English verb conjugation
MUST STIFF

Regular verb: stiff - stiffed - stiffed

Affirmation

Simple form	V-ing form
I must stiff you must stiff he must stiff we must stiff you must stiff they must stiff	I must be stiffing you must be stiffing he must be stiffing we must be stiffing you must be stiffing they must be stiffing
Perfect	V-ing perfect
I must have stiffed you must have stiffed he must have stiffed we must have stiffed you must have stiffed they must have stiffed	I must have been stiffing you must have been stiffing he must have been stiffing we must have been stiffing you must have been stiffing they must have been stiffing

Negation

Simple form	V-ing form
I mustn't stiff you mustn't stiff he mustn't stiff we mustn't stiff you mustn't stiff they mustn't stiff	I mustn't be stiffing you mustn't be stiffing he mustn't be stiffing we mustn't be stiffing you mustn't be stiffing they mustn't be stiffing
Perfect	V-ing perfect
I mustn't have stiffed you mustn't have stiffed he mustn't have stiffed we mustn't have stiffed you mustn't have stiffed they mustn't have stiffed	I mustn't have been stiffing you mustn't have been stiffing he mustn't have been stiffing we mustn't have been stiffing you mustn't have been stiffing they mustn't have been stiffing

Interrogative form

Simple form	V-ing form
must I stiff? must you stiff? must he stiff? must we stiff? must you stiff? must they stiff?	must I be stiffing? must you be stiffing? must he be stiffing? must we be stiffing? must you be stiffing? must they be stiffing?
Perfect	V-ing perfect
must I have stiffed? must you have stiffed? must he have stiffed? must we have stiffed? must you have stiffed? must they have stiffed?	must I have been stiffing? must you have been stiffing? must he have been stiffing? must we have been stiffing? must you have been stiffing? must they have been stiffing?

Interro-negative form

Simple form	V-ing form
mustn't I stiff? mustn't you stiff? mustn't he stiff? mustn't we stiff? mustn't you stiff? mustn't they stiff?	mustn't I be stiffing? mustn't you be stiffing? mustn't he be stiffing? mustn't we be stiffing? mustn't you be stiffing? mustn't they be stiffing?
Perfect	V-ing perfect
mustn't I have stiffed? mustn't you have stiffed? mustn't he have stiffed? mustn't we have stiffed? mustn't you have stiffed? mustn't they have stiffed?	mustn't I have been stiffing? mustn't you have been stiffing? mustn't he have been stiffing? mustn't we have been stiffing? mustn't you have been stiffing? mustn't they have been stiffing?