Learn French: Autrefois, nous imaginions une histoire dans la cour. - In the past, we used to imagine a story in the yard.

To form the imparfait, we start with the present tense nous form. For imaginer (to imagine), that is nous imaginons. We drop the -ons to get the stem (imagin-) and add the imparfait ending for nous, which is -ions. This gives us nous imaginions.

Why use the imparfait tense here instead of the passé composé?

The imparfait is used for ongoing, repeated, or habitual actions in the past. The clue here is the word autrefois (in the past), which sets up a habit: "we used to imagine". The passé composé (nous avons imaginé) would mean we imagined a story just once on a specific occasion.

Is there a trick to hearing the difference between the present nous imaginons and the past nous imaginions?

Yes! Listen for the "y" sound. The present tense ending -ons just has a nasal "ohn" sound. The imparfait ending -ions starts with a "y" sound (like "yohn"). That little glide tells you it is in the past.

Does histoire mean "story" or "history"?

It can mean both! You have to use context to tell them apart. Since the sentence talks about using imagination in the yard (dans la cour), "story" makes perfect sense here.