could blacken
Regular verb: blacken - blackened- blackened

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could blacken
you could blacken
she could blacken
we could blacken
you could blacken
they could blacken 	I could be blackening
you could be blackening
she could be blackening
we could be blackening
you could be blackening
they could be blackening	I could have blackened
you could have blackened
she could have blackened
we could have blackened
you could have blackened
they could have blackened	I could have been blackening
you could have been blackening
she could have been blackening
we could have been blackening
you could have been blackening
they could have been blackening	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I couldn't blacken
you couldn't blacken
she couldn't blacken
we couldn't blacken
you couldn't blacken
they couldn't blacken 	I couldn't be blackening
you couldn't be blackening
she couldn't be blackening
we couldn't be blackening
you couldn't be blackening
they couldn't be blackening	I couldn't have blackened
you couldn't have blackened
she couldn't have blackened
we couldn't have blackened
you couldn't have blackened
they couldn't have blackened	I couldn't have been blackening
you couldn't have been blackening
she couldn't have been blackening
we couldn't have been blackening
you couldn't have been blackening
they couldn't have been blackening	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I blacken?
could you blacken?
could she blacken?
could we blacken?
could you blacken?
could they blacken? 	could I be blackening?
could you be blackening?
could she be blackening?
could we be blackening?
could you be blackening?
could they be blackening? 	could I have blackened?
could you have blackened?
could she have blackened?
could we have blackened?
could you have blackened?
could they have blackened? 	could I have been blackening?
could you have been blackening?
could she have been blackening?
could we have been blackening?
could you have been blackening?
could they have been blackening? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
couldn't I blacken?
couldn't you blacken?
couldn't she blacken?
couldn't we blacken?
couldn't you blacken?
couldn't they blacken? 	couldn't I be blackening?
couldn't you be blackening?
couldn't she be blackening?
couldn't we be blackening?
couldn't you be blackening?
couldn't they be blackening? 	couldn't I have blackened?
couldn't you have blackened?
couldn't she have blackened?
couldn't we have blackened?
couldn't you have blackened?
couldn't they have blackened? 	couldn't I have been blackening?
couldn't you have been blackening?
couldn't she have been blackening?
couldn't we have been blackening?
couldn't you have been blackening?
couldn't they have been blackening?