must understand
Irregular verb: understand - understood- understood

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I must understand
you must understand
he must understand
we must understand
you must understand
they must understand 	I must be understanding
you must be understanding
he must be understanding
we must be understanding
you must be understanding
they must be understanding	I must have understood
you must have understood
he must have understood
we must have understood
you must have understood
they must have understood	I must have been understanding
you must have been understanding
he must have been understanding
we must have been understanding
you must have been understanding
they must have been understanding	

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

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