compete for depositors' money.

Which of the following, if true, most seriously weakens theeconomist's argument?

(A) Before the government started to insure depositorsagainst bank failure, there was a lower rate of bank failure than there is now.

(B) When the government did not insure deposits, frequentbank failures occurred as a result of depositors' fears of losing money in bankfailures.

(C) Surveys show that a significant proportion of depositorsare aware that their deposits are insured by the government.

(D) There is an upper limit on the amount of an individual'sdeposit that the government will insure, but very few individuals' depositsexceed this limit.

(E) The security of a bank against failure depends on thepercentage of its assets that are loaned out and also on how much risk itsloans involve.

carandl

我刚好也在搜索这道题，看到了你的问题。下面是我搜索各网站信息后的解读.
首先，这道题就是问的assumption, 只是换了个方法提问。
题干的焦点是depositor与bank的关系，此题中说government导致了failure,因为it removes from depositors any financial incentive to find out whether the bank that holds their money is secure against failure。E选项就是对上述句子重述的assumption。

另外，有段外文的解答很好，你可以看看：
one of the common ways that GMAC want to test you is find out the alternative cause for the observed effect.
a. observed effect: high rate of bank failures
b. cause that economist claimed: goverment insurants
c. find out the alternate cause

echomaotw

谢谢你的回复，但答案是B

我也找了一个解析，感觉有点道理
choice (b), in essence, shows that a high rate of bank failures would persist even in the absence of deposit insurance -- thus weakening the idea that the insurance is responsible for the high rate of failure.

i don't totally love this connection, because, rather than directly weakening the argument, it basically says, "well, something else would cause the same effect anyway if you took thing X away."
on the other hand, fortunately, the process of elimination is rather straightforward here on the other choices.

* choice (a) is strong supporting evidence for the argument, not evidence against it.

* choice (c) really doesn't do much one way or the other -- but the opposite of this statement would weaken the argument. i.e., if depositors were unaware of the insurance, then the economist's argument would fall apart. so, if the opposite of this choice does what we want, then this choice is not what we want.

* choice (d) says that the government will refuse to insure above a certain amount (say, i don't know, $1 million). but then it says that very few individuals' deposits are above this level anyway -- so this choice is basically irrelevant.
remember, the economist's argument is about the behavior of depositors in general; therefore, any statement that's limited to a small number of people is not going to have an appreciable effect on such general trends.

* choice (e) is irrelevant, since the argument is not concerned with things about the banks themselves that make the banks more susceptible to failure; rather, it is concerned with the behavior of the banks' depositors.

alzn2765

这道题有好几个变形，你这个是其中一个。

其实这题你之所以没明白是因为你没找准前提和结论，因为看你问最后一句话没读懂就知道了。
其实本题的前提和结论根本不在最后一句，你不看也不影响做这道题。

前提（果）：High rate of bank failures
结论（因）：government insurance bank against failure

果因推理加强套路是：非因--->非果 （等价逆否命题）

削弱
就是：非因 交 果（A-->B的有效否定是A交非B，基础逻辑理论）


B选项逻辑为：when NO government insurance 同时发生 bank failure
这就是 非因 交 果 的削弱

要是换成通俗易懂的“人话”就是：政府保险是银行倒闭的原因，如果我们发现没有政府保险的时候银行一样倒闭是不是等于削弱了“政府保险是银行倒闭的原因”？

要是这个例子难理解可以换成等价的容易理解的例子：A的女朋友说A跟她XXOO了是导致她怀孕的原因。结果我们发现A跟她XXOO之前，她就已经怀孕了。你说A的女朋友是不是在给A扣屎盆子？

alzn2765

echomaotw 发表于 2015-8-6 00:53
谢谢你的回复，但答案是B

我也找了一个解析，感觉有点道理

这种排除法缺乏逻辑理论基础支持，几乎是在靠感觉做题，不推荐。

qsgmat

alzn2765 发表于 2015-8-6 10:12
这道题有好几个变形，你这个是其中一个。

其实这题你之所以没明白是因为你没找准前提和结论，因为看你问最 ...

我的逻辑链是：
经济学家认为：政府insurance--->导致银行破车
B的意思是， 没有这个insurance的时候，不管什么原因，银行也破了
所以说有没有这个insurance 银行都破产，也就是说 insurance不是破产的原因，一定有他因致使银行破产。

所以削弱