情态动词与动词的时态和语态
情态动词又称为情态助动词。英语中助动词主要有两类：一是基本助动词，如have, do, be等；二是情态助动词，如may, must, need等。情态动词与其他动词连用表示说话人的语气，可表达建议、要求、可能、意愿等。情态动词没有人称和数的变化。
一、情态动词+动词完成式
情态动词must, should, may(might), ought to, can(could), need, would等都可以与动词完成式连用作谓语，其模式为 modal verb+have+v-ed 。这类结构表示对过去所发生动作的推测或判断。但是，不同的情态动词所表示的意思又有所不同。
1、must+have+v-ed和can t/couldn t+have+v-ed
must+have+v-ed 表示对过去事情较有把握的、肯定性的推测，常译为 一定 ， 准是 ， 肯定 。当must用于推测意义时，其否定形式通常不是must not, 而是can/could not. can t/couldn t+have+v-ed 表示对过去事情的否定性推测，常译为 决不可能 ， 不太可能 。
例：Since the ditch is full of water, it must have rained last night.
经典练习：
1、Mary s score on the test is the highest in her class; she____have studied very hard.
A)may
B)should
C)must
D)ought to
2、You____her in her office last Friday; she s been out of town for two weeks.
A)needn t have seen
B)must have seen
C)might have seen
D)can t have seen
3、Mary____my letter; otherwise she would have replied before now.
A)has received
B)ought to have received
C)couldn t have received
D)shouldn t have received
4、Dinosaurs are thought to____millions of years ago
A)die out
B)have died out
C)having died out
D)dying out点击下一页查看答案
