could mass
Regular verb: mass - massed- massed

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

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

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

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