English verb conjugation
MUST BACK

Regular verb: back - backed - backed

Affirmation

Simple form	V-ing form
I must back you must back he must back we must back you must back they must back	I must be backing you must be backing he must be backing we must be backing you must be backing they must be backing
Perfect	V-ing perfect
I must have backed you must have backed he must have backed we must have backed you must have backed they must have backed	I must have been backing you must have been backing he must have been backing we must have been backing you must have been backing they must have been backing

Negation

Simple form	V-ing form
I mustn't back you mustn't back he mustn't back we mustn't back you mustn't back they mustn't back	I mustn't be backing you mustn't be backing he mustn't be backing we mustn't be backing you mustn't be backing they mustn't be backing
Perfect	V-ing perfect
I mustn't have backed you mustn't have backed he mustn't have backed we mustn't have backed you mustn't have backed they mustn't have backed	I mustn't have been backing you mustn't have been backing he mustn't have been backing we mustn't have been backing you mustn't have been backing they mustn't have been backing

Interrogative form

Simple form	V-ing form
must I back? must you back? must he back? must we back? must you back? must they back?	must I be backing? must you be backing? must he be backing? must we be backing? must you be backing? must they be backing?
Perfect	V-ing perfect
must I have backed? must you have backed? must he have backed? must we have backed? must you have backed? must they have backed?	must I have been backing? must you have been backing? must he have been backing? must we have been backing? must you have been backing? must they have been backing?

Interro-negative form

Simple form	V-ing form
mustn't I back? mustn't you back? mustn't he back? mustn't we back? mustn't you back? mustn't they back?	mustn't I be backing? mustn't you be backing? mustn't he be backing? mustn't we be backing? mustn't you be backing? mustn't they be backing?
Perfect	V-ing perfect
mustn't I have backed? mustn't you have backed? mustn't he have backed? mustn't we have backed? mustn't you have backed? mustn't they have backed?	mustn't I have been backing? mustn't you have been backing? mustn't he have been backing? mustn't we have been backing? mustn't you have been backing? mustn't they have been backing?