Je n’ai pas pu dormir

Question

Can you also use ‘je ne pouvais pas dormir’ - if not why please..Thanks Liz

Accepted Answer

Hi Liz, 
Not in this context.
Although,
'Je ne pouvais pas dormir' and 'Je n'ai pas pu dormir'
can both mean, 'I wasn't able to sleep ',
this refers to an action which happened last night ( la nuit dernière) and it is finished which is a classic case for using the passé composé.
Distinguishing between imparfait and passé composé is really tricky for learners as it is almost always because of context.
It is just a question of getting used to it gradually but not easy I know...

Answer

You can use the imperfect tense but it would alter the meaning of the sentence:

Je n'ai pas pu dormir. -- I could not sleep.

Je ne pouvais pas dormir. -- I didn't use to be able to sleep. (i.e., over a longer period of time)