I could sell you could sell he could sell we could sell you could sell they could sell
V-ing form
I could be selling you could be selling he could be selling we could be selling you could be selling they could be selling
Perfect
I could have sold you could have sold he could have sold we could have sold you could have sold they could have sold
V-ing perfect
I could have been selling you could have been selling he could have been selling we could have been selling you could have been selling they could have been selling
Negation
Simple form
I could not sell you could not sell he could not sell we could not sell you could not sell they could not sell
V-ing form
I could not be selling you could not be selling he could not be selling we could not be selling you could not be selling they could not be selling
Perfect
I could not have sold you could not have sold he could not have sold we could not have sold you could not have sold they could not have sold
V-ing perfect
I could not have been selling you could not have been selling he could not have been selling we could not have been selling you could not have been selling they could not have been selling
Interrogative form
Simple form
could I sell? could you sell? could he sell? could we sell? could you sell? could they sell?
V-ing form
could I be selling? could you be selling? could he be selling? could we be selling? could you be selling? could they be selling?
Perfect
could I have sold? could you have sold? could he have sold? could we have sold? could you have sold? could they have sold?
V-ing perfect
could I have been selling? could you have been selling? could he have been selling? could we have been selling? could you have been selling? could they have been selling?
Interro-negative form
Simple form
could I not sell? could you not sell? could he not sell? could we not sell? could you not sell? could they not sell?
V-ing form
could I not be selling? could you not be selling? could he not be selling? could we not be selling? could you not be selling? could they not be selling?
Perfect
could I not have sold? could you not have sold? could he not have sold? could we not have sold? could you not have sold? could they not have sold?
V-ing perfect
could I not have been selling? could you not have been selling? could he not have been selling? could we not have been selling? could you not have been selling? could they not have been selling?