英语四级语法虚拟语气是经常考的内容，所以大家在备考的过程中一定要掌握。下面是小编给大家分享的四级语法知识，大家可以作为学习的参考。

1. if 引导的虚拟语气

a. 指现在的事： 前面用were/过去式，后面用 should (would) +动词原形

例句 If he were here, he would help you now.

b. 指过去的事： 前面用过去完成时，后面用 should (would) have+ 过去分词

例句 If she had worked harder, she would have succeeded.

If he had come yesterday, I should / would have told him about it.

If he had not been ill and missed many classes, he would have made greater progress.

c. 指将来的事： 前面用were/过去式，后面用 should+ 动词原形

或前面用 were+ 不定式，后面用 would + 动词原形

或前面用 should+ 动词原形，后面用 would + 动词原形

例句 If you succeeded, everything would be all right.

If you were to succeed, everything would be all right.

If you should succeed, everything would be all right.

2. 倒装形式

Were I you (=if I were you) , I would get up early in the morning.

Had you arrived at the station ten minutes earlier yesterday(=If you had arrived…), you could have caught the train.

Should it rain (=If it should rain), the crops would be saved.

3、固定句型

“It is (was)+形容词(或过去分词)+that……”结构中的虚拟语气

It is necessary that we (should 可省略,下同)have a walk now.

It was necessary that we (should) make everything ready ahead of time.

4、名词性从句中要用过去时或should+动词原型构成虚拟语气。如：It is time we went home.

5、would rather,had rather后的从句动词用相当于陈述语气的过去时来表示现在或将来发生的动作。

如：I would rather you went with her.我宁愿你跟她走。

只有当would rather后面动作的主体与前面主语一致时才可以用不带 to的动词不定式，

如：I’d rather take the important letter with me.

以上就是小编给大家分享的四级语法知识，希望可以给大家在备考的时候带来帮助。