thought i was going to have to break out the "no true scotsman". hah.
there seems to be lots of blending. for instance, larry niven talks about the possibility of certain technologies and the consequences of using them. then some of his writing is problem solving and taking a logical argument to it's furthest extent. then some of it is full on space opera. which, at some levels is indistinguishable from fantasy. does any spec fic have aliens? sometimes, i think useful speculation may be hampered by "logical" assumptions made within a context populated by humans. john brunner wrote a book called "the crucible of time" in which, all of the characters are intelligent, insect aliens. this gives the first person narrative a truly alien feel. in some sense that is speculative, isn't it? WWAD what would aliens do? some very good sci-fi boils down to nothing more than a mystery story, dressed up in a grand future. Is mystery a type of speculation? robert reed wrote a book called "marrow" it is the far flung future for humanity, lots of interesting, crazy seeming technologies along the way, brilliant, i thought, but the main plot is simply a mystery story. it is one that takes place over thousands of years of the characters unusually long lifetimes, but still, a mystery story. lots of it based in pure speculation of, what if? i think i will have to further clarify my understanding here.