past continuous

1. To describe incomplete action that was interrupted by another action or event, eg "I was having a beautiful dream when the alarm clock rang."

1.1. *Yesterday he was studying English.

1.2. *John was playing tennis at 10 a.m.

2. The "simple past" describes a completed past action.

3. Another difference between the two times is that "past continuous" is sometimes used to indicate that the action is more casual, less planned.

3.1. *They were singing when I broke the window.

3.2. *When I left, he was studying the lesson

4. Sometimes two simultaneous actions took place in the past described

4.1. Yesterday evening when you called me I was having a shower

4.2. When the parents arrived home the children were watching TV