Science fiction is the search for definition of man and his status in the universe which will stand in our advanced but confused state of knowledge (science), and is characteristically cast in the Gothic or post-Gothic mould.
Trillion Year Spree: the History of Science Fiction (London, 1986)
The future depicted in a good SF story ought to be in fact possible, or at least plausible. That means that the writer should be able to convince the reader (and himself) that the wonders he is describing really can come true...and that gets tricky when you take a good, hard look at the world around you.
The Shape of Things to Come and Why It Is Bad, SFC, December 1991
Definitions of Science Fiction
Sci-fi authors define sci-fi October 23, 2009 Science Fiction
I'll quote myself here: “Though important events, situations and characters may in themselves be fantastical, science fiction assumes an explanation based on a logical universe. This is opposed to fantasy works, and some horror, in which such ideas are described through magic or the whims of the gods.”
A unit on genetics had Sephali Ray’s students jazzed. A seventh-grade science teacher at the New York City Lab School, a public middle- and high-school, Ray didn't stop with the scientific facts. “It’s absurd for students to talk about how DNA works without trying to understand its implications for society,” says Ray.
Good science fiction is story, science, and speculation all wrapped up in a package custom-made for improving literacy and critical-thinking skills-it does not get more convenient.
Students prepare by analyzing a work of science fiction and examining the underlying science idea in terms of the attitude and knowledge conveyed through the story about the author, following this with research on the author.
October 23, 2009 Science Fiction Every Sunday our characters talk about a book they've read in full-page full-color comic strips. Our book clubs are posted in libraries, book stores, and in homes, and you have our permission to do so too ( write us if you're interested in other uses).
SF Site is composed of many pieces. Twice a month since July 1997, we have posted a mixture of book reviews, opinion pieces, author interviews, fiction excerpts, author and publisher reading lists and a variety of other features. At the same time, we've maintained a comprehensive list of links to author and fan tribute sites, SF conventions, SF TV and movies, magazines and e-zines, writer resources, publishers and small press sites and many other SF resources.
The Hugo Award was named in honor of Hugo Gernsback, “The Father of Magazine Science Fiction,” as he was described in a special award given to him in 1960. The Hugo Award, also known as the Science Fiction Achievement Award, is given annually by the World Science Fiction Society (WSFS) . The distinguishing characteristics of the Hugo Award are that it is sponsored by WSFS, administered by the committee of the World Science Fiction Convention (Worldcon) held that year, and determined by nominations from and a popular vote of the membership of WSFS.
In general, science fiction is the literature of things that might someday be possible, and fantasy is the literature of things that are inherently impossible.  Magic and mythology are popular themes in fantasy .  Some narratives are described as being essentially science fiction but “with fantasy elements”. The term " science fantasy " is sometimes used to describe such material. 
Science fiction from Wikipedia, the free encyclopedia
If anyone were to force me to make a thumbnail description of the differences between SF and fantasy, I think I would say that SF looks towards an imaginary future, while fantasy, by and large, looks towards an imaginary past. Both can be entertaining. Both can possibly be, perhaps sometimes actually are, even inspiring. But as we can't change the past, and can't avoid changing the future, only one of them can be real.
Star Wars could be considered both science fantasy and standard science fiction
A definition, offered by Rod Serling , is that "science fiction makes the implausible possible, while science fantasy makes the impossible plausible." The meaning is that science fiction describes unlikely things that could possibly take place in the real world under certain conditions, while science fantasy gives a veneer of realism to things that simply could not happen in the real world under any circumstances. Another interpretation is that science fiction does not permit the existence of supernatural elements; science fantasy does.
Wikipedia (an article that “ has multiple issues.”)