I could prealter you could prealter she could prealter we could prealter you could prealter they could prealter
V-ing form
I could be prealtering you could be prealtering she could be prealtering we could be prealtering you could be prealtering they could be prealtering
Perfect
I could have prealtered you could have prealtered she could have prealtered we could have prealtered you could have prealtered they could have prealtered
V-ing perfect
I could have been prealtering you could have been prealtering she could have been prealtering we could have been prealtering you could have been prealtering they could have been prealtering
Negation
Simple form
I could not prealter you could not prealter she could not prealter we could not prealter you could not prealter they could not prealter
V-ing form
I could not be prealtering you could not be prealtering she could not be prealtering we could not be prealtering you could not be prealtering they could not be prealtering
Perfect
I could not have prealtered you could not have prealtered she could not have prealtered we could not have prealtered you could not have prealtered they could not have prealtered
V-ing perfect
I could not have been prealtering you could not have been prealtering she could not have been prealtering we could not have been prealtering you could not have been prealtering they could not have been prealtering
Interrogative form
Simple form
could I prealter? could you prealter? could she prealter? could we prealter? could you prealter? could they prealter?
V-ing form
could I be prealtering? could you be prealtering? could she be prealtering? could we be prealtering? could you be prealtering? could they be prealtering?
Perfect
could I have prealtered? could you have prealtered? could she have prealtered? could we have prealtered? could you have prealtered? could they have prealtered?
V-ing perfect
could I have been prealtering? could you have been prealtering? could she have been prealtering? could we have been prealtering? could you have been prealtering? could they have been prealtering?
Interro-negative form
Simple form
could I not prealter? could you not prealter? could she not prealter? could we not prealter? could you not prealter? could they not prealter?
V-ing form
could I not be prealtering? could you not be prealtering? could she not be prealtering? could we not be prealtering? could you not be prealtering? could they not be prealtering?
Perfect
could I not have prealtered? could you not have prealtered? could she not have prealtered? could we not have prealtered? could you not have prealtered? could they not have prealtered?
V-ing perfect
could I not have been prealtering? could you not have been prealtering? could she not have been prealtering? could we not have been prealtering? could you not have been prealtering? could they not have been prealtering?