I could duck you could duck she could duck we could duck you could duck they could duck
V-ing form
I could be ducking you could be ducking she could be ducking we could be ducking you could be ducking they could be ducking
Perfect
I could have ducked you could have ducked she could have ducked we could have ducked you could have ducked they could have ducked
V-ing perfect
I could have been ducking you could have been ducking she could have been ducking we could have been ducking you could have been ducking they could have been ducking
Negation
Simple form
I could not duck you could not duck she could not duck we could not duck you could not duck they could not duck
V-ing form
I could not be ducking you could not be ducking she could not be ducking we could not be ducking you could not be ducking they could not be ducking
Perfect
I could not have ducked you could not have ducked she could not have ducked we could not have ducked you could not have ducked they could not have ducked
V-ing perfect
I could not have been ducking you could not have been ducking she could not have been ducking we could not have been ducking you could not have been ducking they could not have been ducking
Interrogative form
Simple form
could I duck? could you duck? could she duck? could we duck? could you duck? could they duck?
V-ing form
could I be ducking? could you be ducking? could she be ducking? could we be ducking? could you be ducking? could they be ducking?
Perfect
could I have ducked? could you have ducked? could she have ducked? could we have ducked? could you have ducked? could they have ducked?
V-ing perfect
could I have been ducking? could you have been ducking? could she have been ducking? could we have been ducking? could you have been ducking? could they have been ducking?
Interro-negative form
Simple form
could I not duck? could you not duck? could she not duck? could we not duck? could you not duck? could they not duck?
V-ing form
could I not be ducking? could you not be ducking? could she not be ducking? could we not be ducking? could you not be ducking? could they not be ducking?
Perfect
could I not have ducked? could you not have ducked? could she not have ducked? could we not have ducked? could you not have ducked? could they not have ducked?
V-ing perfect
could I not have been ducking? could you not have been ducking? could she not have been ducking? could we not have been ducking? could you not have been ducking? could they not have been ducking?