I must underestimate you must underestimate he must underestimate we must underestimate you must underestimate they must underestimate
V-ing form
I must be underestimating you must be underestimating he must be underestimating we must be underestimating you must be underestimating they must be underestimating
Perfect
I must have underestimated you must have underestimated he must have underestimated we must have underestimated you must have underestimated they must have underestimated
V-ing perfect
I must have been underestimating you must have been underestimating he must have been underestimating we must have been underestimating you must have been underestimating they must have been underestimating
Negation
Simple form
I mustn't underestimate you mustn't underestimate he mustn't underestimate we mustn't underestimate you mustn't underestimate they mustn't underestimate
V-ing form
I mustn't be underestimating you mustn't be underestimating he mustn't be underestimating we mustn't be underestimating you mustn't be underestimating they mustn't be underestimating
Perfect
I mustn't have underestimated you mustn't have underestimated he mustn't have underestimated we mustn't have underestimated you mustn't have underestimated they mustn't have underestimated
V-ing perfect
I mustn't have been underestimating you mustn't have been underestimating he mustn't have been underestimating we mustn't have been underestimating you mustn't have been underestimating they mustn't have been underestimating
Interrogative form
Simple form
must I underestimate? must you underestimate? must he underestimate? must we underestimate? must you underestimate? must they underestimate?
V-ing form
must I be underestimating? must you be underestimating? must he be underestimating? must we be underestimating? must you be underestimating? must they be underestimating?
Perfect
must I have underestimated? must you have underestimated? must he have underestimated? must we have underestimated? must you have underestimated? must they have underestimated?
V-ing perfect
must I have been underestimating? must you have been underestimating? must he have been underestimating? must we have been underestimating? must you have been underestimating? must they have been underestimating?
Interro-negative form
Simple form
mustn't I underestimate? mustn't you underestimate? mustn't he underestimate? mustn't we underestimate? mustn't you underestimate? mustn't they underestimate?
V-ing form
mustn't I be underestimating? mustn't you be underestimating? mustn't he be underestimating? mustn't we be underestimating? mustn't you be underestimating? mustn't they be underestimating?
Perfect
mustn't I have underestimated? mustn't you have underestimated? mustn't he have underestimated? mustn't we have underestimated? mustn't you have underestimated? mustn't they have underestimated?
V-ing perfect
mustn't I have been underestimating? mustn't you have been underestimating? mustn't he have been underestimating? mustn't we have been underestimating? mustn't you have been underestimating? mustn't they have been underestimating?