must muff
Regular verb: muff - muffed- muffed

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I must muff
you must muff
he must muff
we must muff
you must muff
they must muff 	I must be muffing
you must be muffing
he must be muffing
we must be muffing
you must be muffing
they must be muffing	I must have muffed
you must have muffed
he must have muffed
we must have muffed
you must have muffed
they must have muffed	I must have been muffing
you must have been muffing
he must have been muffing
we must have been muffing
you must have been muffing
they must have been muffing	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I mustn't muff
you mustn't muff
he mustn't muff
we mustn't muff
you mustn't muff
they mustn't muff 	I mustn't be muffing
you mustn't be muffing
he mustn't be muffing
we mustn't be muffing
you mustn't be muffing
they mustn't be muffing	I mustn't have muffed
you mustn't have muffed
he mustn't have muffed
we mustn't have muffed
you mustn't have muffed
they mustn't have muffed	I mustn't have been muffing
you mustn't have been muffing
he mustn't have been muffing
we mustn't have been muffing
you mustn't have been muffing
they mustn't have been muffing	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
must I muff?
must you muff?
must he muff?
must we muff?
must you muff?
must they muff? 	must I be muffing?
must you be muffing?
must he be muffing?
must we be muffing?
must you be muffing?
must they be muffing? 	must I have muffed?
must you have muffed?
must he have muffed?
must we have muffed?
must you have muffed?
must they have muffed? 	must I have been muffing?
must you have been muffing?
must he have been muffing?
must we have been muffing?
must you have been muffing?
must they have been muffing? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
mustn't I muff?
mustn't you muff?
mustn't he muff?
mustn't we muff?
mustn't you muff?
mustn't they muff? 	mustn't I be muffing?
mustn't you be muffing?
mustn't he be muffing?
mustn't we be muffing?
mustn't you be muffing?
mustn't they be muffing? 	mustn't I have muffed?
mustn't you have muffed?
mustn't he have muffed?
mustn't we have muffed?
mustn't you have muffed?
mustn't they have muffed? 	mustn't I have been muffing?
mustn't you have been muffing?
mustn't he have been muffing?
mustn't we have been muffing?
mustn't you have been muffing?
mustn't they have been muffing?