大家来试试这道题练习一下思维

leadwest · 发表于 2009-11-22 21:42:08

选自LSAT Section IV -22

All intelligent people are nearsighted. I am very nearsighted. So I must be a genius.

Which one of the following exhibits both of the logical flaws exhibited in the argument above?

A. I must be a stupid because all intelligent people are nearsighted and I have perfect eyesight.
B. All chickens have beaks. This bird has a beak. So this bird must be a chicken.
C. All pigs have four legs, but this spider has eight legs. So this spider must be twice as big as any pig.
D. John is extremely happy, so he must be extremely tall because all tall people are happy.
E. All geniuses are very nearsighted. I must be very nearsighted since I am a genius.

[D] is the correct answer. Let's discuss why.

chanelzr · 发表于 2009-11-22 22:29:08

The logical flaws of this argument are:
First，"all intelligent people are nearsighted" cannot be interpreted as "if people are nearsighted, they are intelligent". Because we know "If A, then B" cannot draw "If B, then A".
Second, there is no positive correlation between the degree of "nearsighted" and the that of "intelligent".

Let's look at the answers:
A) "If intelligent, then nearsighted." can be decoded as "If not nearsighted, then not intelligent". (contra-positive)
eliminated
B) only contains the first logical flaw
eliminated
C) "So the spider must be twice as big as any pig" shows the comparison of the size which is irrelevant.
eliminated
D) "All tall people are happy" = If tall, then happy
"John is extremely happy, so he must be extremely tall" = If extremely happy, then extremely tall"
EXACTLY SAME AS THE ABOVE ARGUMENT!!!
E) only contains the first logical flaw
eliminated

What's ur opinions?

leadwest · 发表于 2009-11-22 22:38:48

First flaw in the argument is that the author mistook "necessary condition A<=B" for "sufficient condition A=>B". I agree with you.
Thanks for your explanation about the second flaw.. Initially I just got some feeling about "degree" but I didn't have confidence that it is a flaw. Now I fully agree with you.. thanks..

chanelzr · 发表于 2009-11-22 23:51:08

别客气，你几号三战呀？

大家来试试这道题练习一下思维

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