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四、情態動詞
1. 情態動詞的推測表達
2. 情態動詞表達虛擬語氣
3. 某些情態動詞的特殊用法
知識重點與難點總結
知識重點：
情態動詞在表達推測意義的句子中的運用：
(一)用情態動詞表達事實的推測。can，could，might，may，must可以用來表達對事實的推測。根據說話人對事實的把握性大小，must表示“肯定…”，may / might / can / could表示“可能……”， must只用于肯定句中，may / might的否定式may not / might not表示 “可能不……”, 而can / could可以用于疑問句，表示“可能，可能……嗎?”，其否定式can’t / couldn’t 表示“不可能”。用情態動詞可以對現在或過去的事實進行推測。對不同的時間內容推測有不同的結構。
(二)對現在的事實進行推測：
主要結構：…must / may / might +動詞原形
be+名詞/形容詞/介詞短語
be + doing
例句：
1. You must be Jeanne. I’m Mathilde Loisel. We used to know each other very well.
2. They must be in bed already at this time of the night.
3. The teacher must be joking.
4. Freda isn’t in class. She must be sick.
5. There must be something wrong.
6. She might be very clever, but she hasn’t got much common sense.
7. He may be arriving this evening.
8. He may be traveling around the world.
9. The keys can’t be in the room. I have just searched it very carefully.
10. Can the news be true ?
(三)對過去的事實進行推測：結構：情態動詞+have done / been+名詞/形容詞/介詞短語
例句：
1. Mrs. Longmans must have been a pretty girl in her youth.
2. He couldn’t have seen Anna yesterday. She’s gone abroad.
3. I think I must have left my glasses in the library.
4. He might have overslept again.
5. Where can Tom have gone ?
情態動詞表達虛擬語氣：表達“本來…”，“不然早就…”。這是情態動詞的一種虛擬語氣用法。表示說話人所講的與所發生的事實相反。表達了說話人的埋怨，后悔的語氣。其結構是在一些情態動詞后面加 have done 結構。根據要表達的意思，有如下結構：
should have done / ought to have done：本應該……
shouldn’t have done / oughtn’t to have done：本不該……
could have done：本來可以……
needn’t have done：本來沒必要……
would like to have done：本來很想……
would rather not have done: 本來不愿意……
could / might / have done: 不然早就……
例句：
1. You shouldn’t have laughed at his mistakes.
2. You could have told us earlier.
3. I ought to have bought that dictionary last week.
4. You ought not to have spent so much time in reading novels.
5. We need not have been in a tearing hurry to catch the train.
6. They would like to have seen that film last film.
7. If he had given me his number, I could have telephoned him.
8. They might have been frozen to death but for the rescue in time.