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