LSAT-2-4-21.

ambrosecelin

Efficiency and redundancy are contradictory characteristics of linguistic systems: however, they can be used together to achieve usefulness and reliability in communication. If a spoken language is completely efficient, then every possible permutation of its basic language sounds can be an understandable word. However, if the human auditory system is an imperfect receptor of sounds, then it is not true that every possible permutation of a spoken language’s basic language sounds can be an understandable word.

If all of the statements above are true, which one of the following must also be true?

(A) Efficiency causes a spoken language to be useful and redundancy causes it to be reliable.

(B) Neither efficiency nor redundancy can be completely achieved in spoken language.

(C) If a spoken language were completely redundant, then it could not be useful.

(D) If the human auditory system were a perfect receptor of sounds, then every permutation of language sounds would be an understandable word.

(E) If the human auditory system is an imperfect receptor of sounds, then a spoken language cannot be completely efficient.

答案选（E），我想知道D为什么不对？谢谢！

racing78

LSAT的題目具有高度推理性與邏輯驗證性，這種題目需要利用p->q的邏輯推理解題。

題目說：if any language is complete efficient, then its permutatyion is understandable

imply如果permutation is not understandable,就不是complete efficient

題目最後說人的聽覺不是完美接受器，所以無法完全瞭解，所以：

人的聽覺不是完美接受器->無法完全瞭解->不是complete efficient (E)

D無法由題目給的已知條件推出，因為P->Q不能推導出Q->

ciscogeek

D: 一个命题正确，但他的否命题不一定正确。

ambrosecelin

哦~~~是这样的...谢谢大家！！