Passé composé or imparfait? Set the scene
Separate what was happening from the event that happened within it.
The imparfait shows the background or an ongoing situation. The passé composé presents an event as completed.
Set the background
Start with what was already happening. You are setting the scene.
Il pleuvait.
It was raining.
Je lisais près de la fenêtre.
I was reading near the window.
These forms show situations in progress, without focusing on their beginning or end.
Add the event
Now add a completed event within that background.
The phone rings during the rain. The rain sets the scene; the ringing is presented as an event.
Length alone does not decide the tense. A long action can be presented as completed; a short one can be shown in progress.
Choose for the situation
Could reading use the passé composé instead?
Yes, with a different viewpoint: J’ai lu ce livre pendant les vacances. This presents reading the book as a completed event during the holidays. Choose for the situation, not just the verb.
French examples are marked in their original language. Answer explanations are available before or after an attempt.