According to Wikipedia: Speculative fiction is a broad literary genre encompassing any fiction with supernatural, fantastical, or futuristic elements. This genre is usually attributed to Robert Heinlein, who coined it in 1947 in an editorial essay. Although there are instances of speculative fiction, or its variant ‘speculative literature’ being used before him, Robert Heinlein is, for a number of reasons, hailed as the father of speculative fiction.
I would go so far as to add, words that make you think about your world and a myriad of possibilities. This extra step encompasses alternative and hidden histories as well as lesser known belief systems, cultural “oddities”, and varied gender roles (and rules).
I’m not quite sure what fans of Lewis Carol and J.R.R. Tolkien feel about Robert Heinlein being the “father of speculative fiction” or of their work being put in the “instances of” box. I suppose it depends on your interpretation of the term. The Hobbit and all similar are generally labelled as high fantasy.
So what’s the difference you might ask? Speculative fiction is the umbrella term into which science fiction, fantasy (high or low), and horror sit. Robert Heinlein was mainly a science fiction writer, J.R.R. Tolkien was fantasy, and Stephen King is in the horror camp.
Annie Neugebauer has explored the term thoroughly in her blog post of the same name What is speculative fiction?
Each of the above categories come with their own sub-categories. For instance, low fantasy covers stories that are set in the real world but have “fantastical” elements (My novel, The Ouroboros Key fits this description) whereas high fantasy stories are set in completely fictional worlds and are dominated by the “fantastical” (The Hobbit, Lord of the Rings, The Chronicles of Thomas Covenant, and so on).
Game of Thrones belongs to the epic fantasy sub-genre, which includes real world settings with lots of high fantasy elements thrown in. To be classed as epic, the story must be complex and contain multiple plot lines (and lots of characters, and really really long).
Other fantasy sub-genres include alternate history and sword and sorcery. There’s an interesting exploration of the sub-genres on the Fantasy Faction website, and links to even more sub-genres (Steampunk, anyone?).
Science Fiction and Horror have their own ever-growing list of sub-genres as well. In Horror there is dark fantasy, supernatural, scifi horror, psychological, suspense/thriller… And in Science Fiction you can look forward to alien, space exploration, dystopia, utopia, alternate universe, and cyberpunk…
There is just not enough hours in the day, days in the year, or years in our lives to read all of the speculative fiction available!