一、述词过去进行式的结构形式
我们来看下面几个句子：
1. I was watching TV.
2. They were crying.
上面两个句子的述词串由 be 的一般过去式和另外一个主要述词的-ing 形式组在一起形成。这样的结构，我们称之为述词的过去进行式。
二、述词过去进行式表达的时间区间
A. 表示过去
3. They were singing when I got there.
4. I was waiting for a bus when it began to rain.
以上两个句子都采用了述词的过去进行式表达过去某个时间点正在发生某事。
5. Tom and Jerry were always fighting with each other.
6. Jerry was playing football every afternoon.
以上两个句子都采用了述词的过去进行式表达过去经常发生某事。
7. Jerry's Chinese was improving.
8. Her hair was going grey.
以上两个句子都采用述词的过去进行式表达过去持续的变化。
B. 表示现在
9. If Michael Jordan was playing, he would probably win the MVP again. 假如乔丹还在打球，他可能还会赢得“最有价值球员”奖。（但是实际上乔丹不再打篮球了）
例句 9 其实是用 was playing 这个过去进行式来虚拟现在。
10. These seats are very uncomfortable. I wish I was traveling first class. 这些座椅非常不舒服。我真希望我是坐头等舱旅行。（实际上我不是做头等舱）
例句 10 其实也是用 was travelling 这个过去进行式来虚拟现在。
C. 表示将来
11. I wish Tom weren't leaving tomorrow. 我希望Tom明天不要离开。（实际上明天Tom 会离开）
例句 11 其实是用 weren't leaving 这个过去进行式来虚拟将来。