Lester del Rey wrote, "Even the devoted aficionado or fan--has a hard time trying to explain what science fiction is," and no "full satisfactory definition" exists because "there are no easily delineated limits to science fiction."

Another definition is provided in The Literature Book by the publisher DK: "scenarios that are at the time of writing technologically impossible, extrapolating from present-day science...[,]...or that deal with some form of