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