could circulate
Regular verb: circulate - circulated- circulated

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could circulate
you could circulate
he could circulate
we could circulate
you could circulate
they could circulate 	I could be circulating
you could be circulating
he could be circulating
we could be circulating
you could be circulating
they could be circulating	I could have circulated
you could have circulated
he could have circulated
we could have circulated
you could have circulated
they could have circulated	I could have been circulating
you could have been circulating
he could have been circulating
we could have been circulating
you could have been circulating
they could have been circulating	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I couldn't circulate
you couldn't circulate
he couldn't circulate
we couldn't circulate
you couldn't circulate
they couldn't circulate 	I couldn't be circulating
you couldn't be circulating
he couldn't be circulating
we couldn't be circulating
you couldn't be circulating
they couldn't be circulating	I couldn't have circulated
you couldn't have circulated
he couldn't have circulated
we couldn't have circulated
you couldn't have circulated
they couldn't have circulated	I couldn't have been circulating
you couldn't have been circulating
he couldn't have been circulating
we couldn't have been circulating
you couldn't have been circulating
they couldn't have been circulating	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I circulate?
could you circulate?
could he circulate?
could we circulate?
could you circulate?
could they circulate? 	could I be circulating?
could you be circulating?
could he be circulating?
could we be circulating?
could you be circulating?
could they be circulating? 	could I have circulated?
could you have circulated?
could he have circulated?
could we have circulated?
could you have circulated?
could they have circulated? 	could I have been circulating?
could you have been circulating?
could he have been circulating?
could we have been circulating?
could you have been circulating?
could they have been circulating? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
couldn't I circulate?
couldn't you circulate?
couldn't he circulate?
couldn't we circulate?
couldn't you circulate?
couldn't they circulate? 	couldn't I be circulating?
couldn't you be circulating?
couldn't he be circulating?
couldn't we be circulating?
couldn't you be circulating?
couldn't they be circulating? 	couldn't I have circulated?
couldn't you have circulated?
couldn't he have circulated?
couldn't we have circulated?
couldn't you have circulated?
couldn't they have circulated? 	couldn't I have been circulating?
couldn't you have been circulating?
couldn't he have been circulating?
couldn't we have been circulating?
couldn't you have been circulating?
couldn't they have been circulating?