should have done只用于谈论过去情况，主要有两个用法：
■用于推测过去已经发生的情况。如：
He should have arrived by now. 此时他本该到了。
The letter should have arrived by now. 信现在该到了。
The train should have already left. 火车大概已经开走了吧。
I can’t think why he should have been so angry. 我想不通他怎么会这样生气。
■用于指本该发生而实际上未发生的情况。如：
You should have told me so before. 你早就应该告诉我。
Look at the time! We should have been at the theatre ten minutes ago. 瞧都什么时候了! 十分钟前我们就该到戏院了。
George never should have joined the army. 乔治本来就不该参军的。
You should have told me you were coming. 你该事先告诉我你要来呀。
You should have written—I was getting worried. 你该来封信啊——我都开始担心了。
John should have left have left by tomorrow. 到明天约翰可能已走了。
I think they should have consulted a doctor earlier. 我认为他们早就该去看医生了。
I should have left London before 9, but I didn’t. 我本该在9点以前离开伦敦，但是我没有。
In my opinion, she should have resigned earlier. 在我看来，她应当更早一点儿辞职。
You are right; I should have thought of that. 你说得对，我本应当想到这一点的。
I should have phoned Ed this morning, but I forgot. 今天上午我本该给埃德打电话，但是我忘了。
would have done
"would＋动词的完成式"表示对过去的某种情况进行猜测，或本来要做某事却因某种原因未做成，通常用来说明某一情况，但不像用should或ought to那样含有责备之意。
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一、表“猜测过去”
I guess the poet would have been about twenty when she wrote her first poem.
我猜这位诗人写第一首诗歌的时候，大概20岁左右。
Another worker wouldn’t have acted like that.
想必另外一位工人是不会那样做的。
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二、表“过去本会发生，而实际并未发生”，没有责备之意。
I would have written before but I have been ill.
本来我是会写信的，但是由于我生病了。
（用来说明某一情况，没有责备之意）