lawyer语录里的那道充分型假设题~~求解~~~~

小唯唯

No mathematical proposition can be proven true by observation. Itfollows that it is impossible to know any mathematical proposition to be true.

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



(A) Only propositions that can be proven true can be known to be true


(B) Observation alone cannot be used to prove the truth of any proposition


(C) If a proposition can be proven true by observation then it can be known to be true.


(D) Knowing a proposition to be true is impossible only if it cannot be proved true by observation


(E) Knowing a proposition to be true requires proving it true by observation
正确答案是E。我弄了半天终于把逻辑关系搞清楚了，也终于知道E是和原题的逻辑方向一致了，但是，这不是一道假设题么？E只是同义重复了一下原题啊，并没有加入一个假设或者是什么条件啊？
求NN们帮忙解答~~

小唯唯

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sdcar2010

Premise: If math proposition, then observation cannot prove it true. (If A, then B)
Conclusion: If math proposition, then it is impossible to know it is true. (If A, then C)

Assumption: If observation cannot prove it true, then it is impossilbe to know it is true. (If B, then C)

The contraposition of the assumption is answer choice E. (If NOT C, then NOT B)

小唯唯

噫……不理解……

cycyang

No mathematical proposition can be proven true by observation. It follows that it is impossible to know any mathematical proposition to be true.
前提：任何数学命题都不能通过观察法来证明其正确性。结论：没有任何数学命题可以被证明是正确的。

如果这个结论成立，我们所缺的条件是：我们能并且只能通过观察法来证明命题的正确性，即Knowing a proposition to be true requires proving it true by observation.

这里的“assume”指的是如果结论成立，我们需要假设什么条件。这个条件本身是不需要假设的，通常是陈述一个事实。

小唯唯

Premise: If math proposition, then observation cannot prove it true. (If A, then B)
Conclusion: If math proposition, then it is impossible to know it is true. (If A, then C)

Assumption: If observation cannot prove it true, then it is impossilbe to know it is true. (If B, then C)

The contraposition of the assumption is answer choice E. (If NOT C, then NOT B)

-- by 会员 sdcar2010 (2011/3/13 21:24:40)

这样说要明白一些了……可是为什么要把math proposition作为IF的对象呢？这个不是这道题的范围么？所有的选项也都在说Math呀？

小唯唯

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