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Author Topic: LR Test #24 Section 2 Question 24  (Read 1163 times)

Dionysus0

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LR Test #24 Section 2 Question 24
« on: April 27, 2008, 03:56:51 PM »
I need some help on this question; most of the answers appear the same to me. Could someone please explain why the credited answer is the only correct one?

24. No mathematical proposition can be proven true by observation. It follows that it is impossible to know any mathematical proposion to be true.

The conclusion follows logically if which one of the following is assumed?

Correct answer (E) Knowing a proposition to be true requires proving it true by obervation.

My incorrect answer selected (C) If a proposition  can be proven true by observation, then it can be known to be true.

Extra points for someone who can explain what is wrong with the answer I selected.
Thanks.

EarlCat

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Re: LR Test #24 Section 2 Question 24
« Reply #1 on: April 27, 2008, 06:06:17 PM »
Premise: You can't prove it true by observation.
Conclusion: You can't prove it true at all.

E. Knowing it's true requires observation. 
Negation test: Knowing its true does not require observation.
Think: Oh, if I negate this, I might prove it true with something other than observation, so the conclusion no longer works.  TCR.

C. If it's proven by observation, then it can be known to be true.
Think: That's great, but couldn't there still be other ways to know something is true?

You can also try the negation test on C:  If it's proven by observation, it still might not be known to be true.  After negating, our conclusion (you can't know a math proposition is true) could still work.  Cross this one off.

A similar argument might be:
You can't go to the store in Donald Trump's 747 so you can't go to the store.

ssilver0210

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Re: LR Test #24 Section 2 Question 24
« Reply #2 on: April 28, 2008, 03:46:21 PM »
An analogy:

No person can score a 180 on the LSAT while wearing a green hat. It follows that no person can score a 180 on the LSAT.

Now, it should be fairly obvious that the conclusion that no person can score a 180 on the LSAT is flawed based on the other information provided. Even if it's true that no person can score a 180 on the LSAT if wearing a green hat, others who are not wearing a green hat might still have the ability to score a 180.

You're asked to find the statement which makes the conclusion true, or makes the conclusion follow logically from the statements. Let's say that every person who was to take the LSAT was required to wear a green hat (the equivalent of choice E).

Now we have the following statements.

No person can score a 180 on the LSAT while wearing a green hat.
All people are required to wear a green hat while taking the LSAT.
No person can score a 180 on the LSAT.

With the addition of the second statement (the equivalent of choice E), the conclusion now follows logically. That's why choice E in this particular problem was the correct choice.



Assume that

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Dionysus0

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Re: LR Test #24 Section 2 Question 24
« Reply #3 on: April 28, 2008, 09:22:30 PM »
I appreciate the responses. I have to remember to put the new term in the conclusion as the sufficient part in the conditional statement of the additional premise. Everyone gets point, but Jeffort gets all the bonus points for the detailed response and including a wookie? in his post.

EarlCat

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Re: LR Test #24 Section 2 Question 24
« Reply #4 on: April 28, 2008, 10:36:10 PM »
Uh oh, you jumped the shark on this one bro.  I have to pull rank here.  ;)

Woah, you're right.  I totally didn't read the question.  Yeah.  Ignore all that bullcrap I said (except the 747 thing...I still like that).