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 could not sing you could not sing he could not sing we could not sing you could not sing they could not sing
V-ing form
I could not be singing you could not be singing he could not be singing we could not be singing you could not be singing they could not be singing
Perfect
I could not have sung you could not have sung he could not have sung we could not have sung you could not have sung they could not have sung
V-ing perfect
I could not have been singing you could not have been singing he could not have been singing we could not have been singing you could not have been singing they could not 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
could I not sing? could you not sing? could he not sing? could we not sing? could you not sing? could they not sing?
V-ing form
could I not be singing? could you not be singing? could he not be singing? could we not be singing? could you not be singing? could they not be singing?
Perfect
could I not have sung? could you not have sung? could he not have sung? could we not have sung? could you not have sung? could they not have sung?
V-ing perfect
could I not have been singing? could you not have been singing? could he not have been singing? could we not have been singing? could you not have been singing? could they not have been singing?