... 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 wouldnt 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。

　　... 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 wouldnt 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。