... must have V-ed ...
結構︰主詞＋must have＋過去分詞…
說明︰此句型意為“一定曾經…”。本<句型>是對過去之事做肯定之推測，而“must＋原形<動詞>”是對目前或將來之事做推測。
Anyway, he must have eaten a lot because now he is fat.
無論如何，他一定吃了很多東西，因為現在他胖了。
You must have mistaken her for her sister.
你一定是把她誤認為是她的姊妹了。
They must have left.
他們一定是離開了。
The rubbing must have worked.
搓揉一定是有效了。
They must have read the article.
他們一定讀過這篇文章。
You must have seen him before.
你以前一定見過他。
He must have forgotten my name.
他一定忘了我的名字。
He must have told you about it.
他一定告訴過你這件事。
Tom must have taken your dictionary by mistake.
湯姆一定是弄錯了才拿了你的字典。
The poet must have been very young when he wrote this poem.
詩人寫這首詩時一定非常年輕。
... may have V-ed ...
結構︰主詞＋may／might have＋過去分詞
說明︰此句型意為“很可能曾經…”。表示對過去之事做不太肯定的推測。而“may／might＋原形<動詞>”是對現在或未來事物做推測。might have 所表示的可能性要比 may have 低一些。
He may have overslept this morning.
今天早上他或許睡過頭了。
The tea is hot; he may have been here before.
茶還熱著，不久前他很可能在這里。
He may have known the truth; otherwise he wouldn’t be so angry now.
他當時很可能知道事情的真相，否則他不會這么生氣。
The boy might have known the truth, but I am not quite sure.
這男孩當時也許知道真相，但我不很確定。
... cannot have V-ed ...
結構︰主詞＋cannot have＋過去分詞
說明︰此句型意為“不可能曾經…”。是對過去之事做否定的推論，此時一定要用 cannot have 或 cannot，不能使用 must not have 或 must not。而“cannot＋原形<動詞>”是對目前或將來之事做否定的推論。
She cannot have written the letter herself.
這封信不可能是她自己寫的。
He is honest, so he cannot have stolen my money.
他是個老實人，所以他不可能偷了我的錢。
He cannot have caught a cold, because I saw him dancing with Mary the same day.
他不可能感冒，因為當天我還看到他跟瑪麗跳舞。
... would have V-ed ...
結構︰主詞＋would have＋過去分詞
說明︰此句型意為“原本會…但卻未如此”。用以表示“與過去事實相反”的<假設語氣>。
He would have attended meeting, but upon learning that he had no time, he dropped the idea.
他原本要出席會議的，但知道沒有時間，就打消了這個念頭。
I would have told you the truth, but you didn’t give me a chance.
我本來要告訴你事情的真相，但是你不給我機會。
I would have done it, but I had no time.我本來要辦這事的，可是沒時間。
She would have married him, but when she learned that he was a rascal, she parted with him.
她本來會嫁給他的，但知道他是個流氓后，她就離開他了。
... could have V-ed ...
結構︰主詞＋could have＋過去分詞
說明︰此句型意為“原本能夠…但卻未如此”。
He could have bought the car, but soon his company went bankrupt.
他本來能買那輛車的，但沒多久他的公司就倒閉了。
He could have finished it on schedule, but somehow he fell behind.
他原本能按預定進度做完這件事的，但不知怎地卻落后了。
I could have done it if I had wanted to.
如果我那時想做，我能做得到的。
... should have V-ed ...
結構︰主詞＋should／ought to have＋過去分詞
說明︰此句型意為“原本應當…但卻未如此”。此<句型>表示沒有實現之過去的行為、狀態，含有講話者的責難或遺憾之意。
You should have spoken up in the meeting.
會談時你實在應該發言（然而你卻沒有）。
He should at least have come to say good-by.
他至少也該來道個別（然而卻沒來）。
He ought to have kept his promise.
他原本應該遵守自己的諾言。
You should have been more careful in money matters.
在錢方面，你本當更小心點的。
He ought to have arrived there by now.
他現在應該已經到那里了。
The drama drew a capacity audience; you should have gone to see it.
這出戲吸引了滿場觀眾；你真該去看的。
I should have known better
結構︰主詞＋should have known better（than to＋原形動詞）
說明︰此句型意為“本來不應該那樣笨（而…）”，是指已經做過之事，而 know better（不致那樣笨）是指未做之事。
I should have known better.
我本來不應該那樣笨。
You should have known better than to talk like that.
你本應更懂事而不致說這樣的話。
You should have known better than to go mountain climbing alone.
你本來不該笨得單獨去爬山。
I know better than to go swimming after dinner.
我不致笨得吃過飯就去游泳。
... need not have V-ed ...
結構︰主詞＋need not have＋過去分詞
說明︰此句型意為“原本不必…但卻…”。表示“與過去事實相反”的<假設語氣>，即做了沒有必要做的事。而“didn’t need to＋原形<動詞>”則表示“過去的事實”，譯為“當時不必…而且也沒…”。need not have 在<疑問句>中表對過去之必要性的強烈疑問，即“有…的必要嗎？”。
You need not have bought extra oil for this short trip.
在這么短的旅程中，你實在沒有必要多買油。
You need not have got up so early.
你不必起得那么早。
Need he have gone to the station to meet her?
他有必要到車站去接她嗎？
He need not have come. (But he came.)
當時他不必來。（但卻來了）
He didn’t need to come. (And he didn’t come.)
當時他不必來。（而且也沒來）
It was fine that day, so I need not have brought an umbrella with me.
那天天氣很好，我原本不必帶傘的（但卻帶了）。
