Firm Science SF

Firm Science Sci Fi is almost always crossing sub-genres because it can so easily be applied to them. In sci fi books are often categorized by how 'hard' or 'soft' they are, and Firm Science is the middle ground. Some describe the sub-genre as having a specific definition, but it kind of exists on a spectrum. The sub-genre tends to be very grounded in reality, and the world and people may seem even mundane, except for a few elements.

For example, faster-than-light travel or the ability to manipulate someone's dream—elements that are easy to accept for most readers, but not scientifically real, or at least not yet. Firm Science is a way to explore things that are absolutely possible and things that may be possible, but we simply don't know yet.

Other Features of Firm Science Science Fiction

Level of Real Science
High. Science and technology are very real, they are often described in technical terms. It all seems real, authentic and is never made to look silly—those pulpy ray guns have no place in Firm Science. Even when the known scientific laws are broken a rationale is provided.
Level of Grand Ideas/Social Implications
Variable. Firm Science is defined mostly by setting, so how grand the author wants to get while exploring ideas other than scientific ones is completely open. That being said, Firm Science almost always explores some big idea or social implication because why else would they include something that isn't strictly 'hard'? What happens when something like FTL travel revolutionizes transportation?
Level of Characterization
Variable. Again, because Firm Science is defined by setting how well an author develops a character is completely open.
Level of Plot Complexity
Variable. Interestingly, the plausible, but not too fantastic element of Firm Science tends to be a plot device. FTL has the potential to be a wonderful scientific achievement, but in Sci Fi it's just a way for an author to move the characters around without all the problems of taking hundreds of years to travel between solar systems and planets.
Level of Violence
Variable. Whatever the author wants the author can accomplish in Firm Science.

Related Science Fiction subgenres

Hard Science Fiction. Firm science has a bit of the Hard Sci Fi attitude.
Soft Science Fiction. Firm Science also has some of the Soft Sci Fi approach.
Science Fantasy. Sometimes the middle ground between 'hard' and 'soft' sci fi includes more fantastical elements—a mix of Hard sci fi and fantasy, which is okay too.
Nanopunk. Nano technology, at least in its 'wet' form is a technology that we're not sure can be possible yet, but it could be. So nanopunk is a kind of Firm Science.
AI Science Fiction. Non-biological intelligence may, or may not be possible—we're simply not sure right now, so much of AI sci fi is also Firm Science.

Popular Firm Science SF Books

1 Foundation

By Isaac Asimov. Some softer elements, like FTL and antigrav cars, but otherwise a rational series.
2 Giants

By James P. Hogan. This 5-novel series is noteworthy because of the history it establishes for the solar system and is a reaction to 2001: A Space Odyssey.
3 A Fire Upon the Deep

By Vernor Vinge. The first book in the Zones of Thought series and tells the tale of a galactic war. In the story the mind's potential is determined by its location in space.
4 Known Space

By Larry Niven. Niven's Known Space universe contains a hard science approach to science and the engineering of giant space structures, but does require unobtanium.
5 Starship Troopers

By Robert A. Heinlein. A vivid look at what it's like to be in a future military, starting from bootcamp. Definitely part of the Military Sci Fi sub-genre. The bugs are a bit silly, but there are some strong 'hard' elements that make up the story.
6 Forever War

By Joe Haldeman. The story of soldiers fighting an interstellar war against aliens. Includes some interesting fallout to relativistic travel and the result of time dilation.
7 The Golden Age

By John C. Wright This trilogy has some features of hard sci fi and uses nanotechnology well. It also depicts a far future society that is plausible. It is a more literary work than is typical of the sub-genre.
8 Schismatrix

By Bruce Sterling. While the avian-like aliens are implausible the story itself shows humanity moving in different directions, which is far more realistic than a uniform society often depicted in the softer sci fi.
9 Xeelee Sequence

By Stephen Baxter. A complictated sequence of stories and novels that span several billion years and includes the expansion of humanity and wars with aliens. The science is believable the world building is stellar.
10 The Black Cloud

By Fred Hoyle. This book incorporates many sciences in an encounter with an alien intelligence that takes the form of a cloud of gas.