Lexicon: Science Fiction - Hard vs. Soft

Science Fiction Hard vs. Soft: all Science Fiction must have a sense of wonder, a what-if scenario, science, and the adventure of discovery. 

Hard Science Fiction: adheres firmly to the scientific method and the currently known rules of our universe. Science is about always asking questions and discarding disproven theories. This means that the science used is a true science – one that is defined by laws based on theory (if you drop an apple it falls because of gravity and you can calculate at what rate it falls by certain variables – etc).

Soft Science Fiction: Usually means that the story is not scientifically accurate. As is the right of all fiction writers the author took an idea not necessarily provable through science we have today and made it work in their world by sheer force of will. Some would also lump social sciences here. A social science is not easily defined by laws based on theory because culture and emotional mindset do not prove to always be the same.

Another way to look at it is: Hard Science Fiction focuses on the science (accuracy above all else, a glimpse of where science came from and especially where it is going). Soft Science Fiction focuses on people (how do humans usually interact with each other or other species, why do they react the same way or what causes the outcomes to be different).

Examples:

Hard Science Fiction: Twenty Thousand Leagues Under the Sea by Jules Verne, I, Robot by Isaac Asimov, and The Fountains of Paradise by Arthur C. Clark.

Soft Science Fiction: Ender’s Game by Orson Scott Card, Out of the Silent Planet by C.S. Lewis, and The Dispossessed by Ursula K. Le Guin.