inflexibleness vs obstinacy

inflexibleness

noun
  • Obstinacy of will or temper; firmness of purpose that will not yield to importunity or persuasion; unbending pertinacity. 

  • The quality or state of being inflexible 

obstinacy

noun
  • The state, or an act, of stubbornness or doggedness. 

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