I must guess you must guess she must guess we must guess you must guess they must guess
V-ing form
I must be guessing you must be guessing she must be guessing we must be guessing you must be guessing they must be guessing
Perfect
I must have guessed you must have guessed she must have guessed we must have guessed you must have guessed they must have guessed
V-ing perfect
I must have been guessing you must have been guessing she must have been guessing we must have been guessing you must have been guessing they must have been guessing
Negation
Simple form
I mustn't guess you mustn't guess she mustn't guess we mustn't guess you mustn't guess they mustn't guess
V-ing form
I mustn't be guessing you mustn't be guessing she mustn't be guessing we mustn't be guessing you mustn't be guessing they mustn't be guessing
Perfect
I mustn't have guessed you mustn't have guessed she mustn't have guessed we mustn't have guessed you mustn't have guessed they mustn't have guessed
V-ing perfect
I mustn't have been guessing you mustn't have been guessing she mustn't have been guessing we mustn't have been guessing you mustn't have been guessing they mustn't have been guessing
Interrogative form
Simple form
must I guess? must you guess? must she guess? must we guess? must you guess? must they guess?
V-ing form
must I be guessing? must you be guessing? must she be guessing? must we be guessing? must you be guessing? must they be guessing?
Perfect
must I have guessed? must you have guessed? must she have guessed? must we have guessed? must you have guessed? must they have guessed?
V-ing perfect
must I have been guessing? must you have been guessing? must she have been guessing? must we have been guessing? must you have been guessing? must they have been guessing?
Interro-negative form
Simple form
mustn't I guess? mustn't you guess? mustn't she guess? mustn't we guess? mustn't you guess? mustn't they guess?
V-ing form
mustn't I be guessing? mustn't you be guessing? mustn't she be guessing? mustn't we be guessing? mustn't you be guessing? mustn't they be guessing?
Perfect
mustn't I have guessed? mustn't you have guessed? mustn't she have guessed? mustn't we have guessed? mustn't you have guessed? mustn't they have guessed?
V-ing perfect
mustn't I have been guessing? mustn't you have been guessing? mustn't she have been guessing? mustn't we have been guessing? mustn't you have been guessing? mustn't they have been guessing?