In soft science fiction the science is only peripheral to the story - it provides the scenery and backdrops that help us to recognize it when we see it.

Take any western, war story, romance, mystery, etc., and set it on Mars, on a space ship or space station, into the future or distant past, or on a planet in a galaxy far, far away, and it is soft science fiction.

You recognize it as science fiction because of the setting.

Look at the cover art of "The Magazine of Fantasy and Science Fiction" pictured at the right.  In the 30s and 40s, nearly naked people on the cover was a dead giveaway that you were looking at a science fiction magazine.  Not so today.  It's pretty obvious that the story involves some sort of clandestine romance, but you can also recognize that it's science fiction just by looking at their vehicles.  The vehicles, or science in general, may have no major role in the story.  Still, it's science fiction - you know it when you see it; it's soft science fiction.