What is the structure of the following sentence?
I need my history book back.
What is the grammatical role of the word "back"?
Put it down.
Hand it over.
Send it out.
I need it back.
These words indicate general direction, movement in space. I need you to return it to me. This history book must make a round-trip. I've handed it over to you and would like you to send it in the opposite direction.
She flew from London to New York and then she flew back.
Are you able to understand their function in the sentence without affixing a label to them?