I could darken you could darken he could darken we could darken you could darken they could darken
V-ing form
I could be darkening you could be darkening he could be darkening we could be darkening you could be darkening they could be darkening
Perfect
I could have darkened you could have darkened he could have darkened we could have darkened you could have darkened they could have darkened
V-ing perfect
I could have been darkening you could have been darkening he could have been darkening we could have been darkening you could have been darkening they could have been darkening
Negation
Simple form
I could not darken you could not darken he could not darken we could not darken you could not darken they could not darken
V-ing form
I could not be darkening you could not be darkening he could not be darkening we could not be darkening you could not be darkening they could not be darkening
Perfect
I could not have darkened you could not have darkened he could not have darkened we could not have darkened you could not have darkened they could not have darkened
V-ing perfect
I could not have been darkening you could not have been darkening he could not have been darkening we could not have been darkening you could not have been darkening they could not have been darkening
Interrogative form
Simple form
could I darken? could you darken? could he darken? could we darken? could you darken? could they darken?
V-ing form
could I be darkening? could you be darkening? could he be darkening? could we be darkening? could you be darkening? could they be darkening?
Perfect
could I have darkened? could you have darkened? could he have darkened? could we have darkened? could you have darkened? could they have darkened?
V-ing perfect
could I have been darkening? could you have been darkening? could he have been darkening? could we have been darkening? could you have been darkening? could they have been darkening?
Interro-negative form
Simple form
could I not darken? could you not darken? could he not darken? could we not darken? could you not darken? could they not darken?
V-ing form
could I not be darkening? could you not be darkening? could he not be darkening? could we not be darkening? could you not be darkening? could they not be darkening?
Perfect
could I not have darkened? could you not have darkened? could he not have darkened? could we not have darkened? could you not have darkened? could they not have darkened?
V-ing perfect
could I not have been darkening? could you not have been darkening? could he not have been darkening? could we not have been darkening? could you not have been darkening? could they not have been darkening?