must lighten
Regular verb: lighten - lightened- lightened

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I must lighten
you must lighten
she must lighten
we must lighten
you must lighten
they must lighten 	I must be lightening
you must be lightening
she must be lightening
we must be lightening
you must be lightening
they must be lightening	I must have lightened
you must have lightened
she must have lightened
we must have lightened
you must have lightened
they must have lightened	I must have been lightening
you must have been lightening
she must have been lightening
we must have been lightening
you must have been lightening
they must have been lightening	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I mustn't lighten
you mustn't lighten
she mustn't lighten
we mustn't lighten
you mustn't lighten
they mustn't lighten 	I mustn't be lightening
you mustn't be lightening
she mustn't be lightening
we mustn't be lightening
you mustn't be lightening
they mustn't be lightening	I mustn't have lightened
you mustn't have lightened
she mustn't have lightened
we mustn't have lightened
you mustn't have lightened
they mustn't have lightened	I mustn't have been lightening
you mustn't have been lightening
she mustn't have been lightening
we mustn't have been lightening
you mustn't have been lightening
they mustn't have been lightening	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
must I lighten?
must you lighten?
must she lighten?
must we lighten?
must you lighten?
must they lighten? 	must I be lightening?
must you be lightening?
must she be lightening?
must we be lightening?
must you be lightening?
must they be lightening? 	must I have lightened?
must you have lightened?
must she have lightened?
must we have lightened?
must you have lightened?
must they have lightened? 	must I have been lightening?
must you have been lightening?
must she have been lightening?
must we have been lightening?
must you have been lightening?
must they have been lightening? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
mustn't I lighten?
mustn't you lighten?
mustn't she lighten?
mustn't we lighten?
mustn't you lighten?
mustn't they lighten? 	mustn't I be lightening?
mustn't you be lightening?
mustn't she be lightening?
mustn't we be lightening?
mustn't you be lightening?
mustn't they be lightening? 	mustn't I have lightened?
mustn't you have lightened?
mustn't she have lightened?
mustn't we have lightened?
mustn't you have lightened?
mustn't they have lightened? 	mustn't I have been lightening?
mustn't you have been lightening?
mustn't she have been lightening?
mustn't we have been lightening?
mustn't you have been lightening?
mustn't they have been lightening?