may have V-ed
结构︰主词＋may／might have＋过去分词
说明︰此句型意为很可能曾经。表示对过去之事做不太肯定的推测。而may／might＋原形动词是对现在或未来事物做推测。might have 所表示的可能性要比 may have 低一些。
He may have overslept this morning. 今天早上他或许睡过头了。
The tea is hot； he may have been here before. 茶还热着，不久前他很可能在这里。
He may have known the truth； otherwise he wouldnt be so angry now.
他当时很可能知道事情的真相，否则他不会这么生气。
The boy might have known the truth， but I am not quite sure.
这男孩当时也许知道真相，但我不很确定。
cannot have V-ed
结构︰主词＋cannot have＋过去分词
说明︰此句型意为不可能曾经。是对过去之事做否定的推论，此时一定要用 cannot have 或 cannot，不能使用 must not have 或 must not.而cannot＋原形动词是对目前或将来之事做否定的推论。
She cannot have written the letter herself. 这封信不可能是她自己写的。
He is honest， so he cannot have stolen my money.他是个老实人，所以他不可能偷了我的钱。
He cannot have caught a cold， because I saw him dancing with Mary the same day.
他不可能感冒，因为当天我还看到他跟玛丽跳舞。
would have V-ed
结构︰主词＋would have＋过去分词
说明︰此句型意为原本会但却未如此。用以表示与过去事实相反的假设语气.
He would have attended meeting， but upon learning that he had no time， he dropped the idea.
他原本要出席会议的，但知道没有时间，就打消了这个念头。
I would have told you the truth， but you didnt give me a chance.
我本来要告诉你事情的真相，但是你不给我机会。
I would have done it， but I had no time. 我本来要办这事的，可是没时间。
She would have married him， but when she learned that he was a rascal， she parted with him.
她本来会嫁给他的，但知道他是个流氓后，她就离开他了。
could have V-ed
结构︰主词＋could have＋过去分词
说明︰此句型意为原本能够但却未如此。
He could have bought the car， but soon his company went bankrupt.
他本来能买那辆车的，但没多久他的公司就倒闭了。
He could have finished it on schedule， but somehow he fell behind.
他原本能按预定进度做完这件事的，但不知怎地却落后了。
I could have done it if I had wanted to. 如果我那时想做，我能做得到的。
should have V-ed
结构︰主词＋should／ought to have＋过去分词
说明︰此句型意为原本应当但却未如此。此句型表示没有实现之过去的行为、状态，含有讲话者的责难或遗憾之意。
You should have spoken up in the meeting. 会谈时你实在应该发言（然而你却没有）。
He should at least have come to say good-by. 他至少也该来道个别（然而却没来）。
He ought to have kept his promise. 他原本应该遵守自己的诺言。
You should have been more careful in money matters. 在钱方面，你本当更小心点的。
He ought to have arrived there by now. 他现在应该已经到那里了。
The drama drew a capacity audience； you should have gone to see it.
这出戏吸引了满场观众；你真该去看的。
结构︰主词＋may／might have＋过去分词
说明︰此句型意为很可能曾经。表示对过去之事做不太肯定的推测。而may／might＋原形动词是对现在或未来事物做推测。might have 所表示的可能性要比 may have 低一些。
He may have overslept this morning. 今天早上他或许睡过头了。
The tea is hot； he may have been here before. 茶还热着，不久前他很可能在这里。
He may have known the truth； otherwise he wouldnt be so angry now.
他当时很可能知道事情的真相，否则他不会这么生气。
The boy might have known the truth， but I am not quite sure.
这男孩当时也许知道真相，但我不很确定。
cannot have V-ed
结构︰主词＋cannot have＋过去分词
说明︰此句型意为不可能曾经。是对过去之事做否定的推论，此时一定要用 cannot have 或 cannot，不能使用 must not have 或 must not.而cannot＋原形动词是对目前或将来之事做否定的推论。
She cannot have written the letter herself. 这封信不可能是她自己写的。
He is honest， so he cannot have stolen my money.他是个老实人，所以他不可能偷了我的钱。
He cannot have caught a cold， because I saw him dancing with Mary the same day.
他不可能感冒，因为当天我还看到他跟玛丽跳舞。
would have V-ed
结构︰主词＋would have＋过去分词
说明︰此句型意为原本会但却未如此。用以表示与过去事实相反的假设语气.
He would have attended meeting， but upon learning that he had no time， he dropped the idea.
他原本要出席会议的，但知道没有时间，就打消了这个念头。
I would have told you the truth， but you didnt give me a chance.
我本来要告诉你事情的真相，但是你不给我机会。
I would have done it， but I had no time. 我本来要办这事的，可是没时间。
She would have married him， but when she learned that he was a rascal， she parted with him.
她本来会嫁给他的，但知道他是个流氓后，她就离开他了。
could have V-ed
结构︰主词＋could have＋过去分词
说明︰此句型意为原本能够但却未如此。
He could have bought the car， but soon his company went bankrupt.
他本来能买那辆车的，但没多久他的公司就倒闭了。
He could have finished it on schedule， but somehow he fell behind.
他原本能按预定进度做完这件事的，但不知怎地却落后了。
I could have done it if I had wanted to. 如果我那时想做，我能做得到的。
should have V-ed
结构︰主词＋should／ought to have＋过去分词
说明︰此句型意为原本应当但却未如此。此句型表示没有实现之过去的行为、状态，含有讲话者的责难或遗憾之意。
You should have spoken up in the meeting. 会谈时你实在应该发言（然而你却没有）。
He should at least have come to say good-by. 他至少也该来道个别（然而却没来）。
He ought to have kept his promise. 他原本应该遵守自己的诺言。
You should have been more careful in money matters. 在钱方面，你本当更小心点的。
He ought to have arrived there by now. 他现在应该已经到那里了。
The drama drew a capacity audience； you should have gone to see it.
这出戏吸引了满场观众；你真该去看的。
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