I could backcheck you could backcheck he could backcheck we could backcheck you could backcheck they could backcheck
V-ing form
I could be backchecking you could be backchecking he could be backchecking we could be backchecking you could be backchecking they could be backchecking
Perfect
I could have backchecked you could have backchecked he could have backchecked we could have backchecked you could have backchecked they could have backchecked
V-ing perfect
I could have been backchecking you could have been backchecking he could have been backchecking we could have been backchecking you could have been backchecking they could have been backchecking
Negation
Simple form
I could not backcheck you could not backcheck he could not backcheck we could not backcheck you could not backcheck they could not backcheck
V-ing form
I could not be backchecking you could not be backchecking he could not be backchecking we could not be backchecking you could not be backchecking they could not be backchecking
Perfect
I could not have backchecked you could not have backchecked he could not have backchecked we could not have backchecked you could not have backchecked they could not have backchecked
V-ing perfect
I could not have been backchecking you could not have been backchecking he could not have been backchecking we could not have been backchecking you could not have been backchecking they could not have been backchecking
Interrogative form
Simple form
could I backcheck? could you backcheck? could he backcheck? could we backcheck? could you backcheck? could they backcheck?
V-ing form
could I be backchecking? could you be backchecking? could he be backchecking? could we be backchecking? could you be backchecking? could they be backchecking?
Perfect
could I have backchecked? could you have backchecked? could he have backchecked? could we have backchecked? could you have backchecked? could they have backchecked?
V-ing perfect
could I have been backchecking? could you have been backchecking? could he have been backchecking? could we have been backchecking? could you have been backchecking? could they have been backchecking?
Interro-negative form
Simple form
could I not backcheck? could you not backcheck? could he not backcheck? could we not backcheck? could you not backcheck? could they not backcheck?
V-ing form
could I not be backchecking? could you not be backchecking? could he not be backchecking? could we not be backchecking? could you not be backchecking? could they not be backchecking?
Perfect
could I not have backchecked? could you not have backchecked? could he not have backchecked? could we not have backchecked? could you not have backchecked? could they not have backchecked?
V-ing perfect
could I not have been backchecking? could you not have been backchecking? could he not have been backchecking? could we not have been backchecking? could you not have been backchecking? could they not have been backchecking?