English verb conjugation
MUST BACK

Regular verb: back - backed - backed

Affirmation

Simple form	V-ing form
I must back you must back she must back we must back you must back they must back	I must be backing you must be backing she 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 she 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 she 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 she 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 she 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 she 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 she 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 she back? must we back? must you back? must they back?	must I be backing? must you be backing? must she 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 she 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 she 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 she 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 she 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 she 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 she have been backing? mustn't we have been backing? mustn't you have been backing? mustn't they have been backing?