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There are a few ways to answer this. Which answer you use depends on what you want to achieve - something lacking in the original question. Does the work already exist and you're just trying to cat...
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#3: Attribution notice added
Source: https://writers.stackexchange.com/a/6341 License name: CC BY-SA 3.0 License URL: https://creativecommons.org/licenses/by-sa/3.0/
#2: Initial revision
There are a few ways to answer this. Which answer you use depends on what you want to achieve - something lacking in the original question. Does the work already exist and you're just trying to categorize it? Or are you in the planning stages? For this answer, I'm assuming that there are deities or other spiritual elements explicitly in your story. If there are deities: **Deities of any sort are fantasy, and we should all grow up and acknowledge this.** This is the prototypical hardline-atheist answer. Your book will be looked at as such. **Deities may seem unlikely, but what if "god" is really just a powerful energy being?** Arthur C. Clarke did this, as did Star Trek. It's a way to have gods in your fiction, still have it be science fiction (maybe), and avoid disrespecting religion. **"Pagan" gods are, of course, fantasy. The god I worship is real, so that makes this sci-fi.** That would make your book religious fiction. I'm not aware if religious science-fiction exists or not, so you'd either be joining an existing genre or creating a new one. If there are no deities, but there are spirits or ghosts, that would probably make your book a fantasy, or possibly what's now called a "paranormal" book.