When I was in high school, my English teachers all defined science fiction by three story types: space exploration, utopian society, post-nuclear winter. When I started writing…it became clear very quickly that science fiction is a lot more diverse, and therefore a lot more complicated.
At its core, all science fiction is driven by science. If some aspect of science is the key to the plot, then the story most likely can be classified as science fiction.
When your basic genre definition is so wide open, there is a lot of room to maneuver and tell an interesting science fiction story. You can focus on technology and its impact on relations between countries, and you’ve got yourself a thrilling military science fiction. You can go a more traditional route and send out explorers across the galaxy in search of aliens, elements and material, or just a new life where you get to focus on the nitty-gritty details of how the characters live on their new home planet.
Of course, there are the problem children. Hard science fiction, so often defined as stories driven by strong plot elements rooted in the applied sciences, is pretty easy to recognize as science fiction. But the social sciences, when they become the driving force of the plot, create soft science fiction. (Want some fun? Listen to a debate between writers of hard and soft science fiction. It gets a little crazy.) And then of course there’s steampunk, which will come back up in future posts because it’s such a contested subgenre.
The bottom line is: If your story would appeal to the STEM (science, technology, engineering, math) crowd, and you’re looking to playing with extending theories and concepts, there’s a good chance you’re playing within the realm of science fiction.