一、情态动词表推测的三种句式
1.在肯定句中一般用must (一定),can,could(可能),might /may(也许,或许)。
(1)He must/can/may,might know the answer to this question.
他一定/可能/也许知道这个问题的答案。
(2)It is cold in the room. They must have turned off the heating.
屋里很冷,他们肯定把暖气关了。
2.否定句中用can’t / couldn’t(不可能),may not/might not(可能不)。
(1)It can’t/couldn’t be the headmaster. He has gone to America.
这不可能是校长,他去美国了。
(2)He may not/might not know the scientist.
他也许不认识那位科学家。
3.疑问句中用can/could (能……?)。
(1)Could he have finished the task?
他可能把任务完成了吗?
(2)Can he be at home now?
他现在能在家吗?
注:以上三种句式中情态动词的语气按程度都是依次递减的。Might,could并非may,can的过去式,而表示语气较为委婉或可能性较小。
二、情态动词表推测的三种时态
1.对将来情况的推测,用“情态动词 + 动词原形”。
(1)She must / may / might / could arrive before 5.
5:00前她一定/可能/也许到。
(2)She must/may/might/could walk miles and miles among the hills without meeting anyone.
她一定/可能/也许会在山里一连走好几英里而遇不到一个人。
2.对现在或一般情况的推测,用“情态动词 + be”,“情态动词 +be doing”或“情态动词 + 动词原形”。
(1)He must / may / might / could be listening to the radio now.
他一定/可能/也许正在听收音机。
(2)He can’t ( couldn’t ) / may ( might ) not be at home at this time.
这个时候他不可能/可能不在家。
(3)Mr. Bush is on time for everything .How can ( could ) he be late for the opening ceremony
布什先生一向准时,这次开幕式他怎么可能迟到呢?
3.对过去情况的推测,用“情态动词 + have +过去分词”。
(1)It must / may / might / could have rained last night .The ground is wet.
地湿了,昨晚肯定/可能/也许下雨了。
(2)The door was locked. He can ( could ) not / may ( might ) not have been at home .
门锁着,他不可能/可能不在家。
(3)Can / Could he have gotten the book?
难道他找到书了吗?
注:情态动词 should /ought to表推测时,意为“想必会,理应……”但与“have +过去分词”连用时,则又可构成虚拟语气意为“本应该做某事却没做”。例如:
(4)It’s seven o’clock. Jack should/ought to be here at any moment.
现在七点钟了,杰克理应随时到达。(推测)
(5)She should / ought to have attended your birthday party,but she had to look after her mother in hospital. (虚拟)
她本该出席你的生日晚会的,可是她得在医院照顾她妈妈。
(6)Tom should not /ought not to have told me your secret,but he meant no harm. (虚拟)
汤姆本不该告诉我你的秘密,可是他并无恶意。