English verb conjugation
CAN BACK

Regular verb: back - backed - backed

Affirmation

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

Negation

Simple form	V-ing form
I can't back you can't back he can't back we can't back you can't back they can't back	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
Perfect	V-ing perfect
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	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

Interrogative form

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

Interro-negative form

Simple form	V-ing form
can't I back? can't you back? can't he back? can't we back? can't you back? can't they back?	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?
Perfect	V-ing perfect
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?	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?