在虚拟条件句中的运用
1. 与现在事实相反：条件句的谓语动词用一般过去式(be一般用were) ，主句谓语用would /should /could /might +动词原形。如：
If I were you， I would never do that. 如果我是你，我决不做那件事。
If it weren’t for (=But for) your help， I would still be homeless. 若不是你帮忙，我现在还是无家可归。
If I had more money， I would buy a car. 我要是有再多一点钱，我就买汽车了。
注：在口语中，在diyi、三人称后，也有人用was。如：
If I was(were) rich， I would buy a car. 我要是有钱，我就买汽车了。
2. 与将来事实相反：条件句中的谓语可用一般过去式、或者“were to /should＋动词原形”，主句谓语用would /should /could /might +动词原形。如：
If it rained/should rain/were to rain tomorrow， I would not go there. 要是明天下雨，我就不去那里。
3. 与过去事实相反：条件句的谓语动词用过去完成式，主句谓语用would /should /could /might + have +过去分词。如：
If he had taken my advice， he might not have made such a bad mistake. 要是他当初听从我的劝告就不会犯这么严重的错误了。
If it hadn’t been for Margaret， I might not have understood. 要不是有玛格丽特，我可能还不明白。
注：若虚拟条件句中有were， should， had时，可省略if，将were， should， had移至主语前。如：
Were I you， I would never do that.
Should it rain tomorrow， I wouldn’t go there.
Had it not been for Margaret， I might not have understood.
■在错综时间虚拟条件句中的运用
虚拟条件句与主句谓动词发生的时间有时不一致，要注意主从句谓语动词的形式。如：
If you’d listened to me， you wouldn’t be in such trouble now. 如果你当初听了我的话，你现在也不会有这样的麻烦了。
■在含蓄虚拟条件句中的运用
有时只有主句，不出现虚拟条件句，而是用without， with， but for(要不是) 等介词短语，或者用but， or， otherwise等副词或连词，或者用不定式或分词短语等来表示虚拟条件。如：
But for (=if it had not been for ) your help， I wouldn’t have been successful. 要是没有你的帮助，我就不会成功。
I was so busy then， otherwise， I would have helped him. 我当时很忙，要不然，我会帮助他的。
We couldn’t have finished it without Mary. 如果没有玛丽，我们是不能按时完成这个工作的。
To hear him talk (=If you could hear him talk…) ， you’d think he was Prime Minister. 听他讲话你会以为他是首相。
Given more time， I could have done it better. 要是多给一点时间，我会做得更好。
■在wish， if only， as if， would rather等后的从句中
这些从句的谓语动词的形式是：若与现在或将来事实相反，用一般过去式(动词be一律用were) ；若与过去事实相反，用过去完成式。如(www.yygrammar.com)：
I wish it were spring here all the year round. 但愿这里四季如春。
I wish I hadn’t wasted so much time. 但愿当初不该浪费这么多时间就好了。
If only she would go with me! 她要是愿意和我一道去就好了!
If only I had listened to my parents! 我要是听了我父母的话就好了。
Li Ming speaks English as if he were an American. 李明说英语好像是美国人。
I would rather he came tomorrow. 我宁愿他明天来。
I’d rather he hadn’t told me about it. 我宁愿他没告诉我这事。
注：as if/as though引导的从句若是事实，就不必用虚拟语气。如：
It looks as if it is going to rain. 看起来要下雨的样子。
■ as if/as though引导的从句中
He speaks English as though he were an American. 他说英语跟美国人差不多。
■在It’s time that…的that从句的谓语动词
It is time that we got ready for the final examination. 该是我们为期末考试做准备的时候了。
