must blacken
Regular verb: blacken - blackened- blackened

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

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
must I blacken?
must you blacken?
must she blacken?
must we blacken?
must you blacken?
must they blacken? 	must I be blackening?
must you be blackening?
must she be blackening?
must we be blackening?
must you be blackening?
must they be blackening? 	must I have blackened?
must you have blackened?
must she 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 she 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 	
mustn't I blacken?
mustn't you blacken?
mustn't she blacken?
mustn't we blacken?
mustn't you blacken?
mustn't they blacken? 	mustn't I be blackening?
mustn't you be blackening?
mustn't she be blackening?
mustn't we be blackening?
mustn't you be blackening?
mustn't they be blackening? 	mustn't I have blackened?
mustn't you have blackened?
mustn't she have blackened?
mustn't we have blackened?
mustn't you have blackened?
mustn't they have blackened? 	mustn't I have been blackening?
mustn't you have been blackening?
mustn't she have been blackening?
mustn't we have been blackening?
mustn't you have been blackening?
mustn't they have been blackening?