English verb conjugation
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Regular verb: fester - festered - festered

Affirmation

Simple form	V-ing form
I must fester you must fester she must fester we must fester you must fester they must fester	I must be festering you must be festering she 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 she 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 she 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 she 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 she 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 she 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 she 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 she fester? must we fester? must you fester? must they fester?	must I be festering? must you be festering? must she 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 she 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 she 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 she 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 she 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 she 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 she have been festering? mustn't we have been festering? mustn't you have been festering? mustn't they have been festering?