一、用法歸納

1. 表示推測的情態(tài)動詞有must, can, could, may, might等，且語氣由左向右依次減弱。could, might并不一定是can, may的過去式，有時只是語氣分別比can, may更弱。

2. must (一定會，準(zhǔn)會) 只用于肯定句；can (可能)一般用于疑問句或否定句；may (也許) 用于肯定句或否定句。雖然must和may均可用于肯定句，但在語氣上must比may強得多，must表示有把握的肯定推測，而may表示沒有把握的肯定推測。雖然can和may均可用于否定句，但在語氣上can’t(不可能)比may not(可能不)要強得多，can’t是表示有把握的否定推測，而may not是表示沒有把握的否定推測。could, might可用于肯定句、否定句或疑問句中，其區(qū)別在于語氣上強弱的區(qū)分。

3. should, ought to (按理應(yīng)當(dāng)), would, will,(很可能)等也可表示推測，語氣都較肯定，且由左至右依次增強，但較must稍弱。

4. 關(guān)于表示推測的情態(tài)動詞后面所接動詞形式，有下列三種情況：若對此刻正在發(fā)生的事，接“be +現(xiàn)在分詞”；若對現(xiàn)在或未來情況的推測，接動詞原形；若對過去情況的推測，接“have +過去分詞”。

?

二、實例分析

◎—Excuse me. Is this the right way to the Summer Palace?

—Sorry, I am not sure. It ________ be. (湖北卷)

A. might??????????????????????? B. will

C. must???????????????????????? D. can

【分析】答案選A。由I am not sure(我沒有把握)可知，后文是沒有把握的肯定推測，用might。

◎You might just as well tell the manufacturer that male customers ________ not like the design of the furniture. (上海卷)??

A. must????????????????????????? B. shall

C. may?????????????????????????? D. need

【分析】答案選C。. may not意為“可能不”。句意是：你不妨告訴廠商男顧客可能不喜歡這種家具的花樣。

◎—Isn’t that Ann’s husband over there?

—No, it ________ be him—I’m sure he doesn’t wear glasses. (全國卷)

A. can’t????????????????????????? B. must not

C. won’t???????????????????????? D. may not

【分析】答案選A。由No和后文I’m sure…可知，是有把握的否定推測，所以用can’t (不可能)。

◎—When can I come for the photos? I need them tomorrow afternoon.

—They ________ be ready by 12:00. (全國卷)

A. can???????????????????????????? B. should

C. might????????????????????????? D. need

【分析】答案選B。should表示“按理應(yīng)當(dāng)，大概”。用might語氣太不肯定，顧客可能走掉。

◎I have lost one of my gloves. I ________ somewhere. (北京春)

A. must drop?????????????????????? B. must have dropped???????????

C. must be dropping???????????? D. must have been dropped

【分析】答案選B。對已經(jīng)發(fā)生的事進行推測用“must have +過去分詞”，答案D是被動式，應(yīng)排除。

◎—I stayed at a hotel while in New York.

—Oh, did you? You ________ with Barbara. (全國卷)

A. could have stayed????????????? B. could stay

C. would stay??????????????????????? D. must have stayed

【分析】答案選A。表示對過去情況的推測：“你可能和Barbara住在一起了”；must語氣太肯定，與前面具有疑問語氣的Oh, did you?不符。

◎—There were already five people in the car but they managed to take me as well.

—It ________ a comfortable journey. (全國卷)

A. can’t be??????????????????????????? B. shouldn’t be

C. mustn’t have been????????????? D. couldn’t have been

【分析】答案選D。既然小汽車上“已有五人”，且是“設(shè)法”才把你帶去的，如此擁擠，旅途當(dāng)然“不可能”舒服。

◎—Tom graduated from college at a very young age.

—Oh, he ________ have been a very smart boy then. (全國III)

A. could??????????????????????????????? B. should

C. might??????????????????????????????? D. must

【分析】答案選D。由上文可知，應(yīng)是有把握的肯定推測，用must(一定)。

◎You ________ be tired—you’ve only been working for an hour. (四川卷)

A. must not?????????????????????????? B. won’t

C. can’t??????????????????????????????? D. may not

【分析】答案選C。由后文“你才只工作了一個小時”推斷，“你不可能就累了”。表示有把握的否定推測，用can’t。must not不允許；may not可能不。

◎It’s nearly seven o’clock. Jack ________ be here at any moment. (全國卷)

A. must??????????????????????????????? B. need

C. should????????????????????????????? D. can

【分析】答案選C。nearly暗示“時間不早了”，“按理應(yīng)當(dāng)(should)”Jack“隨時(at any moment)”都有可能到達這里。must又語氣過強；can一般不用于肯定推測；need意義不通，也不用于肯定句。

◎I didn’t hear the phone. I ________ asleep. (全國卷)

A. must be???????????????????????????? B. must have been

C. should be?????????????????????????? D. should have been

【分析】答案選B。當(dāng)時我沒不聽到電話鈴響，那“一定是己經(jīng)睡著了。

◎—Is John coming by train?

—He should, but he ________ not. He likes driving his car. (全國卷)

A. must???????????????????????????????? B. can

C. need???????????????????????????????? D. may

【分析】答案選D。由“他自己喜歡開車”這一習(xí)慣推斷，“他可能不會(may not)坐火車來”。can not“不可能”，語氣太肯定。

◎Peter ________ come with us tonight, but he isn’t very sure yet. (全國卷)

A. must??????????????????????????????? B. can

C. may???????????????????????????????? D. will

【分析】答案選C。由but he isn’t very sure. (但他沒有把握)可知，Peter晚上來的可能性是不大的。表示沒有把握的肯定推測用may(也許)。

◎—Are you coming to Jeff’s party?

—I’m not sure. I ________ go to the concert instead. (全國卷)

A. must?????????????????????????????? B. would

C. should???????????????????????????? D. might

【分析】答案選D。由I’m not sure可知，“我可能(might)要去聽音樂會”

◎Michael ________ be a policeman, for he’s much too short. (上海卷)

A. needn’t??????????????????????????? B. can’t

C. should???????????????????????????? D. may

【分析】答案選B。由he’s too short推知，Michael“不可能(can’t)”是 policeman。

?