could collapse
Regular verb: collapse - collapsed- collapsed

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could collapse
you could collapse
he could collapse
we could collapse
you could collapse
they could collapse 	I could be collapsing
you could be collapsing
he could be collapsing
we could be collapsing
you could be collapsing
they could be collapsing	I could have collapsed
you could have collapsed
he could have collapsed
we could have collapsed
you could have collapsed
they could have collapsed	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 	V-ing form 	Perfect 	V-ing perfect 	
I couldn't collapse
you couldn't collapse
he couldn't collapse
we couldn't collapse
you couldn't collapse
they couldn't collapse 	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	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	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 	V-ing form 	Perfect 	V-ing perfect 	
could I collapse?
could you collapse?
could he collapse?
could we collapse?
could you collapse?
could they collapse? 	could I be collapsing?
could you be collapsing?
could he be collapsing?
could we be collapsing?
could you be collapsing?
could they be collapsing? 	could I have collapsed?
could you have collapsed?
could he have collapsed?
could we have collapsed?
could you have collapsed?
could they have collapsed? 	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 	V-ing form 	Perfect 	V-ing perfect 	
couldn't I collapse?
couldn't you collapse?
couldn't he collapse?
couldn't we collapse?
couldn't you collapse?
couldn't they collapse? 	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? 	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? 	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?