must mass
Regular verb: mass - massed- massed

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I must mass
you must mass
he must mass
we must mass
you must mass
they must mass 	I must be massing
you must be massing
he must be massing
we must be massing
you must be massing
they must be massing	I must have massed
you must have massed
he must have massed
we must have massed
you must have massed
they must have massed	I must have been massing
you must have been massing
he must have been massing
we must have been massing
you must have been massing
they must have been massing	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I mustn't mass
you mustn't mass
he mustn't mass
we mustn't mass
you mustn't mass
they mustn't mass 	I mustn't be massing
you mustn't be massing
he mustn't be massing
we mustn't be massing
you mustn't be massing
they mustn't be massing	I mustn't have massed
you mustn't have massed
he mustn't have massed
we mustn't have massed
you mustn't have massed
they mustn't have massed	I mustn't have been massing
you mustn't have been massing
he mustn't have been massing
we mustn't have been massing
you mustn't have been massing
they mustn't have been massing	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
must I mass?
must you mass?
must he mass?
must we mass?
must you mass?
must they mass? 	must I be massing?
must you be massing?
must he be massing?
must we be massing?
must you be massing?
must they be massing? 	must I have massed?
must you have massed?
must he have massed?
must we have massed?
must you have massed?
must they have massed? 	must I have been massing?
must you have been massing?
must he have been massing?
must we have been massing?
must you have been massing?
must they have been massing? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
mustn't I mass?
mustn't you mass?
mustn't he mass?
mustn't we mass?
mustn't you mass?
mustn't they mass? 	mustn't I be massing?
mustn't you be massing?
mustn't he be massing?
mustn't we be massing?
mustn't you be massing?
mustn't they be massing? 	mustn't I have massed?
mustn't you have massed?
mustn't he have massed?
mustn't we have massed?
mustn't you have massed?
mustn't they have massed? 	mustn't I have been massing?
mustn't you have been massing?
mustn't he have been massing?
mustn't we have been massing?
mustn't you have been massing?
mustn't they have been massing?