專升本英語語法基本知識（情態(tài)動詞）

此前，為大家推送過專升本英語語法基本知識狀語從句的內(nèi)容，今天為大家?guī)砹饲閼B(tài)動詞的部分，希望對大家有所幫助。

情態(tài)動詞有can, could, may, might, must, should, ought to, need, dare, had better, would rather 等。情態(tài)動詞相當于助動詞，不能單獨使用，必須再接動詞原型。

1. can, could表示能力、允許、客觀可能性。

注意:表能力時could是can的過去式；表允許時could比can更委婉，表客觀可能性時could 可能性比can 小。

eg:She is only four, but she can read.

This sort of thing can't go on.

I couldn't follow her speech.

Could you lend me your bike?

Fire can't destroy gold. 真金不怕火練

2. may, might表示允許、猜測。

[注意]表允許時might比may更委婉;表客觀可能性時might可能性比may小。

eg:The dialect of one province may be quite different from that of the next one.

Students may not stay out after midnight without written permission. (stay out在外邊待的很晚)

He asked his mother if he might go out to play.

"May I open the window?" "Yes, please./ Please don't./ No, you mustn't." (mustn't “不許、不準”)

3. must

1)表示可能性"肯定"、"準是"，其否定形式是can't

2)表示"必須"。must只用在一般現(xiàn)在時和一般將來時，此時must= have/has to,而have to可以用在任何時態(tài)。其否定形式needn't

3)mustn't表示"千萬不要"、"一定不要"。

eg:He must be a student.

Teachers always tell us we must do everything step by step.

--Must I go tomorrow?

--No, you needn't.(Yes, I'm afraid so. must一般疑問句的否定用needn't來回答)

He has to/must tidy up the room everyday. (tidy up打掃干凈)

You mustn't talk like that to your parents.

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