I could collapse you could collapse he could collapse we could collapse you could collapse they could collapse
V-ing form
I could be collapsing you could be collapsing he could be collapsing we could be collapsing you could be collapsing they could be collapsing
Perfect
I could have collapsed you could have collapsed he 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 he could have been collapsing we could have been collapsing you could have been collapsing they could have been collapsing
Negation
Simple form
I couldn't collapse you couldn't collapse he couldn't collapse we couldn't collapse you couldn't collapse they couldn't collapse
V-ing form
I couldn't be collapsing you couldn't be collapsing he couldn't be collapsing we couldn't be collapsing you couldn't be collapsing they couldn't be collapsing
Perfect
I couldn't have collapsed you couldn't have collapsed he couldn't have collapsed we couldn't have collapsed you couldn't have collapsed they couldn't have collapsed
V-ing perfect
I couldn't have been collapsing you couldn't have been collapsing he couldn't have been collapsing we couldn't have been collapsing you couldn't have been collapsing they couldn't have been collapsing
Interrogative form
Simple form
could I collapse? could you collapse? could he collapse? could we collapse? could you collapse? could they collapse?
V-ing form
could I be collapsing? could you be collapsing? could he be collapsing? could we be collapsing? could you be collapsing? could they be collapsing?
Perfect
could I have collapsed? could you have collapsed? could he 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 he have been collapsing? could we have been collapsing? could you have been collapsing? could they have been collapsing?
Interro-negative form
Simple form
couldn't I collapse? couldn't you collapse? couldn't he collapse? couldn't we collapse? couldn't you collapse? couldn't they collapse?
V-ing form
couldn't I be collapsing? couldn't you be collapsing? couldn't he be collapsing? couldn't we be collapsing? couldn't you be collapsing? couldn't they be collapsing?
Perfect
couldn't I have collapsed? couldn't you have collapsed? couldn't he have collapsed? couldn't we have collapsed? couldn't you have collapsed? couldn't they have collapsed?
V-ing perfect
couldn't I have been collapsing? couldn't you have been collapsing? couldn't he have been collapsing? couldn't we have been collapsing? couldn't you have been collapsing? couldn't they have been collapsing?