English verb conjugation
MUST ERR

Regular verb: err - erred - erred

Affirmation

Simple form	V-ing form
I must err you must err he must err we must err you must err they must err	I must be erring you must be erring he must be erring we must be erring you must be erring they must be erring
Perfect	V-ing perfect
I must have erred you must have erred he must have erred we must have erred you must have erred they must have erred	I must have been erring you must have been erring he must have been erring we must have been erring you must have been erring they must have been erring

Negation

Simple form	V-ing form
I mustn't err you mustn't err he mustn't err we mustn't err you mustn't err they mustn't err	I mustn't be erring you mustn't be erring he mustn't be erring we mustn't be erring you mustn't be erring they mustn't be erring
Perfect	V-ing perfect
I mustn't have erred you mustn't have erred he mustn't have erred we mustn't have erred you mustn't have erred they mustn't have erred	I mustn't have been erring you mustn't have been erring he mustn't have been erring we mustn't have been erring you mustn't have been erring they mustn't have been erring

Interrogative form

Simple form	V-ing form
must I err? must you err? must he err? must we err? must you err? must they err?	must I be erring? must you be erring? must he be erring? must we be erring? must you be erring? must they be erring?
Perfect	V-ing perfect
must I have erred? must you have erred? must he have erred? must we have erred? must you have erred? must they have erred?	must I have been erring? must you have been erring? must he have been erring? must we have been erring? must you have been erring? must they have been erring?

Interro-negative form

Simple form	V-ing form
mustn't I err? mustn't you err? mustn't he err? mustn't we err? mustn't you err? mustn't they err?	mustn't I be erring? mustn't you be erring? mustn't he be erring? mustn't we be erring? mustn't you be erring? mustn't they be erring?
Perfect	V-ing perfect
mustn't I have erred? mustn't you have erred? mustn't he have erred? mustn't we have erred? mustn't you have erred? mustn't they have erred?	mustn't I have been erring? mustn't you have been erring? mustn't he have been erring? mustn't we have been erring? mustn't you have been erring? mustn't they have been erring?