I could leave you could leave he could leave we could leave you could leave they could leave
V-ing form
I could be leaving you could be leaving he could be leaving we could be leaving you could be leaving they could be leaving
Perfect
I could have left you could have left he could have left we could have left you could have left they could have left
V-ing perfect
I could have been leaving you could have been leaving he could have been leaving we could have been leaving you could have been leaving they could have been leaving
Negation
Simple form
I could not leave you could not leave he could not leave we could not leave you could not leave they could not leave
V-ing form
I could not be leaving you could not be leaving he could not be leaving we could not be leaving you could not be leaving they could not be leaving
Perfect
I could not have left you could not have left he could not have left we could not have left you could not have left they could not have left
V-ing perfect
I could not have been leaving you could not have been leaving he could not have been leaving we could not have been leaving you could not have been leaving they could not have been leaving
Interrogative form
Simple form
could I leave? could you leave? could he leave? could we leave? could you leave? could they leave?
V-ing form
could I be leaving? could you be leaving? could he be leaving? could we be leaving? could you be leaving? could they be leaving?
Perfect
could I have left? could you have left? could he have left? could we have left? could you have left? could they have left?
V-ing perfect
could I have been leaving? could you have been leaving? could he have been leaving? could we have been leaving? could you have been leaving? could they have been leaving?
Interro-negative form
Simple form
could I not leave? could you not leave? could he not leave? could we not leave? could you not leave? could they not leave?
V-ing form
could I not be leaving? could you not be leaving? could he not be leaving? could we not be leaving? could you not be leaving? could they not be leaving?
Perfect
could I not have left? could you not have left? could he not have left? could we not have left? could you not have left? could they not have left?
V-ing perfect
could I not have been leaving? could you not have been leaving? could he not have been leaving? could we not have been leaving? could you not have been leaving? could they not have been leaving?