2018英语专四语言知识高频语法点详解:情态动词

2018-03-14 16:25:21来源:网络

2018英语专四语言知识高频语法点详解:情态动词

2018英语专四语言知识高频语法点详解汇总

  1.情态动词的基本用法

  主要考点包括:

  ·must意为“必须”,而mustn't意为“禁止”。must对应的否定含义“不必”的表现形式有很多种:needn't,don't need to,do not have to等。

  ·need和dare只有在否定句和疑问句中才能作情态动词,且也可以作实义动词;在肯定句中,dare和need则只能作实义动词,后面跟动词不定式。例如:

  You needn't do that.

  You don't need to do that.

  He needs to work10hours every day to support the family.

  2.情态动词表示推测

  ·must和can't表示推测时确定程度最高,但是前者表示对事实的肯定推测,而后者表示对事实的否定推测;may和might表示推测时确定程度均不高,虽然前者比后者要稍高一些,两者既可以表示对事实的肯定推测,也可以表示对事实的否定推测。例如:

  He must be in his room now.

  He can't be in the library now.

  I'm not sure where he is.He may/might be in the library.

  I don't know whether he is there.He may/might not be there.

  ·情态动词加动词原形(一般为be)表示对现在或将来情况的推测,情态动词加动词的进行时表示对现在或将来正在发生事情的推测,情态动词加动词的完成时表示对过去发生事情的推测,情态动词加动词的完成进行时表示对过去正在发生事情的推测。例如:

  He must be Chinese.

  He can't be doing his homework now.He must be watching TV.

  He must have finished his homework.

  He can't have been doing his homework yesterday afternoon.

  3.情态动词与动词完成时连用

  ·may/might/must/can't have done表示对过去发生事情的推测。

  ·should/ought to have done意为“本应该”,表示过去应该做某事而实际上没有做。例如:

  I ought to have known he would do asilly thing like that.

  ·could have done意为“本可以”,表示过去某事可能发生却没有发生。例如:

  I felt so regretful.I could have helped him.

  ·needn't have done意为“本不必”,表示本来没有必要做某事,但是却做了。例如:

  You needn't have finished all that—how kind of you!



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