raison d'être vs reasoning

raison d'être

noun
  • Reason for being. The claimed reason for the existence of something or someone; the sole or ultimate purpose of something or someone. 

reasoning

noun
  • The deduction of inferences or interpretations from premises, abstract thought, ratiocination; (countable) any instance of this, especially as a process leading to an action, motive. 

  • A Rastafari meeting held for the purposes of chanting, prayer and discussion. 

How often have the words raison d'être and reasoning occurred in a corpus of books? (source: Google Ngram Viewer )