过去将来时是一种英语时态，用于描述从过去某一特定时间点来看将要发生的动作或呈现的状态。其核心特点如下：

时间基准

过去将来时的时间基准是过去，即从过去某一时刻推算出的未来动作或状态。例如，"I thought I would finish the task by 5 PM" 中的"would finish"是从过去的时间点（如昨天或过去某个时刻）来看待未来（5 PM）的动作。

结构与用法

基本结构：

主语 + be动词（was/were）+ going to + 动词原形

例如：

He was going to call you last night.

They were going to launch the product in June.

特殊结构：主语 + would + 动词原形

例如：

I thought I would be a doctor by 30.

She wondered if we would travel to Japan.

使用场景：常用于宾语从句中，如：

The meeting started when we arrived.

与一般过去时的区别

虽然过去将来时和一般过去时都涉及过去时间，但过去将来时强调对未来动作的预测或计划，而一般过去时描述过去实际发生的动作。例如：

过去将来时：She was going to call you at 3 PM.

一般过去时：She called you at 3 PM.

典型例句

The letter arrived when I was reading a book.

They expected the guests to arrive by 7 PM.

I imagined myself winning the award.

通过以上要点，可以清晰理解过去将来时的定义及应用场景。