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 cannot back you cannot back he cannot back we cannot back you cannot back they cannot back	I cannot be backing you cannot be backing he cannot be backing we cannot be backing you cannot be backing they cannot be backing
Perfect	V-ing perfect
I cannot have backed you cannot have backed he cannot have backed we cannot have backed you cannot have backed they cannot have backed	I cannot have been backing you cannot have been backing he cannot have been backing we cannot have been backing you cannot have been backing they cannot 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 I not back? can you not back? can he not back? can we not back? can you not back? can they not back?	can I not be backing? can you not be backing? can he not be backing? can we not be backing? can you not be backing? can they not be backing?
Perfect	V-ing perfect
can I not have backed? can you not have backed? can he not have backed? can we not have backed? can you not have backed? can they not have backed?	can I not have been backing? can you not have been backing? can he not have been backing? can we not have been backing? can you not have been backing? can they not have been backing?