Card points out that science fiction is really one of two subcategories, the other being "fantasy," of what he refers to as "speculative fiction."

"Speculative fiction" includes stories that take place in a setting contrary to reality. For instance, the following settings would be indicative of speculative fiction -

     the future

     the past when it contradicts the known facts of history (such as a story in which Hitler doesn't die and Germany wins World War II).

     other worlds than Earth

     Pre-historic Earth when the known archeological record is contradicted (such as stories about lost civilizations or ancient aliens).

     But speculative fiction can be set in the present on Earth.  When Jules Verne and H. G. Wells wrote their science fiction stories, the stories took place on the Earth of their present.  One of my favorite science fiction stories, "Flowers for Algernon" (which was made into the movie, "Charly") takes place in a very contemporary setting on Earth.