Science fiction is difficult to define, as it includes a wide range of
Hugo Gernsback, who suggested the term "scientifiction" for his
Amazing Stories magazine, wrote: "By 'scientifiction' I mean the
H. G. Wells and
Edgar Allan Poe type of story—a charming romance intermingled with scientific fact and prophetic vision... Not only do these amazing tales make tremendously interesting reading—they are always instructive. They supply knowledge... in a very palatable form... New adventures pictured for us in the scientifiction of today are not at all impossible of realization tomorrow... Many great science stories destined to be of historical interest are still to be written... Posterity will point to them as having blazed a new trail, not only in literature and fiction, but progress as well."
James Blish wrote about the English term "science fiction": "Wells used the term originally to cover what we would today call ‘hard’ science fiction, in which a conscientious attempt to be faithful to already known facts (as of the date of writing) was the substrate on which the story was to be built, and if the story was also to contain a miracle, it ought at least not to contain a whole arsenal of them."
Rod Serling said, "fantasy is the impossible made probable. Science fiction is the improbable made possible."
Isaac Asimov said: "Science fiction can be defined as that branch of literature which deals with the reaction of human beings to changes in science and technology."
 According to
Robert A. Heinlein, "a handy short definition of almost all science fiction might read: realistic speculation about possible future events, based solidly on adequate knowledge of the real world, past and present, and on a thorough understanding of the nature and significance of the
Lester del Rey wrote, "Even the devoted aficionado—or fan—has a hard time trying to explain what science fiction is", and that the reason for there not being a "full satisfactory definition" is that "there are no easily delineated limits to science fiction."
 Author and editor
Damon Knight summed up the difficulty, saying "science fiction is what we point to when we say it",
 while author Mark C. Glassy argues that the definition of science fiction is like the definition of pornography: you do not know what it is, but
you know it when you see it.