At the top of the chart is the title: "Fantastic Fiction". Below, I have defined "fantastic fiction" as any story "in which the fictional world differs from ours in a radical and comprehensive way." That means you can't just throw in one talking animal and call the story fantasy -- unless it is suggested that talking animals are normal for your verse.
On the next level down, I have roughly defined the "Science Fiction" and "Fantasy" categories. In my conception, "Science Fiction" is the appropriate label for any fantastic story in which some attempt - however flawed - is made to rationally explain the other-worldly elements. These explanations, of course, exist on a sliding scale from "hard" (scientifically accurate) to "soft" (requires suspension of disbelief), but the explanation is still present or heavily implied. "Fantasy," on the other hand, is the appropriate label for any story that emphasizes "magic" or the irrational.
On the third level, we have our sub-categories. Beneath "Science Fiction," we have:
- Alternate History: Change one historical event and follow through on the consequences.
- Time Travel
- Future Projection: 1) Impact of new tech on society; 2) impact of sociological trends.
- Military: 1) Boot camp experiences; 2) hierarchy; 3) battle tech.
- Space-Based: Characters are either not on Earth or they leave Earth at some point.
- Epic Fantasy: 1) Quest; 2) clash of empires; 3) Lord of the Rings (as the exemplar)
- Contemporary, or "Urban," Fantasy: 1) Set in present day (usually); 2) monsters; 3) borrows from the horror genre
Of course, many works exist in the overlap between different categories, so in the above diagram, I have also started accounting for those. For instance, I have drawn a join between "Space-Based Science Fiction" and "Epic Fantasy" for "Space Opera" -- and I have stuck the Honorverse in the join between "Military Science Fiction" and "Space-Based Science Fiction." And if I were to try to classify, say, Larry Correia's Grimnoir series? I'd probably have to draw a big loop to join "Alternate History" with "Urban Fantasy." Whee!
So what do you guys think? Do you have your own mental flow-chart? Does it look anything like mine? Feel free to discuss your thoughts in the comments below!