"When asked to "define the difference between fantasy and science fiction," I mouth and mumble and always end up talking about the spectrum, that very useful spectrum, along which one thing shades into another. Definitions are for grammar, not literature, I say, and boxes are for bones. But of course fantasy and science fiction different, just as red and blue are different; they have different frequencies; if you mix them (on paper--I work on paper) you get purple, something else again."