Ralph Waldo Emerson

If you give me a typewriter and I'm having a good day, I can write a scene that will astonish its readers. That will perhaps make them laugh, perhaps make them cry - that will have some emotional clout to it. It doesn't cost much to do that.

The historical novelist has to consider what has actually happened, while the SF writer is dealing in possibilities, but they are both in the business of imagining a world unlike our own and yet connected to it.