science fiction vs speculative fiction

science fiction

noun
  • Fiction in which advanced technology or science is a key element. 

  • Technology that, while theoretically possible, is not yet practical. 

speculative fiction

noun
  • A class of fiction involving fantastic, supernatural or futuristic elements, including fantasy, horror, and science fiction, dealing with worlds, themes, and characters not part of everyday life. 

  • A particular work belonging to this class. 

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