情态动词(二)
内 容 提 要
情态动词有can(能)，may(可以)，must(必须)，have to(不得不)，ought to(应该)，dare(敢)，used to(过去经常)，had better(最好)，would rather(宁愿)。在肯定句中它们后边都要接 动词原形 .在否定句中，can，may，must和dare后边加not;have to和ought to分别在have和ought后加not;used to的否定式可用used not to，也可用didn't use to，但后者用得较多;had better和would rather的否定式分别是had better not和would rather not.这些情态动词与现在完成时连用在某种意义上有一定的虚拟性。
情态动词与完成时的使用
一、must+have+ED分词：用于肯定句，表示对过去情况的一种肯定推测，表示“肯定，一定”
1) It around nine o'clock when I drove back home because it was already dark.
[A] had to be [B] must have been [C] was to be [D] must be
2) John's score on the test is the highest in the class;
[A] he should study last night
[B] he should have studied last night
[C] he must have studied last night
[D] he must had to study last night
3) After searching [A] for evidence in the house，the police concluded [B] that the thief must have come in [C] through the window and stole [D] the silver while the family was asleep.
二、may (might)+have+ED分词：用于肯定句和否定句，表示对已发生事情的不肯定的推测，相当于“可能，大概，”其中might较may 语气更弱，把握更小
She might have gone to see her doctor last week， but I am not sure.
上星期或许她去看医生了，但我不敢肯定。
Don't worry， your husband may not have been hurt seriously.
别急，你丈夫也许伤得不厉害。
三、should(ought to)+have+ED分词：肯定句表示过去本应发生的事却没有发生;否定句表示已发生了本不该发生的事。前者可译为“本应，”后者为“本不该”
You should have apologized to her for not soon replying to the letter. 你本应向她道歉，说明为什么没能及时回信。(可你没这么做)
4) You yesterday if you were really serious about your work.
[A] ought to come[B] ought to be coming[C] ought to have come[D] ought have come
四、can(not) +have+ED分词
He is an hour late —— He can have been delayed by fog. Of course，that's a possibility.他迟到了1小时，可能因为大雾而耽搁了。当然这只是可能性问题。
The poem can not have been written by her since she was only five years old then.这诗不可能是她写的，因为她那时才5岁。
五、“could+have+ED分词”有时用于表示过去的时间，说明某事可能或不可能已发生;有时可表示过去本来可以做某事，但却未做
I simply can't understand how he could have made such a mistake. 我简直不明白他怎么会犯那样的错误。
H
