...may as well ... as ...

结构︰may／might as well＋原形动词 A＋as＋原形动词 B

说明︰此句型意为“与其 B 倒不如 A”。相当于“had better A than B”。“may as well ... as”实现的可能性较大，而“might as well ... as”实现的可能性较小。

Since it is raining hard, you may as well stay here as leave.

既然雨下得这么大，你与其离开倒不如待在这儿。

You might as well throw your money into the sea as lend it to him. 你借他钱不如把钱扔到海里去。

You might as well not know a thing at all as know it only a little. 只知道一点点，不如完全不晓得。

I may as well die as marry him.我与其嫁给他，倒不如去死算了。（我若嫁给他，很可能去死。）

I might as well die as marry him.

我与其嫁给他，倒不如去死算了。（我不太可能嫁给他，也不太可能去死。）

You might as well talk to a stone as try to argue with a stubborn woman.

你与其跟一个倔女人争吵，还不如对一块石头说话。

You might as well advise me to give up my fortune as my argument.

你劝我停止辩论，倒不如劝我抛弃一切财产。

You might as well ask the tree for help as request him to reduce the price.

你与其要他减价还不如求助于一棵树。

... must have V-ed ...

结构︰主词＋must have＋过去分词…

说明︰此句型意为“一定曾经…”。本<句型>是对过去之事做肯定之推测，而“must＋原形<动词>”是对目前或将来之事做推测。

Anyway, he must have eaten a lot because now he is fat.

无论如何，他一定吃了很多东西，因为现在他胖了。

You must have mistaken her for her sister. 你一定是把她误认为是她的姊妹了。

They must have left. 他们一定是离开了。

The rubbing must have worked. 搓揉一定是有效了。

They must have read the article. 他们一定读过这篇文章。

You must have seen him before. 你以前一定见过他。

He must have forgotten my name. 他一定忘了我的名字。

He must have told you about it. 他一定告诉过你这件事。

Tom must have taken your dictionary by mistake. 汤姆一定是弄错了才拿了你的字典。

The poet must have been very young when he wrote this poem.诗人写这首诗时一定非常年轻。

... 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 wouldn’t 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 didn’t 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。