情態動詞復習
5 must表示推測
1) must用在肯定句中表示較有把握的推測，意為"一定"。
2) must表對現在的狀態或現在正發生的事情的推測時， must 后面通常接系動詞be 的原形或行為動詞的進行式。
you have worked hard all day.you must be tired. 你辛苦干一整天，一定累了。（對現在情況的推測判斷）
he must be working in his office. 他一定在辦公室工作呢。
比較：
he must be staying there.
他現在肯定呆在那里。
he must stay there.
他必須呆在那。
3) must 表示對已發生的事情的推測時，must 要接完成式。
i didn't hear the phone. i must have been asleep. 我剛才沒有聽到電話，我想必是睡著了。
4) must表示對過去某時正發生的事情的推測，must 后面要接不定式的完成進行式。
---why didn't you answer my phone call?
---well, i must have been sleeping, so i didn't hear it.
5) 否定推測用 can't。
if tom didn't leave here until five o'clock, he can't be home yet. 如果湯姆五點才離開這兒，他此時一定還未到家。
6 表示推測的用法
can, could, may, might, must 皆可表示推測，其用法如下：
1）情態動詞+動詞原形。
表示對現在或將來的情況的推測，此時動詞通常為系動詞。
i don't know where she is, she may be in wuhan.
2）情態動詞+動詞現在進行時。
表示對現在或將來正在進行的情況進行推測。
at this moment, our teacher must be correcting our exam papers.
這時，我們老師想必在批改試卷。
3）情態動詞+動詞完成時。
表示對過去情況的推測。
we would have finished this work by the end of next december.
明年十二月底前我們很可能已完成這項工作了。
the road is wet. it must have rained last night.
地是濕的，昨天晚上一定下雨了。
4）情態動詞+動詞的現在完成進行時。
表示對過去正在發生事情的推測。
your mother must have been looking for you.
你媽媽一定一直在找你。
5）推測的否定形式，疑問形式用can't, couldn't表示。
mike can't have found his car, for he came to work by bus this morning.
邁克一定還沒有找回他的車，因為早上他是坐公共汽車來上班的。
注意：could, might表示推測時不表示時態，其推測的程度不如 can, may。
7 情態動詞+ have +過去分詞
1) may(might) have + done sth, can (could) have + done sth 表示過去，推測過去時間里可能發生的事情。
philip may (might) have been hurt seriously in the car accident.
philip can (could) have been hurt seriously in the car accident.
2) must have +done sth，對過去時間里可能發生的事情的推測，語氣較強，具有"肯定"，"諒必"的意思。
--- linda has gone to work, but her bicycle is still here.
---she must have gone by bus.
3) ought to have done sth, should have done sth
本應該做某事，而事實上并沒有做。否定句表示"不該做某事而做了"。