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 must not stumble you must not stumble he must not stumble we must not stumble you must not stumble they must not stumble
V-ing form
I must not be stumbling you must not be stumbling he must not be stumbling we must not be stumbling you must not be stumbling they must not be stumbling
Perfect
I must not have stumbled you must not have stumbled he must not have stumbled we must not have stumbled you must not have stumbled they must not have stumbled
V-ing perfect
I must not have been stumbling you must not have been stumbling he must not have been stumbling we must not have been stumbling you must not have been stumbling they must not 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
must I not stumble? must you not stumble? must he not stumble? must we not stumble? must you not stumble? must they not stumble?
V-ing form
must I not be stumbling? must you not be stumbling? must he not be stumbling? must we not be stumbling? must you not be stumbling? must they not be stumbling?
Perfect
must I not have stumbled? must you not have stumbled? must he not have stumbled? must we not have stumbled? must you not have stumbled? must they not have stumbled?
V-ing perfect
must I not have been stumbling? must you not have been stumbling? must he not have been stumbling? must we not have been stumbling? must you not have been stumbling? must they not have been stumbling?