Was this novel fantasy or science fiction? I distinguish the two like this. Both are speculative fiction. By speculative fiction I mean that the question is asked, what if ...? Fill in the elipsis with a fantastic premise. The answer to the question is the story itself. A fantastic premise is some proposition that is entirely outside the experience or likely experience of normal people. The word science in science fiction is not there for nothing. Science is the study of the real universe around us. That is, science is the study of reality itself. That means that if the fantastic premise is assumed, within the context of the story itself, to be a manifestation of reality then the story is science fiction. If the fantastic premise is assumed, within the context of the story itself, to be a manifestation of the supernatural then the story is a fantasy. That makes it real easy most of the time to tell the difference between a science fiction story and a fantasy. So, is Nine Princes in Amber a fantasy or a science fiction story? I don't know. It contains trophes that are usually associated with science fiction, trophes like parallel worlds. It contains trophes usually associated with fantasy like princes with extraordinary powers. The question is whether these powers are assumed, within the context of the story, to be manifestations of reality or of a supernatural nature. I can't quite figure it out. Are the parallel worlds manifestations of reality or are they fantasy lands? I don't know. When Corwin, the main character, escapes from his imprisonment it seems like a supernatural act to me, but is it really just a certain way of describing travel to a parallel world? Because of that scene in particular I am leaning toward saying that this is a fantasy, but I still remain unsure. If you have read the book I would be interested in your posting a comment saying which you think it is and why.