must blacken
Regular verb: blacken - blackened- blackened

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

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

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

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