I could sleep you could sleep he could sleep we could sleep you could sleep they could sleep
V-ing form
I could be sleeping you could be sleeping he could be sleeping we could be sleeping you could be sleeping they could be sleeping
Perfect
I could have slept you could have slept he could have slept we could have slept you could have slept they could have slept
V-ing perfect
I could have been sleeping you could have been sleeping he could have been sleeping we could have been sleeping you could have been sleeping they could have been sleeping
Negation
Simple form
I could not sleep you could not sleep he could not sleep we could not sleep you could not sleep they could not sleep
V-ing form
I could not be sleeping you could not be sleeping he could not be sleeping we could not be sleeping you could not be sleeping they could not be sleeping
Perfect
I could not have slept you could not have slept he could not have slept we could not have slept you could not have slept they could not have slept
V-ing perfect
I could not have been sleeping you could not have been sleeping he could not have been sleeping we could not have been sleeping you could not have been sleeping they could not have been sleeping
Interrogative form
Simple form
could I sleep? could you sleep? could he sleep? could we sleep? could you sleep? could they sleep?
V-ing form
could I be sleeping? could you be sleeping? could he be sleeping? could we be sleeping? could you be sleeping? could they be sleeping?
Perfect
could I have slept? could you have slept? could he have slept? could we have slept? could you have slept? could they have slept?
V-ing perfect
could I have been sleeping? could you have been sleeping? could he have been sleeping? could we have been sleeping? could you have been sleeping? could they have been sleeping?
Interro-negative form
Simple form
could I not sleep? could you not sleep? could he not sleep? could we not sleep? could you not sleep? could they not sleep?
V-ing form
could I not be sleeping? could you not be sleeping? could he not be sleeping? could we not be sleeping? could you not be sleeping? could they not be sleeping?
Perfect
could I not have slept? could you not have slept? could he not have slept? could we not have slept? could you not have slept? could they not have slept?
V-ing perfect
could I not have been sleeping? could you not have been sleeping? could he not have been sleeping? could we not have been sleeping? could you not have been sleeping? could they not have been sleeping?