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