高三英语一轮复习情态动词用法小结讲义

情态动词
情态动词表示说话者的某种感情或语气，本身有词义。

一、情态动词的特征
1.情态动词不能独立作谓语，必须同不带to的不定式连用，构成复合谓语。

但have to，ought to，used to除外。

2.情态动词一般没有人称和数的变化。

3.多数情态动词都有现在和过去两种形式，可以表示现在、过去和将来。

二、情态动词的基本用法
1.can，could与be able to表示能力
(1)can表示现在的能力时（即有某种知识和技能而能办到），可与be able to换用，但can
更为常用。

(2)can还表示可能性，常用于疑问句和否定句中。

(3)could泛指过去的能力，一般可与was/were able to通用。

(4)be able to可以表示经过努力在某个场合成功地办成某件具体的事情，相当于succeed in，
而can/could则无此意。

①Tom could sing English songs at the age of 4. (could表过去的能力)
②Tom is able to / can speak English fluently. (can与be able to 表现有的能力）
③After years of hard work he was able to win the prize. (be able to 相当于succeed in)
2.must 与have to
(1)must表示说话人的主观意愿，而have to表示客观需要。

(2)must可以表示“偏偏，执意要”，指不愉快的事，而have to 一般不可以。

①You must decide what approach you want to use.
②She has to do it herself since she has got no one to help her.
3.shall, will和would
(1)shall可与第一人称连用，表示征求意见或请求指示，也可用于第二、三人称，表示允
诺、命令、意志或必然结果等。

(2)will用于一般的经常性、习惯性动作；would用于描述过去的习惯。

①Shall I e in, sir?
②You shall return this book to the library tomorrow.
③ A drowning man will catch at a straw.
ed to 和would
(1)used to强调过去的习惯性动作或状态，但如今已经不存在，与现在的情况形成对比，
即可表示过去持续的状态，也可表示过去重复的行为，意为“过去常常”。

(2)would 用于回想过去，强调过去某种特定情况下的活动，是完全过去的事情，同现在没
有联系。

(3)would表示重复的活动，不表示状态。

①He would/used to get up early in the morning.
②You are no longer what you used to be.
③Man used to think that the Earth was flat. (不能用would)
5.should have done, shouldn’t have done 与needn’t have done
(1)should have done 表示本应该做的事而没有做。

它还可以表示意外、不满或轻微的批评。

(2)shouldn't have done表示某种行为本不该发生但却发生了。

(3)needn't have done 表示一种已经做过的但并无必要的行为。

①She shouldn’t have left the hospital so soon, for she had not yet recovered.
②You needn’t have taken a taxi here, for it is near to your house.
③I should have tried my best to help him when he was in trouble.
6.must have done, may/might have done和can/could have done
(1)must have done 表示对过去行为的推断，具有较大的可能性，意为“一定，必然是”
(2)may/might have done 常用于推测过去的行为，表示“已经可能”。

(3)can/could have done 表示过去能做而没有做的事，或某事可能发生而没有发生。

(4)can/could have done还可以用于推测过去的行为，表示“可能（已发生某事）”，可与过
去时间状语连用。

①Tom is a top student. He must have worked out that question.
②I could have won the race if I hadn’t fallen.
③Peach blossoms may have fallen, but they will bloom again.
练习：
1.If you _______ go, at least wait until the storm stops.
2.You _____ have watered your flower. Or else it wouldn’t be dead.
3.Sometimes she _____ take a walk in the neighboring woods.
4.The weather turned out to be fine yesterday. I needn’t ________(take) the trouble to carry my umbrella with me.
5._________(能够）tell the truth at last seemed to relieved her.
Keys:
1.must
2.should
3.would
4.have taken
5.Being able to。