What are the motifs in Science Fiction and Fantasy Literature by ?

Salvation and destruction are recurring ideas in science fiction. From the very beginning of Science Fiction, most writers have expressed one of two diametrically opposed ideas concerning the development of science and technology—it will save humanity or it will destroy it. Many of the works that have received favorable criticism or which reign as "classics" fall into the latter group. Perhaps it is because of their darker qualities that these works stand out from the others; Science Fiction has always been strongest when it issues warnings. Readers need look no further than Verne and Wells. Verne's "Extraordinary Journeys" novels tell predominantly positive tales about man's use of the machine to explore and conquer the unknown.