I must understand you must understand she must understand we must understand you must understand they must understand
V-ing form
I must be understanding you must be understanding she must be understanding we must be understanding you must be understanding they must be understanding
Perfect
I must have understood you must have understood she must have understood we must have understood you must have understood they must have understood
V-ing perfect
I must have been understanding you must have been understanding she must have been understanding we must have been understanding you must have been understanding they must have been understanding
Negation
Simple form
I must not understand you must not understand she must not understand we must not understand you must not understand they must not understand
V-ing form
I must not be understanding you must not be understanding she must not be understanding we must not be understanding you must not be understanding they must not be understanding
Perfect
I must not have understood you must not have understood she must not have understood we must not have understood you must not have understood they must not have understood
V-ing perfect
I must not have been understanding you must not have been understanding she must not have been understanding we must not have been understanding you must not have been understanding they must not have been understanding
Interrogative form
Simple form
must I understand? must you understand? must she understand? must we understand? must you understand? must they understand?
V-ing form
must I be understanding? must you be understanding? must she be understanding? must we be understanding? must you be understanding? must they be understanding?
Perfect
must I have understood? must you have understood? must she have understood? must we have understood? must you have understood? must they have understood?
V-ing perfect
must I have been understanding? must you have been understanding? must she have been understanding? must we have been understanding? must you have been understanding? must they have been understanding?
Interro-negative form
Simple form
must I not understand? must you not understand? must she not understand? must we not understand? must you not understand? must they not understand?
V-ing form
must I not be understanding? must you not be understanding? must she not be understanding? must we not be understanding? must you not be understanding? must they not be understanding?
Perfect
must I not have understood? must you not have understood? must she not have understood? must we not have understood? must you not have understood? must they not have understood?
V-ing perfect
must I not have been understanding? must you not have been understanding? must she not have been understanding? must we not have been understanding? must you not have been understanding? must they not have been understanding?