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