It's a reasonable divide. I'm wrapping up the Expanse series and I would consider it soft science fiction, veering into sci-fi. (mild spoiler? Maybe?) On one

It's a reasonable divide. I'm wrapping up the Expanse series and I would consider it soft science fiction, veering into sci-fi. (mild spoiler? Maybe?) On one hand, they have "epstein" drives which aren't FTL but constantly accelerate. Caring about gravity and physics is huge in the books, as are components of biology. On the other hand, the protomolecule and its associated story elements are all completely made up. There is no plausible explanation for its existence in our universe. The series is very much about humanity, the characters, and how the characters have developed in the incredible lifetime that occurs through the series. In that way, it is very much "Space Opera" and not sci-fi. But when I'm telling my friends what I'm reading, I don't want to explain "space opera" so I just say sci-fi. I guess I'm not helping. Likewise, Battlestar Galactica is definitely space fantasy (thanks season 4).