Step 1 Introduction

1)What's the function of the underlined words?

We are having an English class.

帮助主要动词have构成现在进行时

I have seen the film.

帮助主要动词see构成现在完成时

He didn't go home last night.

帮助主要动词go构成一般过去时

We will fly for Africa next month.

帮助主要动词fly构成一般将来

He was sent to England.

帮助主要动词send构成被动语态

I would fly to Sweden if I were a bird.

帮助主要动词构成虚拟语气

Had I lived in London, I would have been to London Bridge. 帮助主要动词构成虚拟语气

Tip：助动词和其他动词一起构成时态、语气和语态。可以用作助动词的有be、do、have和情态动词。

2)We have/need to go home now. 表示必要性

Students must study hard. 表示职责

It can be very hot in summer in our hometown.

表示可能性

TIP：情态动词表示必要性、职责和可能性。像其他助 动词一样，情态动词也用于其他主要动词前，不能单独做句子的谓语。因此，情态动词也被当作情态助动词。

3)Do you like college life?

Did you study English before you came here?

I do not like him.

Do call me tomorrow.

He did know that.

Tip:助动词还可用来构成否定或疑问句，以及强调结构

补充：do用作代动词

e.g.: - Do you like Beijing?

- Yes, I do.

（do用作代动词，代替like Beijing.）

4)短语助动词由一个助动词和另一个或两个词组成.如：have (got) to, had better, would sooner/rather(...than), be to, be likely to, be supposed to, ought to, used to, be about to ,be able to, etc.

e.g.:

I have (got) to clean the blackboard before the teacher comes.

I have (got) to go now; my wife will be waiting for me.

You didn't have to tell her the whole story.

Tip: have (got) to 表示"得做某事"，或提出建议，其否定形式not have to意为"不必"。

Many countries would rather be cautious with this new technology.

I would sooner walk to work than take a bus.

Tip: would rather/sooner(...than)的意思是"宁愿,更愿意"。

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