完成體是動詞的一種形式，表示動作或狀態已經完成，結構是：主動詞have的不同時態+-ed分詞。可以分為現在完成體和過去完成體。現在完成體大家比較熟悉了，那么今天小編就和大家一起學習我們不太熟悉的過去完成體~

過去完成體，顧名思義，就是表示在過去某一時間之前已經發生或完成的動作，也就是我們所說的“過去的過去”。因此，它有“已完成”用法和“未完成”用法。結構為：had+-ed分詞。

一、“已完成”：表示一個動作或狀態在過去某時之前已經完成或結束。

I had finished my homework when my friends came.我朋友來的時候，我就已經完成家庭作業了。

My father had left for Beijing before I came home. 在我到家前，爸爸已經離開去北京了。

二、“未完成”：表示一個動作或狀態在過去某時之前已經開始，一直延續到這一過去時間，而且到那時還未結束，仍有繼續下去的可能性。

Jack said that he had made much progress in English since he came here.

杰克說自從他到這兒以后，英語已經取得了很大進步。

By six o’clock these workers had worked twelve hours. 到六點鐘時，這些工人已經工作十二小時了。

三、連詞引導過去完成體用法：有些連詞引導的過去完成時可互換。

When I reached the station, the train had already left.

=I reached the station after the train had left.

=I didn’t reach the station until the train had left.

=The train had left before I reached the station.

在我到車站時，火車已經走了。

四、過去完成體的虛擬用法：表示與過去事態相反的主觀設想。

1. 用于if, if only, as if引導的分句：

If you had worked hard, you would have passed the exam. 如果你努力學習的話，你就已經通過考試了。

If I were you, I would not do it. 我要是你，就不做這事。

If only I had finished it before. 要是我之前完成了這件事就好了。

I felt as if I had been a bird in the sky.我感覺自己好似天空一只小鳥。

2. 用于I wish, I would rather引導的that從句：

I wished that I had knew the answer to the question before he asked me. 我希望在他問我以前，我知道問題的答案。

I would rather you had told me the truth. 我寧愿你跟我說實話。

3. 用于expect, think, intend, mean, want, suppose等表示過去未曾實現的希望、打算或意圖。

I had intended to buy a present for you, but I forgot that. 我本打算給你買禮物的，但我忘了。

I had hoped that we could pass the exam, but we failed in the end. 我本希望我們都能通過考試，但最終我們失敗了。

因此，由上可知，比起現在完成體，過去完成體用法復雜，且具體“虛擬”的特殊用法，需要我們在平時使用中加以注意。