cautionary tale vs fable

cautionary tale

noun
  • A story, originally told in folklore, to warn its audience of a certain danger. 

fable

noun
  • A fictitious narrative intended to enforce some useful truth or precept, usually with animals, etc. as characters; an apologue. Prototypically, Aesop's Fables. 

  • Fiction; untruth; falsehood. 

  • Any story told to excite wonder; common talk; the theme of talk. 

  • The plot, story, or connected series of events forming the subject of an epic or dramatic poem. 

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