gratification vs incentive

gratification

noun
  • A gratuity; a reward. 

  • The act of gratifying or pleasing, either the mind, or the appetite or taste. 

  • A feeling of pleasure; satisfaction. 

incentive

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

  • Something that motivates, rouses, or encourages. 

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

  • Serving to kindle or set on fire. 

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