depuis + Present

The preposition depuis is the standard way to express duration for ongoing events.

1. Two Meanings:
Depending on the context, depuis can translate to:

• Since: When followed by a specific point in time (e.g., depuis 2010).
• For: When followed by a duration of time (e.g., depuis trois jours).

2. The Tense Rule:
Because the action is currently 'live', French uses the present tense (e.g., habite, finit, or attend). If the action was ongoing in the past before being interrupted, use the imparfait.

3. Negation Nuances:

• Use the passé composé for actions that haven't happened for a certain time (e.g., Je ne l'ai pas vu depuis lundi - I haven't seen him since Monday). This is the most common way to express 'hasn't happened for'.
• Use the present tense with ne... pas or ne... plus for ongoing negative states or habits (e.g., Je ne dors pas bien depuis une semaine - I haven't been sleeping well for a week; Je ne fume plus depuis un an - I no longer smoke, and haven't for a year).
• Exception: Using the present tense with ne... pas and depuis longtemps means the action is happening, just not for very long (e.g., Je n'habite pas ici depuis longtemps - I haven't been living here for long).

4. Depuis vs. Depuis que:
Use depuis before a noun or date. Use depuis que when you need to follow it with a subject and a verb (a clause): Depuis qu'il est là... (Since he has been here...). Note that the verb inside a depuis que clause often takes the passé composé if the triggering event was a completed action (e.g., Depuis qu'il est parti, je suis triste - Since he left, I am sad). However, if the triggering state is also ongoing, use the present tense (e.g., Depuis qu'il habite ici, il est heureux - Since he has been living here, he is happy).

5. Asking Questions:
Use depuis quand to ask 'since when' (point in time) and depuis combien de temps to ask 'for how long' (duration).

6. Alternative Structures:
You can also use il y a... que and voilà... que in standard French, or ça fait... que in casual speech: Ça fait deux ans que je suis ici.

7. Adverbial Use:
When used without a following noun or clause, depuis acts as an adverb meaning 'since then' or 'ever since' (e.g., Il est parti et je ne l'ai pas revu depuis. - He left and I haven't seen him since then).

8. Depuis vs. Pendant:
Because English uses 'for' for both ongoing and completed actions, it's important to note the difference in French. Use depuis for actions that are still ongoing. If the action is completely finished, use pendant with a past tense like the passé composé (e.g., J'ai habité à Paris pendant trois ans - I lived in Paris for three years).