I could sort you could sort he could sort we could sort you could sort they could sort
V-ing form
I could be sorting you could be sorting he could be sorting we could be sorting you could be sorting they could be sorting
Perfect
I could have sorted you could have sorted he could have sorted we could have sorted you could have sorted they could have sorted
V-ing perfect
I could have been sorting you could have been sorting he could have been sorting we could have been sorting you could have been sorting they could have been sorting
Negation
Simple form
I could not sort you could not sort he could not sort we could not sort you could not sort they could not sort
V-ing form
I could not be sorting you could not be sorting he could not be sorting we could not be sorting you could not be sorting they could not be sorting
Perfect
I could not have sorted you could not have sorted he could not have sorted we could not have sorted you could not have sorted they could not have sorted
V-ing perfect
I could not have been sorting you could not have been sorting he could not have been sorting we could not have been sorting you could not have been sorting they could not have been sorting
Interrogative form
Simple form
could I sort? could you sort? could he sort? could we sort? could you sort? could they sort?
V-ing form
could I be sorting? could you be sorting? could he be sorting? could we be sorting? could you be sorting? could they be sorting?
Perfect
could I have sorted? could you have sorted? could he have sorted? could we have sorted? could you have sorted? could they have sorted?
V-ing perfect
could I have been sorting? could you have been sorting? could he have been sorting? could we have been sorting? could you have been sorting? could they have been sorting?
Interro-negative form
Simple form
could I not sort? could you not sort? could he not sort? could we not sort? could you not sort? could they not sort?
V-ing form
could I not be sorting? could you not be sorting? could he not be sorting? could we not be sorting? could you not be sorting? could they not be sorting?
Perfect
could I not have sorted? could you not have sorted? could he not have sorted? could we not have sorted? could you not have sorted? could they not have sorted?
V-ing perfect
could I not have been sorting? could you not have been sorting? could he not have been sorting? could we not have been sorting? could you not have been sorting? could they not have been sorting?