frankness vs illusion

frankness

noun
  • The state of being frank; candour; honesty. 

illusion

noun
  • A misapprehension; a belief in something that is in fact not true. 

  • Anything that seems to be something that it is not. 

  • A magician’s trick. 

  • The state of being deceived or misled. 

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