In 1953, Isaac Asimov published an article titled "Social Science Fiction" in Modern Science Fiction. In that article he stated that every science fiction plot ultimately falls into one of three categories: Gadget, Adventure, or Social.
- Gadget: The focus of the story is the invention itself: How it comes to be invented, how it works, and/or what it is used for. The invention is the end result of the plot.
- Adventure: The invention is used as a dramatic prop. It may be the solution to a problem, or it may be causing the problem itself, but the main focus is on how the invention affects the events of the plot.
- Social: The focus of the story is on how the presence of the invention affects people's daily lives, whether for good or for ill. The chief distinction between this and the other two types is that the presence of the invention causes the plot rather than affecting it or being the goal.
To demonstrate what he meant by each, he used the example of three different late nineteenth century authors all being inspired to write new stories about the automobile, each going in one of three directions:
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, possibly beating a horse and carriage which have been challenged to a race. This is gadget science fiction. (Asimov, "Social 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 perfected 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. (ibid.)
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 travelers, cities have spread into the 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. (ibid.)
Or, to paraphrase it briefly:
Gadget sci-fi: Man invents car, holds lecture about his invention.
Prior to the rise of John W. Campbell and his Astounding Stories, the vast majority of science fiction fell under either Gadget or Adventure science fiction, with most of the characters being flat and stereotyped (though there were a few exceptions). Campbell wanted good stories, not merely good science; he wanted people to write science fiction that could stand on its own literary merits and seriously examine the consequences of technology on future society. His philosophy influenced authors such as Asimov and Robert A. Heinlein.
Most modern science fiction stories do not exist exclusively in any one category; they have elements of all three present to some degree or another. However, many clearly place more weight on one emphasis than the other two.
Note that this is not Mohs Scale of Science Fiction Hardness. That measures how well the main premise of the piece measures up to accepted real-world scientific theories; this categorizes a story on how it uses that premise. Also don't confuse this with Asimov's Three Laws of Robotics.
Please, No Examples, at least in the main page. However, feel free to list this on a work's trope page and discuss it there.