The principal uses of the present continuous are listed below.
- To set the “background scene” to an event or action. We use the past continuous to describe the background scene and the past simple to describe the event or action:
- I saw him at 8 o’clock on Monday morning while he was waiting for the school bus.
- I was shopping in a supermarket when I noticed a strange-looking man.
- We may have more than one background scene happening concurrently:
- I was lying on my bed and listening to one of my favorite songs.
To emphasize activities which continued for some time but whose exact limits are not known and are not important. Notice the important difference between these two sentences:
- For a while last year I was playing football for my local team and teaching English in the local elementary schools. (It doesn’t indicate whether the actions were completed or not, or whether they happened concurrently)
- Last year I played football for my local team and taught English in the local elementary schools. (It indicates that all of the actions are now complete, and probabley happened in that order)
- Note: state verbs cannot be used in any continuous tense.