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