（1）过去进行时和一般过去时的基本差别是，过去进行时表示一个正在进行的动作，而一般过去时表示一个已完成的动作。试比较下面的句子。
I was writing an essay.我在写一篇论文。（可能还没写完）
I wrote an essay yesterday.我昨天写了一篇论坛。（已写完）
They were building a skyscraper.他们在建一座摩天大厦。（在修建）
They build a skyscraper.他们盖了一座摩天大厦。（已盖好）
She was knitting a sweater for Tom.她在给Tom织了一件毛衣。
She knitted a sweater for Tom.她给Tom织了一件毛衣。
He was doing his homwork in the afternoon.下午他在做作业。
He did his homework in the afternoon.下午他把作业做完了。
（2）有些动词本身并不表示动作完成，入rain,snow,cough,wear,feel,wait,stay,work等，这时用两种时态意思上差别不大：
It snowed all night.
It was snowing all night
下了一整夜的雪。
She wore a blue coat.
She was wearing a blue coat
她穿着一件蓝外套。
He felt a bit uneasy.
He was feeling a bit uneasy.
他感到有点不自在。
We stayed in a hotel.
We were staying in a hotel.
我们住在旅馆里。
（3）用进行时态有时有感情色彩，特别是带有always，forever，constantly这类状语时，如：
He was always ringing me up.他老是给我打电话。（厌烦）
She was always working.她总是不停地干活。（赞扬）
The old lady was forever grumbling.这老太太老是嘀嘀咕咕。（厌烦）
He was constantly changing his mind.他老是改变主意。（不以为然）
（4）有时用过去时表示现在的想法，可以显得客气一点，如：
I was wondering whether you could give me some advice.不知你能否帮我出点主意。
I was thinking maybe he could go by taxi.我在想或许他可以做的士去。
I was hoping you could reconsider our proposal.我希望你能再考虑一下我们的建议。
