用过去式表示的虚拟语气
虚拟条件句的三种基本类型
 
条件句有真实条件句和非真实(虚拟)条件句两种。真实条件句所表示的假设是有可能发生的，而非真实条件句则通常表示一种假想，与事实相反或不大可能会发生：
If I have time, I will go with them. 假若我有时间，我就同他们去。(陈述语气)
If I were you, I would go with them. 假若我是你，我就同他们去。(虚拟语气)
 
虚拟条件句的三种基本类型
 
一、与现在事实相反
若与现在事实相反，条件从句的谓语用过去式(be通常用were)，主句谓语用“should (would,
could, might)+动词原形”：
If you took a taxi，you’d get there quicker. 如果你坐出租车去，你可以快一点到那里。(但你不坐)
If I knew her number I could ring her up. 要是我知道她的电话号码，我就可以给她打电话了。(可惜我不知道)
 
二、与过去事实相反
若与过去事实相反，条件从句的谓语用过去完成时(had+过去分词)，主句谓语用“should (would, could, might)+have+过去分词”：
If I’d left sooner，I’d have been on time. 要是我早点动身，我就准时到了。(但我动身太迟了)
If we had found him earlier we could have saved his life. 要是我们当时早点到他的话，
我们就可以救活他。(可惜我们到他太晚了)
 
三、与将来事实相反
若与将来事实相反，条件从句的谓语用过去式(be通常用were)，主句谓语用“should (would, could, might)+动词原形”：
If he went，would you go too? 如果他去，你也去吗?(大概他不会去)
If I asked him，I’m sure he’d help us. 如果我向他提出要求，肯定他会帮助我们。(不过我不打算这样做)
注：几点特别说明
① 主句谓语中的should主要用于第一人称后。would, might, could的大致区别是：would表示结果，might表示可能性，could表示能力、允许或可能性。比较：
If you tried again you would succeed. 要是你再试一试，你就会成功的。(would表结果)
If you tried again you might succeed. 要是你再试一试，你可能会成功的。(might表可能)
If you tried again you could succeed. 要是你再试一试，你就能成功了。(could表能力)
② 条件从句的谓语动词为be时，不管其主语为单数还是复数通常都用were，但在口语或非正式文体中的单数第一人称和第三人称后，也可用was，不过在 If I were you这样的表达中，通常还是以用were为宜。
③ 有时条件从句用would表示愿意：
If he would live on with me, I would be his better half. 要是他还愿意跟我过，我仍会做他的妻子。
④ 对于与将来事实相反的情形，请注意以下几点：一是这里说的与将来事实相反，实为对将来情况的推测；二是此用法中的条件从句谓语除用过去式外，有时也用“should+动词原形”(表示可能性极小，常译为“万一”)或“were to+动词原形”(表示与将来事实相反的假设)；三是当条件从句使用“should+动词原形”talk的过去式这样的谓语时，主句谓语除可用“should (would, could, might)+动词原形”这样的虚拟语气外，也可用陈述语气或祈使语气：
If it should rain tomorrow, don’t expect me. 万一明天下雨，就不要等我了。
I should see him, I’ll tell him. 万一我见到他，我就告诉他。
用过去式表示的虚拟语气
 
■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，在第一、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()：
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。
副词long的若干用法限制
 
◆long用作副词时，原则上只用于肯定句和疑问句。如：
—How long will it take to get there?  到那儿需要多长时间?

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