English verb conjugation
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Regular verb: fester - festered - festered

Affirmation

Simple form	V-ing form
I must fester you must fester he must fester we must fester you must fester they must fester	I must be festering you must be festering he must be festering we must be festering you must be festering they must be festering
Perfect	V-ing perfect
I must have festered you must have festered he must have festered we must have festered you must have festered they must have festered	I must have been festering you must have been festering he must have been festering we must have been festering you must have been festering they must have been festering

Negation

Simple form	V-ing form
I mustn't fester you mustn't fester he mustn't fester we mustn't fester you mustn't fester they mustn't fester	I mustn't be festering you mustn't be festering he mustn't be festering we mustn't be festering you mustn't be festering they mustn't be festering
Perfect	V-ing perfect
I mustn't have festered you mustn't have festered he mustn't have festered we mustn't have festered you mustn't have festered they mustn't have festered	I mustn't have been festering you mustn't have been festering he mustn't have been festering we mustn't have been festering you mustn't have been festering they mustn't have been festering

Interrogative form

Simple form	V-ing form
must I fester? must you fester? must he fester? must we fester? must you fester? must they fester?	must I be festering? must you be festering? must he be festering? must we be festering? must you be festering? must they be festering?
Perfect	V-ing perfect
must I have festered? must you have festered? must he have festered? must we have festered? must you have festered? must they have festered?	must I have been festering? must you have been festering? must he have been festering? must we have been festering? must you have been festering? must they have been festering?

Interro-negative form

Simple form	V-ing form
mustn't I fester? mustn't you fester? mustn't he fester? mustn't we fester? mustn't you fester? mustn't they fester?	mustn't I be festering? mustn't you be festering? mustn't he be festering? mustn't we be festering? mustn't you be festering? mustn't they be festering?
Perfect	V-ing perfect
mustn't I have festered? mustn't you have festered? mustn't he have festered? mustn't we have festered? mustn't you have festered? mustn't they have festered?	mustn't I have been festering? mustn't you have been festering? mustn't he have been festering? mustn't we have been festering? mustn't you have been festering? mustn't they have been festering?