could darken
Regular verb: darken - darkened- darkened

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could darken
you could darken
he could darken
we could darken
you could darken
they could darken 	I could be darkening
you could be darkening
he could be darkening
we could be darkening
you could be darkening
they could be darkening	I could have darkened
you could have darkened
he could have darkened
we could have darkened
you could have darkened
they could have darkened	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 	V-ing form 	Perfect 	V-ing perfect 	
I couldn't darken
you couldn't darken
he couldn't darken
we couldn't darken
you couldn't darken
they couldn't darken 	I couldn't be darkening
you couldn't be darkening
he couldn't be darkening
we couldn't be darkening
you couldn't be darkening
they couldn't be darkening	I couldn't have darkened
you couldn't have darkened
he couldn't have darkened
we couldn't have darkened
you couldn't have darkened
they couldn't have darkened	I couldn't have been darkening
you couldn't have been darkening
he couldn't have been darkening
we couldn't have been darkening
you couldn't have been darkening
they couldn't have been darkening	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I darken?
could you darken?
could he darken?
could we darken?
could you darken?
could they darken? 	could I be darkening?
could you be darkening?
could he be darkening?
could we be darkening?
could you be darkening?
could they be darkening? 	could I have darkened?
could you have darkened?
could he have darkened?
could we have darkened?
could you have darkened?
could they have darkened? 	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 	V-ing form 	Perfect 	V-ing perfect 	
couldn't I darken?
couldn't you darken?
couldn't he darken?
couldn't we darken?
couldn't you darken?
couldn't they darken? 	couldn't I be darkening?
couldn't you be darkening?
couldn't he be darkening?
couldn't we be darkening?
couldn't you be darkening?
couldn't they be darkening? 	couldn't I have darkened?
couldn't you have darkened?
couldn't he have darkened?
couldn't we have darkened?
couldn't you have darkened?
couldn't they have darkened? 	couldn't I have been darkening?
couldn't you have been darkening?
couldn't he have been darkening?
couldn't we have been darkening?
couldn't you have been darkening?
couldn't they have been darkening?