I could sharpen you could sharpen she could sharpen we could sharpen you could sharpen they could sharpen
V-ing form
I could be sharpening you could be sharpening she could be sharpening we could be sharpening you could be sharpening they could be sharpening
Perfect
I could have sharpened you could have sharpened she could have sharpened we could have sharpened you could have sharpened they could have sharpened
V-ing perfect
I could have been sharpening you could have been sharpening she could have been sharpening we could have been sharpening you could have been sharpening they could have been sharpening
Negation
Simple form
I could not sharpen you could not sharpen she could not sharpen we could not sharpen you could not sharpen they could not sharpen
V-ing form
I could not be sharpening you could not be sharpening she could not be sharpening we could not be sharpening you could not be sharpening they could not be sharpening
Perfect
I could not have sharpened you could not have sharpened she could not have sharpened we could not have sharpened you could not have sharpened they could not have sharpened
V-ing perfect
I could not have been sharpening you could not have been sharpening she could not have been sharpening we could not have been sharpening you could not have been sharpening they could not have been sharpening
Interrogative form
Simple form
could I sharpen? could you sharpen? could she sharpen? could we sharpen? could you sharpen? could they sharpen?
V-ing form
could I be sharpening? could you be sharpening? could she be sharpening? could we be sharpening? could you be sharpening? could they be sharpening?
Perfect
could I have sharpened? could you have sharpened? could she have sharpened? could we have sharpened? could you have sharpened? could they have sharpened?
V-ing perfect
could I have been sharpening? could you have been sharpening? could she have been sharpening? could we have been sharpening? could you have been sharpening? could they have been sharpening?
Interro-negative form
Simple form
could I not sharpen? could you not sharpen? could she not sharpen? could we not sharpen? could you not sharpen? could they not sharpen?
V-ing form
could I not be sharpening? could you not be sharpening? could she not be sharpening? could we not be sharpening? could you not be sharpening? could they not be sharpening?
Perfect
could I not have sharpened? could you not have sharpened? could she not have sharpened? could we not have sharpened? could you not have sharpened? could they not have sharpened?
V-ing perfect
could I not have been sharpening? could you not have been sharpening? could she not have been sharpening? could we not have been sharpening? could you not have been sharpening? could they not have been sharpening?