(一)情態動詞
一.情態動詞的現在完成式的用法
情態動詞現在完成式主要有兩個功能：表示已經發生的情況和表示虛擬語氣。在這兩個方面must/mustn’t,;can/cann’t;need/needn’t;may/mayn’t;might/mightn’t;should/shouldn’t;
ougtht等情態動詞+完成式表示的意思是有一定區別的
1.表示已經發生的情況。
1)must have+過去分詞，表示對已發生情況的肯定推測，譯為“(昨天)一定……”。如：
My pain apparent the moment I walked into the room, for the first man I met asked sympathetically:” Are you feeling all right?”
[A] must be [B] had been [C] must have been [D] had to be
(答案為C)
2)can’t / couldn’t have+過去分詞，表示對已發生情況的否定推測，譯為“(昨天)一定沒……”。如：
Mary my letter; otherwise she would have replied before now.
[A] couldn’t have received [B] ought to have received
[C] has received [D] shouldn’t have received
(答案為A)
3)may / might have +過去分詞，表示對已發生的事情做不肯定、可能性很小的推測，或事實上根本沒發生，譯為“也許……”。如：
At Florida Power’s Crystal River plant, a potentially serious leakage of radioactive water may have been unknowingly caused by an electrician.
2.表示虛擬語氣。
1) needn’t have + 過去分詞，表示做了不必做的事，相當于”didn’t need to do”,譯為“其實沒必要……”。如：
You needn’t have come over yourself.
As it turned out to be a small house party, we so formally.
[A] needn’t dress up [B]did not need have dressed up
[C] did not need dress up [D] needn’t have dressed up
(沒有必要穿的那么正式，體現是說話者的建議，實際結果是否真的穿的很正式沒有確定，答案為D)
2)should have +過去分詞，表示應該做某事但實際上未做，譯為“本應該……”should not + have過去分詞表示本不應該做某事但實際上做了，譯為“本不應該……”。如：
I regret having left the work unfinished; I should have planned everything ahead carefully.
我本來應該事先認真地把每件事情規劃的很好，但實際上作者還是沒有規劃好，以至工作沒有完成。
3) ought to have +過去分詞，表示動作按理該發生了，但實際上未發生，譯為“該……”，與should 的完成式含義類似。如：
The porter ought to have called the fire-brigade as soon as he saw the fire in the stock, which went up in smoke .
4) could have +過去分詞，表示過去本來可以做但卻未做，譯為“完全可以……”。這點與ought/should/ have +過去分詞用法相似。如：
What you said is right, but you could have phrased it more tactfully.
5) may/ might have +過去分詞，表示過去可以做但實際未做，譯為“(那樣)也許會……”。如：
It might have been better to include more punchy statistics and photos of equipment in the introduction to further assist first-time office automation managers.
二.幾個情態動詞常考的句型：
1).may/might (just) as well “不妨，最好”，與had better相近;
Since the flight was cancelled, you might as well go by train.
既然航班已經取消了，你不妨乘火車吧。相當于you had better go by train。
2) .cannot / can’t…too …“越……越好，怎么也不過分”。注意這個句型的變體cannot…over….如：
You cannot be too careful when you drive a car.駕車時候，越小心越好。
The final chapter covers organizational change and development. This subject cannot be over emphasized .
3) .usedn’t 或did’t use to 為used to (do) 的否定式。
4).should 除了“應該”一層意思外，考研大綱還規定要掌握其“竟然”的意思。如：I didn’t expect that he should have behaved like that. 我無法想象他竟然這樣做。
三.情態動詞被動關系的主動表達法
1. want, require, worth(形容詞)后面接doing也可以表示被動意義。
Your hair wants cutting
The book is worth reading
The floor requires washing.
2.need既可以用need to be done 也可以使用need doing ，兩種形式都表達被動的意義
The house needs painting= the house needs to be painted.
The watch needed repairing= the watch needed to be repaired.
