情態(tài)動(dòng)詞的用法
情態(tài)動(dòng)詞的用法
情態(tài)動(dòng)詞有can (could), may (might), must, have to, shall (should, will (would), dare (dared), need (needed), ought to等。 情態(tài)動(dòng)詞無人稱和數(shù)的變化;不能單獨(dú)使用，必須與其后的動(dòng)詞原形構(gòu)成謂語。
一、 can, could
1) 表示請(qǐng)求和允許。
-----Can I go now?
----- Yes, you can. / No, you can’t.
此時(shí)可與may互換。在疑問句中還可用could,might代替，不是過去式，只是語氣更委婉，不能用于肯定句和答語中。
---- Could I come to see you tomorrow?
---- Yes, you can. ( No, I’m afraid not. )
2) 表示能力(體力、知識(shí)、技能)。
Can you lift this heavy box?(體力)
Mary can speak three languages.(知識(shí))
Can you skate?(技能)
此時(shí)可用be able to代替。Can只有一般現(xiàn)在時(shí)和一般過去式;而be able to則有更多的時(shí)態(tài)。
I’ll not be able to come this afternoon.
當(dāng)表示“經(jīng)過努力才得以做成功某事”時(shí)應(yīng)用be able to，不能用Can。如：
He was able to go to the party yesterday evening in spite of the heavy rain.
3) 表示客觀可能性(客觀原因形成的能力)。
They’ve changed the timetable, so we can go by bus instead.
This hall can hold 500 people at least.
4) 表示推測(cè)(驚訝、懷疑、不相信的態(tài)度)，用于疑問句、否定句和感嘆句中。
Can this be true?
This can’t be done by him.
How can this be true?
二、 may, might
1) 表示請(qǐng)求和允許。might比 may語氣更委婉，而不是過去式。否定回答時(shí)可用can’t或mustn’t，表示“不可以，禁止”。
----Might/ May I smoke in this room?
---- No, you mustn’t.
---- May/Might I take this book out of the room?
---- Yes, you can. (No, you can’t / mustn’t. )
用May I...?征徇對(duì)方許可時(shí)比較正式和客氣，而用Can I...?在口語中更常見。
2)用于祈使句，表示祝愿。
May you succeed!
3) 表示推測(cè)、可能性(不用于疑問句)。
might不是過去式，它所表示的可能性比may小。
1.He may /might be very busy now.
2.Your mother may /might not know the truth.
三、 must, have to
1) 表示必須、必要。
You must come in time.
在回答引出的問句時(shí)，如果是否定的，不能用mustn’t(禁止，不準(zhǔn))，而用needn’t, don’t have to(不必).
---- Must we hand in our exercise books today?
---- Yes, you must.
---- No, you don’t have to / you needn’t.
2) must是說話人的主觀看法， 而have to則強(qiáng)調(diào)客觀需要。Must只有一般現(xiàn)在時(shí)， have to 有更多的時(shí)態(tài)形式。
1. he play isn’t interesting, I really must go now.
2. I had to work when I was your age.
3) 表示推測(cè)、可能性(只用于肯定的陳述句)
1. You’re Tom’s good friend, so you must know what he likes best.
2. Your mother must be waiting for you now.
四、 dare, need
1) dare作情態(tài)動(dòng)詞用時(shí), 常用于疑問句、否定句和條件從句中, 過去式形式為dared。
1. How dare you say I’m unfair?
2. He daren’t speak English before such a crowd, dare he?
3. If we dared not go there that day， we couldn’t get the beautiful flowers.
2) need 作情態(tài)動(dòng)詞用時(shí), 常用于疑問句、否定句。在肯定句中一般用must, have to, ought to, should代替。
1.You needn’t come so early.
2. ---- Need I finish the work today?
---- Yes, you must. / No, you needn’t.
3) dare和 need作實(shí)義動(dòng)詞用時(shí)， 有人稱、時(shí)態(tài)和數(shù)的變化。在肯定句中，dare后面常接帶to的不定式。在疑問句和否定句中，dare后面可接帶to或不帶to的不定式。而need后面只能接帶to的不定式。
1. I dare to swim across this river.
2. He doesn’t dare (to) answer.
3. He needs to finish his homework today.