情态动词与虚拟语气用法详解
一． 情态动词
主要特征：1）不能单独作谓语，只能和行为动词或系动词连用，构成谓语；
2）没有人称和数的变化，时态也只限于一般现在时和一般过去
3）后面接动词原形，即不带to的不定式；
二．情态动词的基本用法
1.must
（1）“必须，一定，得”，表示的是命令性的语气。
Eg.You must hand in your composition today.
*回答must引起的一般疑问句，如果是否定意思，常用needn't。
Eg.-Must I come at four o'clock?？
-Oh, no, you needn't come at four.。
*用mustn't 则表示“禁止”。
Eg.Cars mustn't park in front of the entrance.
（2）there you will be表示“偏要，硬要”做某事。表示与说话人的意愿相反和不耐烦的语气
Eg.As I was about to start to work, the telephone must ring.
must 与have tostir区分：must更强调说话者的主观意愿；have to则强调客观上的必要性，常译为“不得不”，而have to可以有多种时态变化。
2.can
（1）表示能力。Eg.I can swim across the river when I was young.
（2）表示客观（理论）上的可能性，用于肯定句中。
Eg.Anybody can make mistakes.
（3）表示请求和允许，怀疑多用于否定与疑问结构中：
Eg.-Can I go now? -Yes, you can.
Can the news be true?
重点短语：1)cannot but do sth. 表示“不得不，只好”
Eg.I cannot but choo to go with them.
2)cannot/ ugh/too表示“再......也不为过”：
Eg.You cannot be too careful to cross the road.
3)can not help but do, can not help doing 表示“不得不”“禁不住”：
Eg.The girl couldn't help but live on herlf.
3.may
（1）表示可能，意为“或许，也许”
Eg.She may come to your birthday party tomorrow.
weles（2）表示允许、许可。否定回答时，一般要用mustn't，表示“禁止，阻止”：
Eg.-May I watch TV after supper?
-Yes, you may. / No, you mustn't.
（3）可以用于祈使句，表示祝愿：May we never forget each other.
may/ might as well do sth. “最好，满可以，倒不如”：
Eg.It's too late. You might as well not go.
4.dare 既可作情态动词，又可作实义动词。情态动词dare多用于否定句、疑问句以及条件句，过去式为dared。 实义动词dare to do
I dare say为固定短语，表示“我认为，我相信”
Eg.My sister daren't go out when night falls.
Eg.Do you dare to drive a car on such a crowded road?
5.need既可作情态动词，又可作实义动词。情态动词need多用于否定句、疑问句以及条件句，其肯定回答用must，否定回答用needn't。
need作实义动词时，注意：need to do：需要做某事，主动
need doing= need to be done需要被做，被动
6.shall
（1）用于第一、三人称的疑问句中表示说话人征求对方意见和向对方请示；
Shall I nd you the book?
（高帽子2）用于第二、三人称的陈述句，表示说话人给对方的命令、警告、允诺或威胁等。
You shall fail if you don't work hard.
（3）should表示“应该；假使；万一；竟然”
You shouldn't drink and drive.
注意Why/ How should表示说话人对某事不能理解、感到意外、等意为“竟会”。
Eg.Why should you be so late today?
（4） ought to 表示职责和义务，常译作“应该”
否定形式：ought not to/ oughtn't to
一般疑问句形式：将ought置于主语前
Ought I to make an apology to Joan?
7.will, would
（1）表示征求对方(第二人称)意见或询问对方意愿 would 比will 更客气委婉
Eg.Will you have some more wine?
Eg.Would you mind my smoking here?
（2）will 表示习惯性动作或某种倾向 would 表示过去习惯性动作或某种倾向
Eg.Fish will die out of water.
subjectiveEg.When I was young, I would play badminton on Sundays.
（3） will 表示意愿 决心
Eg.I will never do that again.
三．常见的表示推测的情态动词用法比较
情态动词 | 适用形式 | 适用时态 | 意义 | 语气轻重 |
must | 只用于肯定句 | must +dobecome的过去分词 must+be doing must+have done | 一定，肯定 | 语气最重 |
can/ could | 在职研究生报名常用于疑问句和否定句 | cann’t/couldn’t+do cann’t /couldn’t+be doing cann’t /couldn’t +have done | 可能，能够 | 语气次之 |
may/ might | 可用于肯定句、否定句和疑问句 | may/ might +do may/ might +be doing may/ might +have done | 也许，可能 | 语气最轻 |
| | | | |
3. “情态动词+have done”的用法
构成 | 用法 | 举例 |
must + have done | 表示对过去发生的事情十分肯定的推测。must表示推测时，不能用于否定句和疑问句。 | The man must have stayed up. 。 |
should/ ought to + have done | 用于肯定句，表示 “本来应该......的（但实际上却没有......）”，含有责备的意思；用于否定句意思为“本来不该......的（但实际上却已经......了）”。 | Perhaps we should have taken the other road. It might have been quicker. You shouldn't/ ought not to have let him do that; he might have got lost. |
may/ might + have done | 成绩查询用于肯定句和否定句，表示对过去发生某事的可能性推测，意思为“或许（已经）......” | He said that she might have misd the plane. |
cann’t / couldn’t + have done | 多用于否定句和疑问句，表示对过去某事发生的t推测，意思为“不可能（已经）......了 | He can't / couldn't have en her there. |
could+have done | 用于肯定句，表示本能做某事却没做 | You could have helped him. |
| 韩语发音 needn't + have done | 表示对过去已经做了某事而后悔，意思为“本来可以不必......的（可实际上却已经......了）”。 | We needn't have worried. 我们本不必担心。 |
| | |
虚拟语气
语气：是动词的一种形式，表示说话人对发生的动作或所处的状态持有的态度.
英语中有三种语气：陈述语气（陈述事实） 祈使语气（祈使句中）
虚拟语气：表示说话人的假设，猜测，而不是客观存在的事实。
注意：虚拟语气的be无论主语是第几人称均为were
一． If 型虚拟（非真实条件句中的虚拟语气）
If条件句可分为两类：真实条件句,非真实条件句
非真实条件句表示的是假设的或实际可能性不大的情况，故要用虚拟语气。
情况 | if从句谓语 | 主句谓语 | 例句 |
与现在事实相反 | did | would/could/ should/ might + do | If I were you, I would follow his advice. |
与过去事实相反 | had + done | would/could/ should/might+ have done | If we had driven in turn, you wouldn't have got so tired. 。 |
与将来事实相反 | did sunt是什么意思should + do were to + do | would/could/ might/ should + do | If it snowed/ were to snow/should snow tomorrow, We would take photos. |
| | | |
三种特殊情况
1）倒装的条件句：若条件句中有were, had, should时，可把if省略，而把were, had, should提到主语前，形成倒装的条件句。
Eg.If I were you, I would take this job.
Were I you, I would take this job.
注意：如果倒装的条件句的谓语动词是否定形式时，不能用动词的缩略形式。
( × ) Weren't it for the expen, I would go abroad now.
