I could brighten you could brighten he could brighten we could brighten you could brighten they could brighten
V-ing form
I could be brightening you could be brightening he could be brightening we could be brightening you could be brightening they could be brightening
Perfect
I could have brightened you could have brightened he could have brightened we could have brightened you could have brightened they could have brightened
V-ing perfect
I could have been brightening you could have been brightening he could have been brightening we could have been brightening you could have been brightening they could have been brightening
Negation
Simple form
I could not brighten you could not brighten he could not brighten we could not brighten you could not brighten they could not brighten
V-ing form
I could not be brightening you could not be brightening he could not be brightening we could not be brightening you could not be brightening they could not be brightening
Perfect
I could not have brightened you could not have brightened he could not have brightened we could not have brightened you could not have brightened they could not have brightened
V-ing perfect
I could not have been brightening you could not have been brightening he could not have been brightening we could not have been brightening you could not have been brightening they could not have been brightening
Interrogative form
Simple form
could I brighten? could you brighten? could he brighten? could we brighten? could you brighten? could they brighten?
V-ing form
could I be brightening? could you be brightening? could he be brightening? could we be brightening? could you be brightening? could they be brightening?
Perfect
could I have brightened? could you have brightened? could he have brightened? could we have brightened? could you have brightened? could they have brightened?
V-ing perfect
could I have been brightening? could you have been brightening? could he have been brightening? could we have been brightening? could you have been brightening? could they have been brightening?
Interro-negative form
Simple form
could I not brighten? could you not brighten? could he not brighten? could we not brighten? could you not brighten? could they not brighten?
V-ing form
could I not be brightening? could you not be brightening? could he not be brightening? could we not be brightening? could you not be brightening? could they not be brightening?
Perfect
could I not have brightened? could you not have brightened? could he not have brightened? could we not have brightened? could you not have brightened? could they not have brightened?
V-ing perfect
could I not have been brightening? could you not have been brightening? could he not have been brightening? could we not have been brightening? could you not have been brightening? could they not have been brightening?