2. 表示對過去情況的主觀推測

指對可能已經發生的情況作主觀猜測，其意為“大概已經”，“應該已經”。例如：

The letter should have arrived by now. 信函現在該到達了。

I wonder why he should have been so angry. 我想不通他怎么會這樣生氣。

該用法中的should也可換成ought to，意思不變。例如：

The train should (ought to) have already left. 火車大概已經開走了吧。

但是，我認為，should表推測時僅限于使用肯定形式，不能用否定形式。否則，就不是推測。這一點跟must表推測的用法是一致的，must一旦使用了否定形式，就不表示推測。

You should have no problem with reading this language.讀這種語言你應該沒問題。

The doctor says it will take six weeks and I should be fine by then. 醫生說需要6周時間，到那時我就會好了。

3. 表示驚訝

對已經發生的情況表示驚訝或不理解，通常含有“竟然”的意味。例如：

It is a pity that he should have failed in the exam. 他考試竟然沒有及格，真是可惜。

I can’t think why he should have said that it was my fault. 我真不明白，他怎么竟然說這是我的過錯。

It’s strange that he should have left without telling us. 奇怪，他竟沒有和我們說一聲就走了。

4. 用于虛擬語氣

在虛擬條件句中，當談論過去的情況時，其句型通常是：主句用“could/would/should /might +have+過去分詞”，if從句用過去完成時。虛擬語氣的“should+have+過去分詞”結構，僅限于使用第一人稱。例如：

If I had seen her I should have invited her. 我當時要是看到她的話我本會邀請她的。

If I had received the present, I should have thanked her. 如果我收到了禮物，我是應當向她道謝的。

I should not have laughed if I had thought you were serious. 如果我想到你是認真的，我就不會笑了。

五、needn't have done的用法

needn't have done表示過去沒有必要做某事，意為“本來不必做某事”（但實際做了）。

I needn't have taken the umbrella, for the weather is fine.天這么好，我本沒必要帶雨傘的。

You needn't have told her again.I have told her already.你當時沒必要再告訴她了。我已經告訴過她了。

I needn’t have gone to the office yesterday. 昨天我沒必要去辦公室。

“need +完成時”僅限于否定句或疑問句，不用于肯定句。又如：

I was the first to get there. I needn’t have gone there so early. 我是第一個到那兒的人，我本來不必去那么早的。

You needn’t have mentioned it. 你沒有必要提及此事的。

You needn’t have come in person. 你當時不必親自來的。

Need you have scolded him so severely? 你有必要這樣嚴厲地批評他嗎?

Need he have paid so much? 他當時真需付那么多錢嗎?

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