I could turn you could turn he could turn we could turn you could turn they could turn
V-ing form
I could be turning you could be turning he could be turning we could be turning you could be turning they could be turning
Perfect
I could have turned you could have turned he could have turned we could have turned you could have turned they could have turned
V-ing perfect
I could have been turning you could have been turning he could have been turning we could have been turning you could have been turning they could have been turning
Negation
Simple form
I could not turn you could not turn he could not turn we could not turn you could not turn they could not turn
V-ing form
I could not be turning you could not be turning he could not be turning we could not be turning you could not be turning they could not be turning
Perfect
I could not have turned you could not have turned he could not have turned we could not have turned you could not have turned they could not have turned
V-ing perfect
I could not have been turning you could not have been turning he could not have been turning we could not have been turning you could not have been turning they could not have been turning
Interrogative form
Simple form
could I turn? could you turn? could he turn? could we turn? could you turn? could they turn?
V-ing form
could I be turning? could you be turning? could he be turning? could we be turning? could you be turning? could they be turning?
Perfect
could I have turned? could you have turned? could he have turned? could we have turned? could you have turned? could they have turned?
V-ing perfect
could I have been turning? could you have been turning? could he have been turning? could we have been turning? could you have been turning? could they have been turning?
Interro-negative form
Simple form
could I not turn? could you not turn? could he not turn? could we not turn? could you not turn? could they not turn?
V-ing form
could I not be turning? could you not be turning? could he not be turning? could we not be turning? could you not be turning? could they not be turning?
Perfect
could I not have turned? could you not have turned? could he not have turned? could we not have turned? could you not have turned? could they not have turned?
V-ing perfect
could I not have been turning? could you not have been turning? could he not have been turning? could we not have been turning? could you not have been turning? could they not have been turning?