intend, mean, hope, want, plan, suppose, expect, think等动词的过去完成时可以用来表示一个本来打算做而未做的事。
I had meant to come, but something happened.
I had intended to call on you, but was prevented from doing so.
They had wanted to help but couldn't get here in time.
一般过去时表示过去时间的动作或状态。过去完成时表示的动作或状态发生在一般过去时表示的动作或状态之前,因此它表示的是"比过去更过去"。
I returned the book that I had borrowed.
He didn't know a thing about the verb, for he had not studied his lessons.
I had been at the bus stop for 20 minutes when a bus finally came.