"Let us suppose it is 1880 and we have a series of three writers who are each interested in writing a story of the future about an imaginary vehicle that can move without horses by some internal source of power; a horseless carriage, in other words. We even make up a word and call it an automobile.
"Writer X spends most of his time describing how the machine would run, explaining the workings of an internal-combustion engine, painting a word-picture of the struggles of the inventor, who after numerous failures, comes up with a successful model. The climax of the yarn is the drama of the machine, chugging its way along at the gigantic speed of twenty miles an hour between a double crowd of cheering admirers, possibly beating a horse and carriage, which have been challenged to a race. This is gadget science fiction.
"Writer Y invents the automobile in a hurry, but now there is a gang of ruthless crooks intent on stealing this valuable invention. First they steal the inventor's beautiful daughter, whom they threaten with every dire eventuality but rape (in these adventure stories, girls exist to be rescued and have no other uses). The inventor's young assistant goes to the rescue. He can accomplish his purpose only by the use of the newly invented automobile. He dashes into the desert at an unheard of speed of twenty miles an hour to pick up the girl who otherwise would have died of thirst if he had relied on a horse, however rapid and sustained the horse's gallop. This is adventure science fiction.
"Writer Z has the automobile already perfected. A society exists in which it is already a problem. Because of the automobile a gigantic oil industry has grown up, highways have been paved across the nation, America has become a land of travellers, cities have spread out into suburbs, and what do we do about automobile accidents? Men, women, and children are being killed by automobiles faster than by artillery shells or airplane bombs. What can be done? What is the solution? This is social science fiction."