If I had known that,I could have helped you.had和known怎么都是过去式,have在这里是什么意思,为什么它不用过去式

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IfIhadknownthat,Icouldhavehelpedyou.had和known怎么都是过去式,have在这里是什么意思,为什么它不用过去式IfIhadknownthat,Icouldhav

If I had known that,I could have helped you.had和known怎么都是过去式,have在这里是什么意思,为什么它不用过去式
If I had known that,I could have helped you.had和known怎么都是过去式,have在这里是什么意思,为什么它不用过去式

If I had known that,I could have helped you.had和known怎么都是过去式,have在这里是什么意思,为什么它不用过去式
这是虚拟语气,表示与事实相反的情况.
had known是过去完成时,have是助动词,是现在完成时的标志.
这一句表示与过去的事实相反.

known 不是过去式,而是过去分词.用于现在完成时.have+动词是现在完成时的形式.
had是过去式可能是因为联系上文.
have不用过去式是因为前面有could这个情态动词,情态动词后面要加动词原形

Subjunctive mood,不知道的话别着急，以后会学的。
它（这个判断）是假的，不可能发生的，所以要用虚拟的方法变一下。这是虚拟语气那一堆的一部分。
本来应该说have known，把现在时变成过去时，完成态不变，所以是过去完成。
其实我也不太清楚，等高中再学吧。...

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Subjunctive mood,不知道的话别着急，以后会学的。
它（这个判断）是假的，不可能发生的，所以要用虚拟的方法变一下。这是虚拟语气那一堆的一部分。
本来应该说have known，把现在时变成过去时，完成态不变，所以是过去完成。
其实我也不太清楚，等高中再学吧。

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在过去不同时间发生的两个动作中,发生在先,用过去完成时;发生在后,用一般过去时。
主语＋had+过去时

如果我知道我一定会帮助你的（此句隐含的意思就是我当时不知道所以没有帮助你）
虚拟语气（对事情的假设）
对已经发生过的事情假设就用过去完成时had done
如果帮助了那也已经是发生过的事情了（虽然没有帮助），所以也是过去完成时，但由于前面有could所以就原型了...

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如果我知道我一定会帮助你的（此句隐含的意思就是我当时不知道所以没有帮助你）
虚拟语气（对事情的假设）
对已经发生过的事情假设就用过去完成时had done
如果帮助了那也已经是发生过的事情了（虽然没有帮助），所以也是过去完成时，但由于前面有could所以就原型了

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