2019英语专四语法考点：情态助动词

2019-03-14 16:28:28来源：网络

　　---Sorry, sir. But it's the management rules of our hotel that payment shall be made in cash.(规章制度)

　　Should (1)表示劝告、建议、命令，其同义词是ought to;在疑问句中，通常用should

　　代替ought to。如：

　　You should go to class right away. Should I open the window?

　　(2) should用于第一人称时可以表示说话人的一种谦逊、客气、委婉的语气。

　　① I should think it would be better to try it again. 我倒是认为最好再试一试。 ② You are mistaken, I should say. 依我看，你是搞错了。

　　(3)Should还可以用在if引导的条件从句，表示一件事听起来可能性很小，但也不是完全没有可能。相当于“万一”的意思。从句谓语由should加动词原形构成，主句谓语却不一定用虚拟语气。如：

　　① If you should change your mind, please let us know. 万一你改变主意，请通知我们。 ② Should I (If I should) be free tomorrow I will come. 万一我明天有时间，我就来。

　　(4)此外，Why(or How) + should结构表示说话人对某事不能理解，感到意外、惊异等意思。意为“竟会”。如：

　　① Why should you be so late today? 你几天怎么来得这么晚? ②— Where is Betty living? — 贝蒂住在哪里? — How should I know? — 我怎么会知道呢?

　　③ I don't know why you should think that I did it. 我真不知道你凭什么认为这事是我干的。

(5). Should 表示推测，按常理，按惯例应该. 如。 They should arrive by 10 o’clock. . “should /ought to+ have done”表示本应该做而实际上没有做，包含一种埋怨、责备的口气。如： She should have finished it. I should have helped her, but I never could.

6) will和would的用法

　　1. 表示请求、建议等，“Will/Would you „.” would比will委婉客气。如： Would you pass me the book?

　　2. 表示意志、愿望和决心。如：

　　I will never do that again. They asked if we would do that again.

　　3. will表示习惯和倾向性。 will表示现在的习惯，would表示过去的习惯，此时的意义接近used to 如：

　　Oil will float on water. 油总是浮在水上。 This window won’t open. 这扇窗户经常打不开。 The wound would not heal. (过去伤口老不愈合。 would与used to的区别：

　　1)used to强调今昔对比(过去这样，现已不是这样);would只是回顾过去,常与often, frequently,sometimes, always, for hours,on Sundays等表频率的词连用。

　　2)would只能表示过去习惯性的动作，而used to 既可表示动作，也可表示状态 4. will表示对目前情况的推测，主要用于第二、三人称。如： This will be the book you want. He will have arrived by now.

7) ought to的用法

　　1. Ought to表示应该。如： You ought to take care of him.

　　2. 表示推测。注意与must表示推测时的区别： He must be at home by now. (断定他已到家) He ought to be home by now. (不十分肯定)

　　3. “ought to + have done”表示过去应做某事而实际未做。如： You ought to have asked him (but you didn't). 这时，ought to和should可以互相换用。

　　8) used to，had better，would rather的用法

　　1. Used to表示过去的习惯动作或状态，现在已不存在，在间接引语中，其形式可不变。如： He told us he used to play football when he was young.

　　在疑问句、否定句、否定疑问句或强调句中，可有两种形式：疑问句 Did you use to go to the same school as your brother? Used you to go to the same school as your brother? 否定句 I usedn't to go there. I didn't use to go there.

　　Usedn't 亦可拼作usen't，但发音皆为[ju:znt]。

　　否定疑问句 Usen't you to be interested in the theatre? Didn't you use to be interested in the theatre? 强调句 I certainly used to smoke, but it was a long time ago. I certainly did use to smoke, but it was a long time ago. 其反意疑问句或简略回答中，也有两种形式：

　　She used to be very fat, didn't she? (正式)/ use(d)n't she? (口语) Did you use to play chess? Yes, I did.

　　Used you to get up early in the morning? Yes, I did. (Yes, I used to.) 2. Had better意为“最好”，后接不带to的不定式。如： — We had better go now.

　　— Yes, we had (we'd better / we had better).

　　Hadn't we better stop now? (Had we better not stop now?)

　　I think I'd better be going. (用于进行时态，表“最好立即”) You had better have done that. (用于完成时态，表未完成动作) 注：①had best与had better同意，但较少用

　　②You had better … 用于同辈或小辈，对长辈不可用。

　　3. Would rather意为“宁愿”，表选择，后接不带to的不定式。如： I'd rather not say anything. Would you rather work on a farm? — Wouldn't you rather stay here? — No, I would not. I'd rather go there. 由于would rather表选择，因而后可接than。如： I would rather work on a farm than in a factory. I'd rather you didn't talk about this to anyone.

9)情态动词+have done(陈述过去)

　　must have done (肯) 定/肯定做过某事 may have done (肯，否) 可能做过某事 might have done (肯，否) 本能够做某事却未做可能做过某事

　　can have done (否，疑问) 可能做过某事 could have done (肯，否，疑问本能够做某事却未做 /

　　可能做过某事

　　should / ought to have done 本应该做某事却未做 needn’t have done 本没必要做某事却做了

　　10)情态动词表推测

　　1 表示肯定的猜测时，各情态动词语气强弱如下：最强——must(一定) will (很有可能) would(很有可能)

　　ought to(应该，很有可能) should(应该，很有可能) can(可能) could(可能) may(可能)

　　最弱——might(可能)

　　2 表示否定的猜测时can't / couldn't语气最强，指“不可能”;may / might not语气最弱，意思是“可能不”。

　　3 一些情态动词表猜测时的用法限制。 must只用于肯定句;

　　may/ might一般不用于疑问句;