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情態動詞的用法大全(2)
2) must是說話人的主觀看法， 而have to則強調客觀需要。Must只有一般現在時， have to 有更多的時態形式。1. he play isn’t interesting, I really must go now.
2. I had to work when I was your age.
3) 表示推測、可能性(只用于肯定的陳述句)
1. You’re Tom’s good friend, so you must know what he likes best.
2. Your mother must be waiting for you now.
四、 dare, need
1) dare作情態動詞用時, 常用于疑問句、否定句和條件從句中, 過去式形式為dared。
1. How dare you say I’m unfair?
2. He daren’t speak English before such a crowd, dare he?
3. If we dared not go there that day， we couldn’t get the beautiful flowers.
2) need 作情態動詞用時, 常用于疑問句、否定句。在肯定句中一般用must, have to, ought to, should代替。
1.You needn’t come so early.
2. ---- Need I finish the work today?
---- Yes, you must. / No, you needn’t.
3) dare和 need作實義動詞用時， 有人稱、時態和數的變化。在肯定句中，dare后面常接帶to的不定式。在疑問句和否定句中，dare后面可接帶to或不帶to的不定式。而need后面只能接帶to的不定式。
1. I dare to swim across this river.
2. He doesn’t dare (to) answer.
3. He needs to finish his homework today.
五、 shall, should
1) shall 用于第一人稱，征求對方的意見。
What shall we do this evening?
2) shall 用于第二、三人稱，表示說話人給對方的命令、警告、允諾或威脅。
1. You shall fail if you don’t work hard.(警告)
2. He shall have the book when I finish it.(允諾)
3. He shall be punished.(威脅)
六、 will, would
1) 表示請求、建議等，would更委婉。
Will / Would you pass me the ball, please?
2) 表示意志、愿望和決心。
1. I will never do that again.
2. They asked him if he would go abroad.
3) would表示過去反復發生的動作或某種傾向。would表示過去習慣時比used to正式，且沒有“現已無此習慣”的含義。
1. During the vacation, he would visit me every other day.
2. The wound would not heal.
4) 表示估計和猜想。
It would be about ten o’clock when she left home.
七、 should, ought to
1) should, ought to表示“應該”，ought to表示義務或責任，比should語氣重。
1. I should help her because she is in trouble.
2. You ought to take care of the baby.
2) 表示勸告、建議和命令。should, ought to可通用，但在疑問句中常用should。
1. You should / ought to go to class right away.
2. Should I open the window?
3) 表示推測
should , ought to (客觀推測), must(主觀推測)。
1.He must be home by now. (斷定他已到家)
2.He ought to/should be home by now.(不太肯定)
3. This is where the oil must be.(直爽)
4. This is where the oil ought to/should be.(含蓄)
八、 情態動詞+不定式完成式(have done)
1) can / could + have done在肯定句中表示“本來可以做而實際上能做某事”，是虛擬語氣;在疑問句或否定句中表示對過去行為的懷疑或不肯定, 表示推測。
1. You could have done better, but you didn’t try your best. (虛擬語氣)
2. He can’t have been to that town.(推測)
3. Can he have got the book?(推測)
2) may / might +不定式完成式(have done)
表示對過去行為的推測。不能用于疑問句中，沒有虛擬語氣的用法。Might所表示的可能性比may小。
1. He may not have finished the work .
2. If we had taken the other road, we might have arrived earlier.
3)must +不定式完成式(have done)
用于肯定句中，表示對過去行為的推測。意為“一定、想必”。其疑問、否定形式用can，can’t代替。參看1) can / could + have done表示推測。
1. You must have seen the film Titanic.
2. He must have been to Shanghai.
4)should +不定式完成式(have done)
用于肯定句中，表示對過去行為的推測。
He should have finished the work by now。
表示“本應該做而實際上沒有做某事”，其否定式表示某種行為本不該發生卻發生了。可以與ought to +不定式完成式(have done)互換。
1. You ought to / should have helped him. (but you didn’t.)
2. She shouldn’t have taken away my measuring tape, for I wanted to use it.
5) needn’t +不定式完成式(have done)
表示“本來不必做而實際上做了某事”。
You needn’t have watered the flowers, for it is going to rain.
6) will +不定式完成式(have done)
主要用于第二、三人稱，表示對已完成的動作或事態的推測。
He will have arrived by now.
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