I think Dr. Willis McNelly at the California State University at Fullerton put it best when he said that the true protagonist of an sf story or novel is an idea and not a person. If it is *good* sf the idea is new, it is stimulating, and, probably most important of all, it sets off a chain-reaction of ramification-ideas in the mind of the reader; it so-to-speak unlocks the reader’s mind so that the mind, like the author’s, begins to create. Thus sf is creative and it inspires creativity, which mainstream fiction by-and-large does not do. We who read sf (I am speaking as a reader now, not a writer) read it because we love to experience this chain-reaction of ideas being set off in our minds by something we read, something with a new idea in it; hence the very best since fiction ultimately winds up being a collaboration between author and reader, in which both create and enjoy doing it: joy is the essential and final ingredient of science fiction, the joy of discovery of newness.