Perpendicular actions in Past Continuous. We have 2 actions. One of them is continuous, ongoing action happening in the past. The second action acts as a time-indicator, and it’s not continuous. It’s a complete, finished action. So it can not be parallel to the main incomplete ongoing action. It means this complete action is perpendicular to the other continuous, incomplete action. This complete action is a time-indicator, and it is in Past Simple. Also, the fact that one action is in Past Continuous and the other one is in Past Simple tells us that these 2 actions can not be happening in parallel with each other, so I call them perpendicular actions.
He was watching a movie when my brother came.
The complete action “when my brother came” is a time indicator for the incomplete action – was watching.
Fantastic! Time of action in Past Continuous can be expressed in other ways. Besides perpendicular actions, we have parallel actions! Yes, English is a very interesting language, and we can draw so many analogies with mathematics and geometry! We strongly recommend to study Parallel actions: Past Continuous Tense, so it’s easy for you to understand perpendicular actions.
The 3 conditions when we can use Past Continuous with a perpendicular action:
1. Action was taking place in the past
2. Action was incomplete (i.e. it was continuous)
3. Indication of time the action was taking place. This time indicator is another “perpendicular” complete action, normally in Past Simple.
He was watching a movie when my brother came.
When my brother came, he was watching a movie.
I was watching a movie after / before / when my brother came.
After my brother came, I was watching a movie.
I was watching a movie, and my brother came.
I was watching a movie until my brother came.
As you can see, one complete action shows when the other incomplete action was happening.
While versus when
While I was watching a movie, my brother came.
My brother came while I was watching a movie
While shows duration and followed by a continuous action:
I was watching a movie, when while my brother came.
Use of until
The verb that goes after “until” is in Past Simple.
The ongoing action is interrupted, and it no longer continues.
I was watching a movie, until she came.
Interestingly, the main action is ongoing, and it’s in Past Continuous, while the time-indicator action is complete, and it’s in Past Simple.
Quick recap on perpendicular actions:
Well, very briefly, we use Past Continuous when we have an ongoing action in the past, and something happened during this action. That’s really really briefly, however, it covers probably 80 percent of this particular use.
Also on Past Continuous: