I must back you must back he must back we must back you must back they must back
Forma con V-ing
I must be backing you must be backing he must be backing we must be backing you must be backing they must be backing
Perfecto
I must have backed you must have backed he must have backed we must have backed you must have backed they must have backed
Perfecto con V-ing
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
Negación
Forma simple
I mustn't back you mustn't back he mustn't back we mustn't back you mustn't back they mustn't back
Forma con V-ing
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
Perfecto
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
Perfecto con V-ing
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
Forma interrogativa
Forma simple
must I back? must you back? must he back? must we back? must you back? must they back?
Forma con V-ing
must I be backing? must you be backing? must he be backing? must we be backing? must you be backing? must they be backing?
Perfecto
must I have backed? must you have backed? must he have backed? must we have backed? must you have backed? must they have backed?
Perfecto con V-ing
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?
Forma interro-negativa
Forma simple
mustn't I back? mustn't you back? mustn't he back? mustn't we back? mustn't you back? mustn't they back?
Forma con V-ing
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?
Perfecto
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?
Perfecto con V-ing
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?