Analogy between Present Continuous and Past Continuous

Continuous tenses express unfinished action. The action is in progress at a specific time.

Present Continuous – something which is happening at the moment, at the present moment. The activity is not finished. You are in the middle of doing something. The activity is in progress in the present time.

Past Continuous - something which was happening at a specific moment in the past. The activity was not finished. You were in the middle of doing something. The activity was in progress in the past time.

**************************************************************

Past Continuous – unfinished action in the past

We use Past Continuous:

1. for an action which was in progress at a particular time in the past. We do not know when the action started or finished.

At three o’clock yesterday afternoon, the kids were playing with the dog. (We do not know when they started or finished playing with the dog)

Chris was running at 9 pm yesterday. (We don’t know when he started and when he finished running. We know at  9 pm yesterday, at that time, he was in the middle of running)

2.  For a past action which was in progress when another action interrupted it. We use Past Continuous for the action in progress (the longer action) and Past Simple for the action which interrupted it (the shorter action)

Chris was cooking burgers for breakfast when his landlord knocked on his door. (was cooking = longer action; knocked = shorter action)

3. For two or more actions which were happening at the same time in the past (simultaneous actions).

* Chris was entering the room while the people were working:

** The sun was shining and the birds were singing while I was walking in the park.

4. with a word like always or constantly when there is criticism or complaint:

Your girlfriend was always calling you at the wrong moment:

Another examples:

** She was constantly talking. She annoyed everyone.

*** You were always buying new clothes!

**************************************************

(the whole video here: http://www.youtube.com/watch?v=kUc-jeDr-u0)