I could box you could box he could box we could box you could box they could box
V-ing form
I could be boxing you could be boxing he could be boxing we could be boxing you could be boxing they could be boxing
Perfect
I could have boxed you could have boxed he could have boxed we could have boxed you could have boxed they could have boxed
V-ing perfect
I could have been boxing you could have been boxing he could have been boxing we could have been boxing you could have been boxing they could have been boxing
Negation
Simple form
I could not box you could not box he could not box we could not box you could not box they could not box
V-ing form
I could not be boxing you could not be boxing he could not be boxing we could not be boxing you could not be boxing they could not be boxing
Perfect
I could not have boxed you could not have boxed he could not have boxed we could not have boxed you could not have boxed they could not have boxed
V-ing perfect
I could not have been boxing you could not have been boxing he could not have been boxing we could not have been boxing you could not have been boxing they could not have been boxing
Interrogative form
Simple form
could I box? could you box? could he box? could we box? could you box? could they box?
V-ing form
could I be boxing? could you be boxing? could he be boxing? could we be boxing? could you be boxing? could they be boxing?
Perfect
could I have boxed? could you have boxed? could he have boxed? could we have boxed? could you have boxed? could they have boxed?
V-ing perfect
could I have been boxing? could you have been boxing? could he have been boxing? could we have been boxing? could you have been boxing? could they have been boxing?
Interro-negative form
Simple form
could I not box? could you not box? could he not box? could we not box? could you not box? could they not box?
V-ing form
could I not be boxing? could you not be boxing? could he not be boxing? could we not be boxing? could you not be boxing? could they not be boxing?
Perfect
could I not have boxed? could you not have boxed? could he not have boxed? could we not have boxed? could you not have boxed? could they not have boxed?
V-ing perfect
could I not have been boxing? could you not have been boxing? could he not have been boxing? could we not have been boxing? could you not have been boxing? could they not have been boxing?