I can fester you can fester he can fester we can fester you can fester they can fester
V-ing form
I can be festering you can be festering he can be festering we can be festering you can be festering they can be festering
Perfect
I can have festered you can have festered he can have festered we can have festered you can have festered they can have festered
V-ing perfect
I can have been festering you can have been festering he can have been festering we can have been festering you can have been festering they can have been festering
Negation
Simple form
I cannot fester you cannot fester he cannot fester we cannot fester you cannot fester they cannot fester
V-ing form
I cannot be festering you cannot be festering he cannot be festering we cannot be festering you cannot be festering they cannot be festering
Perfect
I cannot have festered you cannot have festered he cannot have festered we cannot have festered you cannot have festered they cannot have festered
V-ing perfect
I cannot have been festering you cannot have been festering he cannot have been festering we cannot have been festering you cannot have been festering they cannot have been festering
Interrogative form
Simple form
can I fester? can you fester? can he fester? can we fester? can you fester? can they fester?
V-ing form
can I be festering? can you be festering? can he be festering? can we be festering? can you be festering? can they be festering?
Perfect
can I have festered? can you have festered? can he have festered? can we have festered? can you have festered? can they have festered?
V-ing perfect
can I have been festering? can you have been festering? can he have been festering? can we have been festering? can you have been festering? can they have been festering?
Interro-negative form
Simple form
can I not fester? can you not fester? can he not fester? can we not fester? can you not fester? can they not fester?
V-ing form
can I not be festering? can you not be festering? can he not be festering? can we not be festering? can you not be festering? can they not be festering?
Perfect
can I not have festered? can you not have festered? can he not have festered? can we not have festered? can you not have festered? can they not have festered?
V-ing perfect
can I not have been festering? can you not have been festering? can he not have been festering? can we not have been festering? can you not have been festering? can they not have been festering?