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, said, knew, heard, thought等动词后的宾语从句。如：

She said that she had seen the film before.

( 2 )状语从句中

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.