Depuis with Passé Composé

Question

If a date or measurement of time is not included in a sentence, can you use passé composé with depuis? Examples:

"On parle de ce qui s'est passé depuis qu'on s'est vues."

" Depuis quelques années, le lac a diminué."

Thank you!

Cécile Janty-Davies · Accepted Answer

Hi Helen,
You can use the passé composé with depuis after certain negative sentences and the following Kwiziq lesson will give you some examples -
https://french.kwiziq.com/revision/grammar/when-to-use-either-le-passe-compose-or-le-present-in-negative-sentences-with-depuis
Your example of the lake is interesting because if you use the passé composé,  it indicates that the level has stabilized.
But if you used the present tense -
Le lac diminue depuis quelques années
you have the impression that this lowering of the lake level is ongoing.
Interesting question, sorry about the delay...

Chris Wirt · Answer

The first sentence seems ok to me. In the second sentence I would use the present tense, indicating that the lake has started to shrink in the past and is still continuing now: Depuis quelques années, le lac diminue.