ardor vs incentive

ardor

noun
  • Spirit; enthusiasm; passion. 

  • Intense heat. 

  • Great warmth of feeling; fervor; passion. 

incentive

noun
  • Something that motivates, rouses, or encourages. 

  • A bonus or reward, often monetary, to work harder. 

adj
  • Inciting; encouraging or moving; rousing to action; stimulating. 

  • Serving to kindle or set on fire. 

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