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 couldn't turn you couldn't turn he couldn't turn we couldn't turn you couldn't turn they couldn't turn
V-ing form
I couldn't be turning you couldn't be turning he couldn't be turning we couldn't be turning you couldn't be turning they couldn't be turning
Perfect
I couldn't have turned you couldn't have turned he couldn't have turned we couldn't have turned you couldn't have turned they couldn't have turned
V-ing perfect
I couldn't have been turning you couldn't have been turning he couldn't have been turning we couldn't have been turning you couldn't have been turning they couldn't 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
couldn't I turn? couldn't you turn? couldn't he turn? couldn't we turn? couldn't you turn? couldn't they turn?
V-ing form
couldn't I be turning? couldn't you be turning? couldn't he be turning? couldn't we be turning? couldn't you be turning? couldn't they be turning?
Perfect
couldn't I have turned? couldn't you have turned? couldn't he have turned? couldn't we have turned? couldn't you have turned? couldn't they have turned?
V-ing perfect
couldn't I have been turning? couldn't you have been turning? couldn't he have been turning? couldn't we have been turning? couldn't you have been turning? couldn't they have been turning?