I could chirp you could chirp he could chirp we could chirp you could chirp they could chirp
V-ing form
I could be chirping you could be chirping he could be chirping we could be chirping you could be chirping they could be chirping
Perfect
I could have chirped you could have chirped he could have chirped we could have chirped you could have chirped they could have chirped
V-ing perfect
I could have been chirping you could have been chirping he could have been chirping we could have been chirping you could have been chirping they could have been chirping
Negation
Simple form
I could not chirp you could not chirp he could not chirp we could not chirp you could not chirp they could not chirp
V-ing form
I could not be chirping you could not be chirping he could not be chirping we could not be chirping you could not be chirping they could not be chirping
Perfect
I could not have chirped you could not have chirped he could not have chirped we could not have chirped you could not have chirped they could not have chirped
V-ing perfect
I could not have been chirping you could not have been chirping he could not have been chirping we could not have been chirping you could not have been chirping they could not have been chirping
Interrogative form
Simple form
could I chirp? could you chirp? could he chirp? could we chirp? could you chirp? could they chirp?
V-ing form
could I be chirping? could you be chirping? could he be chirping? could we be chirping? could you be chirping? could they be chirping?
Perfect
could I have chirped? could you have chirped? could he have chirped? could we have chirped? could you have chirped? could they have chirped?
V-ing perfect
could I have been chirping? could you have been chirping? could he have been chirping? could we have been chirping? could you have been chirping? could they have been chirping?
Interro-negative form
Simple form
could I not chirp? could you not chirp? could he not chirp? could we not chirp? could you not chirp? could they not chirp?
V-ing form
could I not be chirping? could you not be chirping? could he not be chirping? could we not be chirping? could you not be chirping? could they not be chirping?
Perfect
could I not have chirped? could you not have chirped? could he not have chirped? could we not have chirped? could you not have chirped? could they not have chirped?
V-ing perfect
could I not have been chirping? could you not have been chirping? could he not have been chirping? could we not have been chirping? could you not have been chirping? could they not have been chirping?