I could birdie you could birdie he could birdie we could birdie you could birdie they could birdie
V-ing form
I could be birdying you could be birdying he could be birdying we could be birdying you could be birdying they could be birdying
Perfect
I could have birdied you could have birdied he could have birdied we could have birdied you could have birdied they could have birdied
V-ing perfect
I could have been birdying you could have been birdying he could have been birdying we could have been birdying you could have been birdying they could have been birdying
Negation
Simple form
I could not birdie you could not birdie he could not birdie we could not birdie you could not birdie they could not birdie
V-ing form
I could not be birdying you could not be birdying he could not be birdying we could not be birdying you could not be birdying they could not be birdying
Perfect
I could not have birdied you could not have birdied he could not have birdied we could not have birdied you could not have birdied they could not have birdied
V-ing perfect
I could not have been birdying you could not have been birdying he could not have been birdying we could not have been birdying you could not have been birdying they could not have been birdying
Interrogative form
Simple form
could I birdie? could you birdie? could he birdie? could we birdie? could you birdie? could they birdie?
V-ing form
could I be birdying? could you be birdying? could he be birdying? could we be birdying? could you be birdying? could they be birdying?
Perfect
could I have birdied? could you have birdied? could he have birdied? could we have birdied? could you have birdied? could they have birdied?
V-ing perfect
could I have been birdying? could you have been birdying? could he have been birdying? could we have been birdying? could you have been birdying? could they have been birdying?
Interro-negative form
Simple form
could I not birdie? could you not birdie? could he not birdie? could we not birdie? could you not birdie? could they not birdie?
V-ing form
could I not be birdying? could you not be birdying? could he not be birdying? could we not be birdying? could you not be birdying? could they not be birdying?
Perfect
could I not have birdied? could you not have birdied? could he not have birdied? could we not have birdied? could you not have birdied? could they not have birdied?
V-ing perfect
could I not have been birdying? could you not have been birdying? could he not have been birdying? could we not have been birdying? could you not have been birdying? could they not have been birdying?