虚拟语气的含蓄条件句的运用
请问，虚拟语气的含蓄条件句怎么样运用？
其他语法书和网页上说明含蓄条件句都只是“用一些例句来列举说明含蓄条件句有多少种情况”而已，但没有教会怎么运用含蓄条件句：是用介词短语、不定式等代替if条件句的哪一部分而构成含蓄条件句的。我希望高手们能列举含蓄条件句的一些构成规则，谢谢！
请问，怎么判断是对哪个时间的虚拟，然后怎么仿照if引导的句式结构呢？请高手具体说明。
很多情况下，在表示假设的虚拟语气中，有时假设的条件并不以条件从句的形式表达，而是通过上下文或句中内在的逻辑关系，或用其它形式表达出来。
含蓄条件句主要通过名词、连接词、不定式、分词、动名词短语、介词短语及分句来暗示。这些表达形式在句中实际起着虚拟条件从句的作用。
含蓄条件句的虚拟时间：
含蓄条件句是一种不出现条件从句的句子，也就是说它只是单独的一个主句形式，因此谓语动词就是主句所要求的形式：
1、表示对过去的虚拟：情态动词 would/could/should/ought to + have done；
2、表示对现在或将来的虚拟：情态动词 would/could/should/ought to + do。
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第1个回答 2010-06-04
含有but for/without/otherwise/or／unless/if only/what if的句式
But for the help of the firefighters, the factory wouldn’t have been saved.
Without air, there wouldn’t be any living things on earth.
I was so busy then, otherwise, I would have finished it.
It rained yesterday, or I would have gone camping.
I would not change my mind unless the sun were to rise in the west tomorrow.
If only I were a bird now!
What if I were busy?
But for the help of the firefighters, the factory wouldn’t have been saved.
Without air, there wouldn’t be any living things on earth.
I was so busy then, otherwise, I would have finished it.
It rained yesterday, or I would have gone camping.
I would not change my mind unless the sun were to rise in the west tomorrow.
If only I were a bird now!
What if I were busy?
第2个回答 2010-06-06
含蓄条件句：
虚拟语气句中不出现if条件句，而是利用介词或介词短语、分词短语，不定式或连词通过上下文表现出来。这时，须根据句子的含义来判定是用虚拟现在式还是虚拟过去式。
（1）介词或介词短语：but for,without,with,under
But for the rain, we should have a pleasant journey.
Without air, there would be no living things.
With favorable winds,we might have got there in tow days.
We could have done better under more favorable conditions.
（2）分词短语，
This same thing, happening in wartime,would amount to disaster.
（3）不定式短语
To hear him speak English, one would take him for a foreigner.
（4）连词：but,but that,or或otherwise
主句（虚拟语气）+but/but for(若不是)+从句（陈述句）
解释：主句是没有发生的事情，所以用虚拟语气；从句表示的是事实。
He wold have given you more help,but he was so busy.
(如果他不是那么忙，他会帮你更多的忙。“他忙”是事实，用陈述语气，但他并没有帮你更多的忙，用虚拟语气）
同理：
主句（陈述语气）+or/otherwise(否则)+从句（虚拟语气）
She eats too much every day,or she would be thinner.
(她每天都吃很多，否则她会瘦一点。她吃得多是事实，用陈述语气，她实际没有瘦，用虚拟语气）
建议你看复旦大学出版社的英语语法实践指南，很详细的
虚拟语气句中不出现if条件句，而是利用介词或介词短语、分词短语，不定式或连词通过上下文表现出来。这时，须根据句子的含义来判定是用虚拟现在式还是虚拟过去式。
（1）介词或介词短语：but for,without,with,under
But for the rain, we should have a pleasant journey.
Without air, there would be no living things.
With favorable winds,we might have got there in tow days.
We could have done better under more favorable conditions.
（2）分词短语，
This same thing, happening in wartime,would amount to disaster.
（3）不定式短语
To hear him speak English, one would take him for a foreigner.
（4）连词：but,but that,or或otherwise
主句（虚拟语气）+but/but for(若不是)+从句（陈述句）
解释：主句是没有发生的事情，所以用虚拟语气；从句表示的是事实。
He wold have given you more help,but he was so busy.
(如果他不是那么忙，他会帮你更多的忙。“他忙”是事实，用陈述语气，但他并没有帮你更多的忙，用虚拟语气）
同理：
主句（陈述语气）+or/otherwise(否则)+从句（虚拟语气）
She eats too much every day,or she would be thinner.
(她每天都吃很多，否则她会瘦一点。她吃得多是事实，用陈述语气，她实际没有瘦，用虚拟语气）
建议你看复旦大学出版社的英语语法实践指南，很详细的
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