I could talk you could talk he could talk we could talk you could talk they could talk
V-ing form
I could be talking you could be talking he could be talking we could be talking you could be talking they could be talking
Perfect
I could have talked you could have talked he could have talked we could have talked you could have talked they could have talked
V-ing perfect
I could have been talking you could have been talking he could have been talking we could have been talking you could have been talking they could have been talking
Negation
Simple form
I could not talk you could not talk he could not talk we could not talk you could not talk they could not talk
V-ing form
I could not be talking you could not be talking he could not be talking we could not be talking you could not be talking they could not be talking
Perfect
I could not have talked you could not have talked he could not have talked we could not have talked you could not have talked they could not have talked
V-ing perfect
I could not have been talking you could not have been talking he could not have been talking we could not have been talking you could not have been talking they could not have been talking
Interrogative form
Simple form
could I talk? could you talk? could he talk? could we talk? could you talk? could they talk?
V-ing form
could I be talking? could you be talking? could he be talking? could we be talking? could you be talking? could they be talking?
Perfect
could I have talked? could you have talked? could he have talked? could we have talked? could you have talked? could they have talked?
V-ing perfect
could I have been talking? could you have been talking? could he have been talking? could we have been talking? could you have been talking? could they have been talking?
Interro-negative form
Simple form
could I not talk? could you not talk? could he not talk? could we not talk? could you not talk? could they not talk?
V-ing form
could I not be talking? could you not be talking? could he not be talking? could we not be talking? could you not be talking? could they not be talking?
Perfect
could I not have talked? could you not have talked? could he not have talked? could we not have talked? could you not have talked? could they not have talked?
V-ing perfect
could I not have been talking? could you not have been talking? could he not have been talking? could we not have been talking? could you not have been talking? could they not have been talking?