(2) 對(duì)過(guò)去的推測(cè)，必須在 can, could 之后接動(dòng)詞的完成式。但此時(shí)can仍只用于否定句或疑問(wèn)句，不用于肯定句；而could則可用于各種句型：

He can’t [couldn’t] have seen her there. 他不可能在那兒見(jiàn)到她。

He could have gone home. 他可能已回家了。

Who could have taken it? 是誰(shuí)把它拿走了呢?

I do not see how I could have done otherwise. 我看不出那時(shí)我還能有別的做法。

She could not have been more than sixteen. 那時(shí)她不可能超過(guò)十六歲。

I couldn’t have won, so I didn’t go in for the race. 我不可能獲勝，因此我沒(méi)參賽。

【注】could后接動(dòng)詞的完成式，除表示對(duì)過(guò)去的推測(cè)外，還有以下用法(不用can)：

① 表示過(guò)去沒(méi)有實(shí)現(xiàn)的可能性(即某事本來(lái)可以發(fā)生，卻沒(méi)發(fā)生)：

He could have told her, but he didn’t choose to. 他本來(lái)可以告訴她的，但他卻沒(méi)有。

I could have lent you the money. Why didn’t you ask me? 我本來(lái)可以借這筆錢給你的。你為什么不問(wèn)我?

② 用來(lái)委婉地責(zé)備某人過(guò)去應(yīng)該做某事而沒(méi)有去做：

You could have been a little more considerate. 你本可考慮得更周到些的。

You could ask me before you use my phone. 你打電話之前可以問(wèn)我一聲。

You could have helped me why did you just sit and watch? 你本可幫助我的，為什么只坐在一旁瞧著?

③ 表示“差點(diǎn)兒就要”：

I could have died laughing. 我差點(diǎn)笑死了。

I was so angry I could have killed him. 我是那樣生氣，差點(diǎn)把他殺了。

She felt miserable. She could have cried. 她感到很痛苦，她差點(diǎn)哭了。

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