Devais vs ai dû

Question

Why is "I had to read a poem" given the imperfect here? The lesson flagged under the answer (Using "devoir" in the imperfect tense versus the compound past in French (L'Imparfait vs Le Passé Composé)) suggests it should be passé composé, since it refers to an obligation that was completed.

Cécile Janty-Davies · Accepted Answer

Bonjour Adrian,
Good question!
The imparfait is used here because 'devais' describes the background context or ongoing state that explains why you were nervous.
In French, the imparfait is used for:
Ongoing situations or states in the past - "I had to read" (this was the situation). Background information that sets the scene for other events
The sentence structure shows this perfectly:
J'étais nerveuse = ongoing state/feeling
... parce que je devais lire = the ongoing obligation that caused that feeling
If you used the passé composé ('j'ai dû lire'), it would mean something different - it would emphasize a specific, completed action:
'I had to read (and I did).'
But here, you're explaining the emotional state you were in because of the looming obligation, not reporting that you completed the reading.
Think of it this way-
The obligation to read the poem was hanging over you, creating your nervousness. That persistent, background situation calls for the imparfait.
Hope this helps!