The difference between fantasy and science fiction, syndicated from @nownovel

The following is syndicated from and is posted here with permission.
Articulating the difference between fantasy and science fiction can become surprisingly contentious as anyone who has witnessed furious debates about which books can enter science fiction awards can testify. However, there are a few key differences in the genres that can help us to separate one type of book from the other.

science fiction and fantasyWhy is it important to know whether your book is science fiction or fantasy? One of the most important reasons is for marketing purposes. Agents and publishers will want you to succinctly describe the genre your book fits into. In addition, while you are writing, you will likely find that characters seek different solutions and the overall plot will vary based on whether you are writing fantasy or science fiction.
  • Science fiction deals with scenarios and technology that are possible or may be possible based on science. Some science fiction such as far-future space opera or time travel stories may seem implausible, but they are still not beyond the realm of scientific theory. On the other hand, fantasy general deals with supernatural and magical occurrences that have no basis in science.
  • Fantasy is an older genre of literature than science fiction; in fact, fantasy is arguably the oldest genre. If we look back at the earliest surviving stories from human civilisation such as the Sumerian Epic of Gilgamesh or the ancient Greek myths, we find stories of gods, monsters and magic. Science fiction is a relatively recent genre of the last century or so with origins going back only a few hundred years before that.
  • Both science fiction and fantasy require rules. Just because fantasy is not based on scientific facts or speculation doesn’t mean that anything can go in fantasy. Certain laws must govern a fantasy world as well; the difference is that in fantasy, the author makes up the rules.
Surprisingly, science fiction and fantasy cannot always be distinguished by settings or other elements. Many would argue that Anne McCaffrey’s Pern series is science fiction despite the existence of dragons while others say the Star Wars films are clearly fantasy despite the space setting.
What do you feel is the the main difference between science fiction and fantasy?