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 must not lighten
you must not lighten
she must not lighten
we must not lighten
you must not lighten
they must not lighten 	I must not be lightening
you must not be lightening
she must not be lightening
we must not be lightening
you must not be lightening
they must not be lightening	I must not have lightened
you must not have lightened
she must not have lightened
we must not have lightened
you must not have lightened
they must not have lightened	I must not have been lightening
you must not have been lightening
she must not have been lightening
we must not have been lightening
you must not have been lightening
they must not 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 	
must I not lighten?
must you not lighten?
must she not lighten?
must we not lighten?
must you not lighten?
must they not lighten? 	must I not be lightening?
must you not be lightening?
must she not be lightening?
must we not be lightening?
must you not be lightening?
must they not be lightening? 	must I not have lightened?
must you not have lightened?
must she not have lightened?
must we not have lightened?
must you not have lightened?
must they not have lightened? 	must I not have been lightening?
must you not have been lightening?
must she not have been lightening?
must we not have been lightening?
must you not have been lightening?
must they not have been lightening?