again vs back and forth

again

adv
  • Back (to a former place or state). 

  • Another time; once more. 

  • I ask again, I say again; used in repeating a question or statement. 

  • Over and above a factor of one. 

  • Moreover; besides; further. 

  • Here too, here also, in this case as well; used in applying a previously made point to a new instance; sometimes preceded by "here". 

  • Tell me again, say again; used in asking a question to which one may have already received an answer that one cannot remember. 

  • Used metalinguistically, with the repetition being in the discussion, or in the linguistic or pragmatic context of the discussion, rather than in the subject of discussion. 

back and forth

adv
  • From one place to another and back again. 

noun
  • Negotiations or discussions between two or more parties, a dialog. 

  • The movement (of someone or something) forward followed by a return to the same position. May refer to a concept such as an emotional state or a relationship as well as a physical thing. 

adj
  • Going from one place or position to another and back again. 

How often have the words again and back and forth occurred in a corpus of books? (source: Google Ngram Viewer )