English verb conjugation
MUST UNDERUSE

Regular verb: underuse - underused - underused

Affirmation

Simple form	V-ing form
I must underuse you must underuse he must underuse we must underuse you must underuse they must underuse	I must be underusing you must be underusing he must be underusing we must be underusing you must be underusing they must be underusing
Perfect	V-ing perfect
I must have underused you must have underused he must have underused we must have underused you must have underused they must have underused	I must have been underusing you must have been underusing he must have been underusing we must have been underusing you must have been underusing they must have been underusing

Negation

Simple form	V-ing form
I mustn't underuse you mustn't underuse he mustn't underuse we mustn't underuse you mustn't underuse they mustn't underuse	I mustn't be underusing you mustn't be underusing he mustn't be underusing we mustn't be underusing you mustn't be underusing they mustn't be underusing
Perfect	V-ing perfect
I mustn't have underused you mustn't have underused he mustn't have underused we mustn't have underused you mustn't have underused they mustn't have underused	I mustn't have been underusing you mustn't have been underusing he mustn't have been underusing we mustn't have been underusing you mustn't have been underusing they mustn't have been underusing

Interrogative form

Simple form	V-ing form
must I underuse? must you underuse? must he underuse? must we underuse? must you underuse? must they underuse?	must I be underusing? must you be underusing? must he be underusing? must we be underusing? must you be underusing? must they be underusing?
Perfect	V-ing perfect
must I have underused? must you have underused? must he have underused? must we have underused? must you have underused? must they have underused?	must I have been underusing? must you have been underusing? must he have been underusing? must we have been underusing? must you have been underusing? must they have been underusing?

Interro-negative form

Simple form	V-ing form
mustn't I underuse? mustn't you underuse? mustn't he underuse? mustn't we underuse? mustn't you underuse? mustn't they underuse?	mustn't I be underusing? mustn't you be underusing? mustn't he be underusing? mustn't we be underusing? mustn't you be underusing? mustn't they be underusing?
Perfect	V-ing perfect
mustn't I have underused? mustn't you have underused? mustn't he have underused? mustn't we have underused? mustn't you have underused? mustn't they have underused?	mustn't I have been underusing? mustn't you have been underusing? mustn't he have been underusing? mustn't we have been underusing? mustn't you have been underusing? mustn't they have been underusing?