、过去完成时的概念与结构特点
概念：过去完成时表示在过去某一时间或动作之前已经发生或完成了的动作，即“过去的过去
（past-i n-the-past ）”。
----| -------------------------
I ---------------------------- 1 -------------------------- >
那时以前 那时 现在
构成：过去完成时由“助动词 had + 过去分词”构成，其中 had 通用于各种人称。
They had already had breakfast before they arrived at the hotel.
She had finished writing the composition by 10 : 00 this morning.
二、过去完成时的判断依据
1. 由时间状语来判定
一般说来，各种时态都有特定的时间状语。与过去完成时连用的时间状语有：
（1 ） by + 过去的时间点。
如: I had finished reading the novel by nine o'clock last night.
（2 ） by the end of + 过去的时间点。
女口： We had lear ned over two thousa nd En glish words by the end of last term.
（3 ） before + 过去的时间点。
女口： They had pla nted six hun dred trees before last Wedn esday.
2. 由“过去的过去”来判定。
过去完成时表示“过去的过去”，是指过去某一动作之前已经发生或完成的动作，即动作有先后关系， 动作在前的用过去完成时，在后的用一般过去时。这种用法常出现在：
（1 ）宾语从句中
当宾语从句的主句为一般过去时， 且从句的动作先于主句的动作时， 从句要用过去完成时。 在told, kn ew, heard, thought 等动词后的宾语从句。如：
She said that she had see n the film before.
（2 ）状语从句中
过去完成时
said,
在时间、条件、原因、方式等状语从句中，主、从句的动作发生有先后关系，动作在前的，要用过去完成时，动作在后的要用一般过去时。如：
When I got to the station, the train had already left.
After he had finished his homework, he went to bed.
注意：before, after 引导的时间状语从句中，由于before 和after 本身已表达了动作的先后关系，
若主、从句表示的动作紧密相连，则主、从句都用一般过去时。如：
Where did you study before you came here?
After he closed the door, he left the classroom.
（3 ）表示意向的动词，如hope, wish, expect, think, intend, mean, suppose 等，用过去完成时表示
"原本…，未能…"
We had hoped that you would come, but you didn't.
3. 根据上、下文来判定。
I met Wang Tao in the street yesterday. We hadn't seen each other since he went to Beijing.
三、过去完成时的主要用法
1. 过去完成时表示一个动作或状态在过去某一时间或动作之前已经完成或结束，即发生在“过去的过去” 。如：When I woke
up, it had stopped raining.
我醒来时，雨已经停了。（主句的动作发生在“过去的过去” ）
2. 过去完成时是一个相对的时态，表示的是“过去的过去” ，只有和过去某一时间或某一动作相比较时才使用它。如：
He told me that he had written a new book. （had written 发生在told 之前）
3. 过去完成时需要与一个表示过去的时间状语连用，它不能离开过去时间而独立存在。此时多与already ，
yet ，still ，just ，before ，never 等时间副词及by ，before ，until 等引导的短语或从句连用。
如：Before she came to China, Grace had taught English in a middle school for about five years. Peter had collected more than 300 Chinese stamps by the time he was ten.
4. 过去完成时表示某一动作或状态在过去某时之前已经开始，一直延续到这一过去时间，而且动作尚未结束，
仍然有继续下去的可能。
如：By the end of last year, he had worked in the factory for twenty years. （had worked 已
有了20 年，还有继续进行下去的可能）
5. 过去完成时也用于hardly...when... （刚…就…）, no sooner...than... （刚…就…）, It was the first time + that 等一些固
