本文讲解考研英语语法之【过去完成时】。语法是英语学习的基础，语法大关不过，阅读、完型、翻译和写作都会有难度，就别提过线和拿高分了。所以说，基础阶段，语法基础要打好。请关注新东方在线2020考研英语语法大全系列文章，我们一起来梳理考研英语所需的基础语法和重点语法：
过去完成时
一律用had + 过去分词构成。
用法：
1)表示发生在过去某一时间或动作之前的事情，即“过去的过去”。用过去完成时，必须有一个过去的时间或动作来作参照，说明在此之前某事已发生。如果两个动作都是在过去发生的，先发生的用过去完成时，后发生的用一般过去时。例如：
She told me she had been there three times before. 她告诉我她以前到过那里三次。(“去过”发生在“告诉”之前)
How long had he taught here by the end of last term? 到上学期末为止，他在这里教学多长时间啦? (“教学”发生在上学期末结束之前)
When we arrived, the football match had already begun. 我们到的时候，足球赛已经开始了。
She had visited China twice before she came this year. 她今年来中国之前已访问过中国两次了。
2)过去完成时动词可以表示过去某一时刻之前发生的动作或呈现的状态，这一动作一直持续到过去这一时刻或将继续下去。例如：
By the middle of last month, I had lived in Beijing for five years. 到上月中旬，我已在北京住了五年了。
By six o’clock they had worked for eight hours. 到六点为止，他们已工作八小时了。
When I came to Shanghai, he had been there for a long time. 我到上海时，他在那里很长时间了。
3)过去完成时动词常用于间接引语和虚拟语气，我们以后会详细讲述。
4)此外，过去完成时常用于 no sooner…than… 和 hardly(scarcely) …when… 这两个句型，前面部分用过去完成时，后面部分用一般过去时。例如：
No sooner had he stolen the purse than he was caught red-handed. = He had no sooner stolen the purse than he was caught red-handed. 他刚偷到钱包就被当场抓获。
Saddam had hardly realized what was happening when he was captured. = Hardly had Saddam realized what was happening when he was captured. 萨达姆还没有意识到在发生什么事情就被抓获了。