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）。
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.