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