"Science fiction" is difficult to define precisely, as it includes a wide range of concepts and themes. American science fiction and fantasy writer James Blish wrote: "Wells used the term originally to cover what we would today call "hard" science fiction, in which a conscientious attempt to be faithful to already known facts (as of the date of writing) was the substrate on which the story was to be built, and if the story was also to contain a miracle, it ought at least not to contain a whole arsenal of them."[4]