I could smooth you could smooth he could smooth we could smooth you could smooth they could smooth
V-ing form
I could be smoothing you could be smoothing he could be smoothing we could be smoothing you could be smoothing they could be smoothing
Perfect
I could have smoothed you could have smoothed he could have smoothed we could have smoothed you could have smoothed they could have smoothed
V-ing perfect
I could have been smoothing you could have been smoothing he could have been smoothing we could have been smoothing you could have been smoothing they could have been smoothing
Negation
Simple form
I couldn't smooth you couldn't smooth he couldn't smooth we couldn't smooth you couldn't smooth they couldn't smooth
V-ing form
I couldn't be smoothing you couldn't be smoothing he couldn't be smoothing we couldn't be smoothing you couldn't be smoothing they couldn't be smoothing
Perfect
I couldn't have smoothed you couldn't have smoothed he couldn't have smoothed we couldn't have smoothed you couldn't have smoothed they couldn't have smoothed
V-ing perfect
I couldn't have been smoothing you couldn't have been smoothing he couldn't have been smoothing we couldn't have been smoothing you couldn't have been smoothing they couldn't have been smoothing
Interrogative form
Simple form
could I smooth? could you smooth? could he smooth? could we smooth? could you smooth? could they smooth?
V-ing form
could I be smoothing? could you be smoothing? could he be smoothing? could we be smoothing? could you be smoothing? could they be smoothing?
Perfect
could I have smoothed? could you have smoothed? could he have smoothed? could we have smoothed? could you have smoothed? could they have smoothed?
V-ing perfect
could I have been smoothing? could you have been smoothing? could he have been smoothing? could we have been smoothing? could you have been smoothing? could they have been smoothing?
Interro-negative form
Simple form
couldn't I smooth? couldn't you smooth? couldn't he smooth? couldn't we smooth? couldn't you smooth? couldn't they smooth?
V-ing form
couldn't I be smoothing? couldn't you be smoothing? couldn't he be smoothing? couldn't we be smoothing? couldn't you be smoothing? couldn't they be smoothing?
Perfect
couldn't I have smoothed? couldn't you have smoothed? couldn't he have smoothed? couldn't we have smoothed? couldn't you have smoothed? couldn't they have smoothed?
V-ing perfect
couldn't I have been smoothing? couldn't you have been smoothing? couldn't he have been smoothing? couldn't we have been smoothing? couldn't you have been smoothing? couldn't they have been smoothing?