could blacken
Regular verb: blacken - blackened- blackened

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could blacken
you could blacken
he could blacken
we could blacken
you could blacken
they could blacken 	I could be blackening
you could be blackening
he could be blackening
we could be blackening
you could be blackening
they could be blackening	I could have blackened
you could have blackened
he 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
he 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 could not blacken
you could not blacken
he could not blacken
we could not blacken
you could not blacken
they could not blacken 	I could not be blackening
you could not be blackening
he could not be blackening
we could not be blackening
you could not be blackening
they could not be blackening	I could not have blackened
you could not have blackened
he could not have blackened
we could not have blackened
you could not have blackened
they could not have blackened	I could not have been blackening
you could not have been blackening
he could not have been blackening
we could not have been blackening
you could not have been blackening
they could not have been blackening	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I blacken?
could you blacken?
could he blacken?
could we blacken?
could you blacken?
could they blacken? 	could I be blackening?
could you be blackening?
could he be blackening?
could we be blackening?
could you be blackening?
could they be blackening? 	could I have blackened?
could you have blackened?
could he 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 he 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 	
could I not blacken?
could you not blacken?
could he not blacken?
could we not blacken?
could you not blacken?
could they not blacken? 	could I not be blackening?
could you not be blackening?
could he not be blackening?
could we not be blackening?
could you not be blackening?
could they not be blackening? 	could I not have blackened?
could you not have blackened?
could he not have blackened?
could we not have blackened?
could you not have blackened?
could they not have blackened? 	could I not have been blackening?
could you not have been blackening?
could he not have been blackening?
could we not have been blackening?
could you not have been blackening?
could they not have been blackening?