- From the consumer’s perspective, fantasy, hard SF and soft SF are labels; like most labels, they’re only useless if there’s a common standard, or if they communicate something to the person using the label.
- There’s probably a rigorous definition for these terms in the academic literary community, but it’s probably confined there.
- The publishing community tends to use the more practical approach of division-by-author e.g. “it’s by author X, therefore it’s hard SF”.
- Most people use the labels as shorthand for “things I like” and “things I don’t like”. That’s probably the most useful to the person doing the labeling; isn’t the point to enjoy the time you spend reading?

Adopting that viewpoint tends to mean that the discussion is pointless, and what fun would that be? :<)

Anyway, I disagree that “hard SF is where the imagination is”; hard SF is where the science is. Hard SF, as you noted, tends to explore the implications of an idea in greater depth, and extrapolate from that idea to build the world in which the story is set. This in turn means that the idea and its implications are important to the structure of the story e.g. the plot will take them into account, the world backdrop will include them and occasionally get “screen time”, etc. The idea itself can be mundane or tried-and-true – what if we really did never have to die? – but someone will have seriously thought about what it means. That’s not imagination, that’s scholarship … or craftsmanship … or science. It’s the difference between concept and execution, of prototype and finished product.

Because a greater importance (in plot, structure, content) is placed on this science and backdrop, this in turn means that less importance will be placed on other elements – generally including characters, but not necessarily. (I tend to like hard SF stories where the extrapolation of the idea leads to character dilemma, hard decisions, and growth e.g. What does it mean to be human in a world where androids are becoming smarter and smarter, and demonstrating true emotional complexity?)

This means that a lot of hard SF can be confused with shallow stories with SF trappings e.g. the worst of Star Trek or Doctor Who, where technobabble saves the day on a regular basis. On the other hand, some of my favorite episodes could have been lifted and plunked down in a historical setting with very little change at all, because it was about the characters, not the ray guns or time travel.

Rigorously exploring the implications of an idea is, unfortunately, an easy road to pedantry, lecturing and boring storytelling. There’s a David Brin book centered around one idea – what happens if people could change sex, but only once? – and the central characters play out their decision on a voyage around the world. The idea and its implications are explored in extreme depth, and there are lots of fascinating segments, but the whole novel is l-oooooooo-ng and hard to read.

As far as the “fun” factor, one of my favorite 20 minutes of Star Trek TNG is the middle of “Brothers”, where Data receives a coded signal to come meet his maker (literally) and proceeds to single-handedly hijack the Enterprise, making efficient and logical use of his abilities. This is a hard SF sequence – it’s all about the implications of Data being an android – and very enjoyable, at least for me.

Anyway, it’s probably all moot, but it seemed a shame to waste all the time I spent thinking about it in my misspent youth :<)