4. can 和 may

考試中主要測(cè)試can，may或could，might表示可能性的區(qū)別及對(duì)may構(gòu)成的疑問(wèn)句的回答

can, could, may, might都可以表示可能性.can, could表示潛在的可能性或理論上或邏輯判斷上存在的可能性；而may, might則表示事實(shí)上的可能性。此外，can還具有“有能力”的意思，而may與might則不具此意。例如：^

① According to the weather forecast, it may rain tomorrow. 　 據(jù)氣象預(yù)報(bào)，明天可能下雨。

② Any man with a little sense can see that he is wrong. 　 任何一位有頭腦的人都能看出他錯(cuò)了。

May I / we …？這一類(lèi)疑問(wèn)句的肯定回答為Yes, please.或Certainly；否定回答為Please don’t.或No, you mustn’t. 例如：

　 　③ ---May we leave now? 　 　我們可以走了嗎？

---No, you mustn’t. You haven’t finished your home work yet. 　 不行，你們還沒(méi)完成工作呢。

3. would和used to

used to表示過(guò)去與現(xiàn)在或過(guò)去某時(shí)與后來(lái)的情況有不同，而would只表過(guò)去的情況。例如：

① People used to think that the earth was flat.過(guò)去人們認(rèn)為地球是平的。(現(xiàn)在人們不這么認(rèn)為。)

② She would go out for a walk in the morning when she was in the country.

在鄉(xiāng)下時(shí)，她總是在早晨去散會(huì)兒步。(可能現(xiàn)在仍有散步的習(xí)慣。)

used to可表示過(guò)去的習(xí)慣動(dòng)作和經(jīng)常的情況，而would只表示過(guò)去的習(xí)慣動(dòng)作。例如：

① He used to ∕would smoke while writing. 　 過(guò)去他寫(xiě)東西時(shí)常抽煙。

② She used to be fat. 　 她過(guò)去很胖。

2. must和 have to

must 和 have to 都可以表示“必須”，但有幾點(diǎn)區(qū)別：

must 強(qiáng)調(diào)“內(nèi)在的職責(zé)”、“義務(wù)”，而have to 強(qiáng)調(diào)“外界壓力”、“不得已而為之”。^

have to可用于多種時(shí)態(tài)，而must一般用于現(xiàn)在時(shí)，其過(guò)去時(shí)與將來(lái)時(shí)分別由had to與shall / will have to代替。

在回答must引起的問(wèn)題時(shí)，如果是否定的答復(fù)，不能用mustn’t，而要用needn’t或don’t have to，因?yàn)閙ustn’t是“一定不要”、“一定不能”的意思。例如：

① You must come to the classroom before eight. 　八點(diǎn)前你必須來(lái)教室。

② It is raining hard outside, but I have to leave now. 　雖然外面下著大雨，可我還是得走了。

③ ---Must we do it now? 　 　我們必須現(xiàn)在做嗎？

---No, you needn’t. 　 不，不必。

1. can 和be able to

情態(tài)動(dòng)詞can只有兩種時(shí)態(tài)形式，現(xiàn)在式can和過(guò)去式could，而be able to有多種時(shí)態(tài)形式。例如：

① Mary can play the piano. She has been able to play it since she was 5. 　 瑪麗會(huì)彈鋼琴。她五歲起就會(huì)彈了。

用在過(guò)去時(shí)中，could經(jīng)常表示能夠做某事，事實(shí)上不一定去做，而was / were able to則表示“過(guò)去做成了某事”。在否定句中兩者可通用。例如：

② He could swim across the English Channel. But he didn’t feel like it that day. 　他能游過(guò)英吉利海峽，但那天他不想游。

③ Yesterday I was able to get home before the heavy rain. 　 昨天我在下大雨前趕到了家里。

3. would和used to

1)used to表示過(guò)去與現(xiàn)在或過(guò)去某時(shí)與后來(lái)的情況有不同，而would只表過(guò)去的情況。

People used to think that the earth was flat.

過(guò)去人們認(rèn)為地球是平的。(現(xiàn)在人們不這么認(rèn)為。)

She would go out for a walk in the morning when she was in the country.

在鄉(xiāng)下時(shí)，她總是在早晨去散會(huì)兒步。(可能現(xiàn)在仍有散步的習(xí)慣。)

2)used to可表示過(guò)去的習(xí)慣動(dòng)作和經(jīng)常的情況，而would只表示過(guò)去的習(xí)慣動(dòng)作。

He used to ∕would smoke while writing. 　 過(guò)去他寫(xiě)東西時(shí)常抽煙。

She used to be fat. 　 她過(guò)去很胖。

◆ 考題剖析

例題1. I didn't hear the phone. I ________ asleep. (NMET 89)

A. must be 　 　 B. must have been 　 　 　 C. should be 　 　 D. should have been;

答案 B 　從原題中的I didn't hear the phone．這一信息可以判斷出，用must have

done表示對(duì)過(guò)去事實(shí)的準(zhǔn)確的肯定猜測(cè)。

例題2. Tom ought not to 　 　 　 　 　 　 me your secret ,but he meant no harm. (NMET93)

　 　 　 　 　 A. have told 　 　 B. tell 　 　 　C. be telling 　 　 　D. having told

答案 A 　 該句意思是：“湯姆本來(lái)不該告訴我你的秘密，但他沒(méi)有傷害你的意思。”

例題3. I was really anxious about you. you 　 　home without a word. (NMET2001)

A. mustn't leave 　 　 　 　 　 　 B. shouldn't have left

C. couldn't have left 　 　 　 　D. needn't leave.

答案 B 　shouldn't have done為不該做了某事。

例題4. ---Could I borrow your umbrella, please?

　 　 　 　---I’m afraid you _______.

　 　 　 A. could 　 　 　 　 B. can 　 　 　C. couldn’t 　 　 　 　D. can’t

答案 D 　此題極易錯(cuò)選C。其實(shí)could在問(wèn)句中表示請(qǐng)求，為了語(yǔ)氣的委婉和客氣才用過(guò)去式，而答句必須按照實(shí)際情況回答，故選can’t，以求和I’m afraid(在此表示婉拒)一致。

例題5. ---Don't forget to come to my birthday party tomorrow.

　 　 　 　---______.`

　A. I don't　 B.　I won't　 C. I can't　D. I haven't

答案 B　 will既可當(dāng)作情態(tài)動(dòng)詞，表請(qǐng)求、建議、也可作為實(shí)義動(dòng)詞表"意愿、意志、決心"，本題表示決心，故選B。

例題6. ----Shall we go skating or stay at home?

----Which ___ do?

A. do you rather　B. would you rather　　 C. will you rather　 D. should you rather

答案 B 　 本題考查情態(tài)動(dòng)詞would rather的用法，would rather +do sth 意為“寧愿”，本題為疑問(wèn)句，would 提前，所以選B。

◆思考

幾組情態(tài)動(dòng)詞的辨異

2. must和 have to語(yǔ)法學(xué)習(xí)綱要由江蘇省靖江高級(jí)中學(xué)外語(yǔ)組為英語(yǔ)貓網(wǎng)站特供

must表示主觀意志，而have to表示由于客觀因素不得不做某事。must沒(méi)有過(guò)去式，除在間接引語(yǔ)中可用于表示過(guò)去時(shí)間，在直接引語(yǔ)中表示過(guò)去時(shí)間應(yīng)該用had to代替。

I told her that she must give up smoking. 　我叫她必須戒煙。

We had to get everything ready that night. 　我們那晚得把一切準(zhǔn)備就緒。"

1. can 和be able to

1)情態(tài)動(dòng)詞can只有兩種時(shí)態(tài)形式，現(xiàn)在式can和過(guò)去式could，而be able to有多種時(shí)態(tài)形式

Mary can play the piano. She has been able to play it since she was 5. 　

瑪麗會(huì)彈鋼琴。她五歲起就會(huì)彈了。

2)用在過(guò)去時(shí)中，could經(jīng)常表示能夠做某事，事實(shí)上不一定去做，而was / were able to則表示“過(guò)去做成了某事”。在否定句中兩者可通用。

He could swim across the English Channel. But he didn’t feel like it that day.

他能游過(guò)英吉利海峽，但那天他不想游。

Yesterday I was able to get home before the heavy rain. 　 昨天我在下大雨前趕到了家里。

1. 情態(tài)動(dòng)詞后跟完成式和進(jìn)行式的用法

1) 情態(tài)動(dòng)詞+動(dòng)詞完成式

情態(tài)動(dòng)詞+動(dòng)詞完成式即“情態(tài)動(dòng)詞+ have + done分詞”，表示對(duì)過(guò)去行為或動(dòng)作進(jìn)行推測(cè)、評(píng)論或判斷。

must have done 表示對(duì)過(guò)去某事的肯定猜測(cè)。其否定或疑問(wèn)形式都用can(could) 來(lái)表示。 　例如： 　

① Since the road is wet, it must have rained last night.

② He can’t have missed the way. I drew him a map.

③ The dictionary has disappeared. Who could have taken it?

當(dāng)然對(duì)現(xiàn)在發(fā)生或?qū)��?lái)發(fā)生的事情,要用must do 表示猜測(cè), 否定為can’t do。例如：

④ He must understand that we mean business.

⑤ You must be hungry after a long walk.

may / might have done表示推測(cè)過(guò)去某事“也許”發(fā)生了.may 比 might 表示的可能性在說(shuō)話(huà)人看來(lái)稍大些。例如：

⑥ I can’t find my keys. I may / might have left them at the school yesterday.

could have done 在肯定句型中, 往往用作委婉的批評(píng). 本應(yīng)該做什么,而沒(méi)做; 有時(shí)也用作猜測(cè)。例如：

⑦ You could have told us earlier.

⑧ Tom could have taken the dictionary.

ought to / should have done和 ought not to / shouldn’t have done用于對(duì)已發(fā)生的情況表示“責(zé)備”、“不滿(mǎn)”，分別表示“本應(yīng)該…”和“本不應(yīng)該…”。例如：

⑨ With all the work finished, I should have gone to the party last night.

⑩ You ought not to have made fun of him. He is not the one you laugh at but learn from.

needn’t have done 表示過(guò)去做了某事，但沒(méi)有做的必要， 意為“本沒(méi)必要…”。例如：

⑾ You needn’t have waken me up; I don’t have to go to work today.

[注意]表示推測(cè)過(guò)去某動(dòng)作發(fā)生的可能性時(shí)，就表示的可能性程度而言，must最大，could其次，may更次之，might最小。例如：

　 　 ⑿ ---I wonder how Tom knew about your past. 　

---He must / could / may / might have heard of it from Mary.

2) 情態(tài)動(dòng)詞+動(dòng)詞進(jìn)行式

情態(tài)動(dòng)詞+行為動(dòng)詞進(jìn)行式(即情態(tài)動(dòng)詞+ be + doing形式)，表示推測(cè)或評(píng)論某動(dòng)作現(xiàn)在是否正在進(jìn)行。例如：

① He must be playing basketball in the room.

② She may be staying at home.

3) 情態(tài)動(dòng)詞+動(dòng)詞完成進(jìn)行式

情態(tài)動(dòng)詞+行為動(dòng)詞完成進(jìn)行式(即情態(tài)動(dòng)詞+ have been + v-ing形式)，表示推測(cè)或評(píng)論過(guò)去某動(dòng)作是否正在進(jìn)行或一直在進(jìn)行。例如：

① They should have been meeting to discuss the problem.

② He may / might have been buying stamps in the post office when you saw him.|

9.特殊情態(tài)動(dòng)詞need和dare的用法：

need和dare既可用作情態(tài)動(dòng)詞，也可用作實(shí)義動(dòng)詞。用作情態(tài)動(dòng)詞時(shí)，主要用于否定句和疑問(wèn)句。用作實(shí)義動(dòng)詞時(shí)，可用于各種句式。

1) 用作情態(tài)動(dòng)詞。例如：|

① You needn’t telephone him now. 　 你現(xiàn)在不必打電話(huà)給他。

② I don’t think you need worry. 　 我想你不必發(fā)愁。

③ She dare not go out alone at night. 　 她晚上不敢一個(gè)人出去。

④ How dare you say I’m unfair? 　 你竟敢說(shuō)我不公平？_

2) 用作實(shí)義動(dòng)詞。例如：

① You don’t need to do it yourself. 　 你不必親自做這件事。

② We need to tell them the news. 　 我們需要把這消息告訴他們。

③ The table needs painting (to be painted.). 　 桌子需要油漆一下。

④ We should dare to give our own opinion. 　 我們要敢于提出自己的觀點(diǎn)。

⑤ He did not dare (to) look up. 　 他不敢抬頭看。

⑥ I dare say he’ll come again. 　 我想他會(huì)再來(lái)的。

[注意](I dare say…為固定習(xí)語(yǔ))

◆ 難點(diǎn)突破

8. used to

表示過(guò)去的習(xí)慣動(dòng)作或狀態(tài)，現(xiàn)在不復(fù)發(fā)生或存在。疑問(wèn)式和否定式有兩種。例如：i

① There used to be a building at the street corner, but it has been pulled down. 　 街道拐角處過(guò)去有座樓房，現(xiàn)在拆了。

② I usedn’t (didn’t use) to smoke. 　 我過(guò)去不抽煙。j }F

③ Used you (Did you use) to go to school on foot? 你過(guò)去常步行去學(xué)校嗎？