英语四级、英语六级常考语法：虚拟语气
1. 表示现在/过去/将来情况的虚拟条件句
虚拟条件句主要有三种结构：
1）表示与现在情况相反：主句谓语用“would / could / might +动词原形”，从句谓语用“动词的一般过去时”（动词be的过去式一律用were）。
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If I were you， I would not accept his offer.
If I had time， I would certainly go to the cinema with you.
2） 表示与过去情况相反：主句谓语用“would / could / might + have +过去分词”，从句谓语用过去完成时。
If I had got up a little earlier， I wouldn’t have missed the train.
If I had been more careful， I might have passed that exam.
3） 表示与将来情况相反：主句谓语用“would / could / might +动词原形”，从句谓语用“were +动词不定式”或“should +动词原形”。
If I were to do the job， I would not be able to have enough time to study.
If it should rain tomorrow， I would not go out with you.
2. 虚拟条件句连接词if的省略
如果虚拟条件句的从句中含有were， had， should， could等词时，可以省略连接词if，但这时必须把were， had， should， could等词移到主语前面，形成倒装。这种句型主要用于书面形式。
Were I to do the job， I would finish doing it within two weeks.
Had it not been for his help， we couldn’t have arrived there on time.
Should it rain tomorrow， I would stay at home.
3. wish后宾语从句中的谓语构成
动词wish后的宾语从句表示未实现的或不可能实现的愿望，其宾语从句中的谓语动词要用虚拟语气，有以下三种构成形式。
1） 表示现在不可能实现的愿望，宾语从句中的谓语动词用一般过去时。（be的过去式为were）。
I wish I had enough money to buy a car.
I wish I were as young and energetic as you.
2） 表示过去未能实现的愿望，宾语从句中的谓语动词用过去完成时（had +过去分词）或“would / could + have +过去分词 ”。
I wish I hadn’t made such a mistake.
I wish I could have done it better.
3） 表示将来不可能实现的愿望，宾语从句中的谓语动词用“would / should （could， might） +动词原形”。
I wish I would not get old.
I wish I could travel around the world one day.
4. 某些动词后的宾语从句中谓语动词要用虚拟语气
在一些动词后面的宾语从句中，谓语动词要用虚拟语气。这时，谓语动词用动词原形或should +动词原形。这类动词一般表示命令，要求，决定，建议，主张等概念，主要有：advise， ask， command， decide， demand， desire， direct， insist， move， order， propose， recommend， request， require， suggest，等。
The workers demanded that t