I could collapse you could collapse she could collapse we could collapse you could collapse they could collapse
V-ing form
I could be collapsing you could be collapsing she could be collapsing we could be collapsing you could be collapsing they could be collapsing
Perfect
I could have collapsed you could have collapsed she could have collapsed we could have collapsed you could have collapsed they could have collapsed
V-ing perfect
I could have been collapsing you could have been collapsing she could have been collapsing we could have been collapsing you could have been collapsing they could have been collapsing
Negation
Simple form
I could not collapse you could not collapse she could not collapse we could not collapse you could not collapse they could not collapse
V-ing form
I could not be collapsing you could not be collapsing she could not be collapsing we could not be collapsing you could not be collapsing they could not be collapsing
Perfect
I could not have collapsed you could not have collapsed she could not have collapsed we could not have collapsed you could not have collapsed they could not have collapsed
V-ing perfect
I could not have been collapsing you could not have been collapsing she could not have been collapsing we could not have been collapsing you could not have been collapsing they could not have been collapsing
Interrogative form
Simple form
could I collapse? could you collapse? could she collapse? could we collapse? could you collapse? could they collapse?
V-ing form
could I be collapsing? could you be collapsing? could she be collapsing? could we be collapsing? could you be collapsing? could they be collapsing?
Perfect
could I have collapsed? could you have collapsed? could she have collapsed? could we have collapsed? could you have collapsed? could they have collapsed?
V-ing perfect
could I have been collapsing? could you have been collapsing? could she have been collapsing? could we have been collapsing? could you have been collapsing? could they have been collapsing?
Interro-negative form
Simple form
could I not collapse? could you not collapse? could she not collapse? could we not collapse? could you not collapse? could they not collapse?
V-ing form
could I not be collapsing? could you not be collapsing? could she not be collapsing? could we not be collapsing? could you not be collapsing? could they not be collapsing?
Perfect
could I not have collapsed? could you not have collapsed? could she not have collapsed? could we not have collapsed? could you not have collapsed? could they not have collapsed?
V-ing perfect
could I not have been collapsing? could you not have been collapsing? could she not have been collapsing? could we not have been collapsing? could you not have been collapsing? could they not have been collapsing?