I could sleep you could sleep she could sleep we could sleep you could sleep they could sleep
V-ing form
I could be sleeping you could be sleeping she could be sleeping we could be sleeping you could be sleeping they could be sleeping
Perfect
I could have slept you could have slept she 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 she could have been sleeping we could have been sleeping you could have been sleeping they could have been sleeping
Negation
Simple form
I couldn't sleep you couldn't sleep she couldn't sleep we couldn't sleep you couldn't sleep they couldn't sleep
V-ing form
I couldn't be sleeping you couldn't be sleeping she couldn't be sleeping we couldn't be sleeping you couldn't be sleeping they couldn't be sleeping
Perfect
I couldn't have slept you couldn't have slept she couldn't have slept we couldn't have slept you couldn't have slept they couldn't have slept
V-ing perfect
I couldn't have been sleeping you couldn't have been sleeping she couldn't have been sleeping we couldn't have been sleeping you couldn't have been sleeping they couldn't have been sleeping
Interrogative form
Simple form
could I sleep? could you sleep? could she sleep? could we sleep? could you sleep? could they sleep?
V-ing form
could I be sleeping? could you be sleeping? could she be sleeping? could we be sleeping? could you be sleeping? could they be sleeping?
Perfect
could I have slept? could you have slept? could she 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 she have been sleeping? could we have been sleeping? could you have been sleeping? could they have been sleeping?
Interro-negative form
Simple form
couldn't I sleep? couldn't you sleep? couldn't she sleep? couldn't we sleep? couldn't you sleep? couldn't they sleep?
V-ing form
couldn't I be sleeping? couldn't you be sleeping? couldn't she be sleeping? couldn't we be sleeping? couldn't you be sleeping? couldn't they be sleeping?
Perfect
couldn't I have slept? couldn't you have slept? couldn't she have slept? couldn't we have slept? couldn't you have slept? couldn't they have slept?
V-ing perfect
couldn't I have been sleeping? couldn't you have been sleeping? couldn't she have been sleeping? couldn't we have been sleeping? couldn't you have been sleeping? couldn't they have been sleeping?