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