Learn French: Ils voulaient prolonger le voyage, mais ce n'était pas possible. - They wanted to extend the trip, but it was not possible.

In the imparfait, voulaient simply describes an ongoing state of mind or a desire they held: they wanted to. If we used the passé composé (ils ont voulu), the meaning shifts from a state to an action, usually meaning they made a firm decision to or they actually tried to extend the trip.

Why is it ce n'était pas possible instead of il n'était pas possible?

We use ce (which becomes c' before the vowel) because it acts as a pronoun referring back to the entire previous idea of extending the trip. You would use il as an impersonal subject if you stated the action right after, such as il n'était pas possible de prolonger le voyage.

Could I use étendre to mean "to extend" in this sentence?

No, étendre is mostly used for physical expansion, spreading out, or stretching (like spreading a towel or stretching your arms). When extending time, a duration, or a deadline like a trip, French uses prolonger.

Why is the second verb était also in the imparfait?

The phrase ce n'était pas possible describes the general conditions or reality of the situation at that time. The imparfait is used here because it sets the backdrop or describes a past state, rather than a single, sudden completed event.