I must perk you must perk he must perk we must perk you must perk they must perk
V-ing form
I must be perking you must be perking he must be perking we must be perking you must be perking they must be perking
Perfect
I must have perked you must have perked he must have perked we must have perked you must have perked they must have perked
V-ing perfect
I must have been perking you must have been perking he must have been perking we must have been perking you must have been perking they must have been perking
Negation
Simple form
I mustn't perk you mustn't perk he mustn't perk we mustn't perk you mustn't perk they mustn't perk
V-ing form
I mustn't be perking you mustn't be perking he mustn't be perking we mustn't be perking you mustn't be perking they mustn't be perking
Perfect
I mustn't have perked you mustn't have perked he mustn't have perked we mustn't have perked you mustn't have perked they mustn't have perked
V-ing perfect
I mustn't have been perking you mustn't have been perking he mustn't have been perking we mustn't have been perking you mustn't have been perking they mustn't have been perking
Interrogative form
Simple form
must I perk? must you perk? must he perk? must we perk? must you perk? must they perk?
V-ing form
must I be perking? must you be perking? must he be perking? must we be perking? must you be perking? must they be perking?
Perfect
must I have perked? must you have perked? must he have perked? must we have perked? must you have perked? must they have perked?
V-ing perfect
must I have been perking? must you have been perking? must he have been perking? must we have been perking? must you have been perking? must they have been perking?
Interro-negative form
Simple form
mustn't I perk? mustn't you perk? mustn't he perk? mustn't we perk? mustn't you perk? mustn't they perk?
V-ing form
mustn't I be perking? mustn't you be perking? mustn't he be perking? mustn't we be perking? mustn't you be perking? mustn't they be perking?
Perfect
mustn't I have perked? mustn't you have perked? mustn't he have perked? mustn't we have perked? mustn't you have perked? mustn't they have perked?
V-ing perfect
mustn't I have been perking? mustn't you have been perking? mustn't he have been perking? mustn't we have been perking? mustn't you have been perking? mustn't they have been perking?