（a）But for a half hour or so for lunch I am here all day. (Yeats)
(b) But for my brother's help I would not have finished the work. (LDCE)
句(a)(b)中的 but for 意义是否相同?
在句(a)中but for表示“例外”(除……之外)，在意义和用法上近似于except for，但没有后者用得普遍。在句(b)中but for表示“否定的条件”（要不是，如果没有），而且这种否定的条件是与事实相反的，因此，句子的谓语动词要用虚拟语气。请注意下列各句中but for在意义和用法上的区别：
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But for John they all died. (CGEL) 除约翰外,他们都死了。
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But for John they would all have died. (CGEL) 如果没有约翰,他们就都死了。类例:
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But for the sun's heat, nothing could live. 如果没有太阳的热量,任何生物也不会存活。
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But for the rain we should have had a pleasant journey. (ALD) 要不是那场雨,我们的旅游会是很愉快的。
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But for the storm we should have arrived earlier. (PEG) 要不是那场暴风雨,我们本会早点儿到的。
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But for your coming, I should have been very lonely. (McMordie) 如果那时不是你来了的话,我是会非常孤独的。
请做下面的英语试题：
- “You finally made it, didn’t you?” “Yes, ____ your help, I would not have succeeded.” A. but that B. but for C. but if D. thanks to (TOEFL)
. ____ the flood, the ship would have reached its destination on time. A. In case of B. In spite of C. Because of D. But for(全国六级,90.1-58)
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He might have been killed ____ the arrival of the police. (此题出得不好, 见 except for) A. except for B. but for C. with D. for(全国六级,95.6-46)
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____ the English examination I would have gone to the concert last Sunday. A. In spite of B. But for C. Because of D. As for(全国研考,91-16)