figment of one's imagination vs invention

figment of one's imagination

noun
  • A product of the imagination. 

invention

noun
  • Something invented. 

  • The capacity to invent. 

  • The act of inventing. 

  • A small, self-contained composition, particularly those in J.S. Bach’s Two- and Three-part Inventions. 

How often have the words figment of one's imagination and invention occurred in a corpus of books? (source: Google Ngram Viewer )