GMAT 逻辑分析题 (21) - ChaseDream

sd大侠，看了你的解释还是有点不明白~if a statement is true, then the contrapositive is also logically true, but not the mistaken negation，这句话是什么意思？是说原命题是真命题，那么他的逆否命题（contrapositive）是真的，否命题（negation）不一定是真的~（是这个意思么？）(YES)
所以D只是为了支持Comparing oneself to NiuNiu or BenBen只是一个充分条件。(YES)
所以如果Comparing oneself to NiuNiu or BenBen是充分必要条件的话，那么他的否命题也是成立的，对么？(No. What I meant is that as long as the statement "if comparing to Niuniu, then you are depessed" is correct, its contrapositive statement "if you are not depressed, then you did not compared yourself to NiuNiu" is also correct.)

-- by 会员 clumsy123 (2011/8/8 16:58:21)

en, what i mean is that if the statement is true that comparing oneself to others is the ONLY way leading to self-belittling and belittling others, will the argument be logical and sound?

-- by 会员 clumsy123 (2011/8/8 23:04:15)

Yes, then the flaw is gone.

-- by 会员 sdcar2010 (2011/8/8 23:40:46)

Thks NN for这道经典题目。

If A ->B (A is a condition but not necessarily a sufficient condition leading to B) is true, then its contrapositive(逆否命题) 'No B ->No A' is true, while its negation(否命题) 'No A ->No B' is not true.
The reason why the negation(否命题) is false is that other possibilities leading to B are overlooked.

-- by 会员 AlohaDJ (2011/8/9 0:44:53)

X:In order to reduce the amount of plastic in landfills, legislatures should impose a ban on the use of plastics for packaging goods.
Y:Impossible Plastic packaging is necessary for public safety.Consumers will lose all of the safety features that plastic offers, chiefly tamper-resistant closures and shatterproof bottles.

Which of the following best describes the weak point in Y's response to X's proposal?

A. Y ignores the possibility that packaging goods in materials other than plastic might provide the same safety features that packaging in plastic offers.
B. The economic disadvantages of using plastics as a means of packaging goods are not taken into consideration.
C. Y attempts to shift the blame for the large amount of plastic in landfills from the users of plastic packaging to the legislators.
D. Y does not consider the concern of some manufacturers that safety features spoil package appearances.
E. Y wrongly assumes that X defends the interests of the manufacturers rather than the interests of the consumers.

OA: A.

Y's response to X's proposal depends on the assumption that if plastic packaging is safe, Non-plastic packaging is not safe.This reasoning is flawed as per what is mentioned in the quotes above. Choice A right points out the weakness of the flawed reasoning.