Here’s Cory Doctorow taking a stab at the (always somewhat risky) business of defining science fiction, in the context of a plug for Neal Stephenson’s newest:

Science fiction isn’t collection of tropes, nor is it a literary style, nor is it a marketing category. It can encompass all of these, but what sf really is, is an outlook.

At the core of sf is an approach to technology (and, sometimes, science): sf treats technology as a kind of crux that the rest of the tale revolves around. The Bechdel test invites us to notice that in most fiction, stories revolve around men – that it’s rare for two or more non-male characters to interact with one another, and if they do, that interaction is triggered by a man.

The sftnal version of this would go something like this: “a story gets increasingly stfnal to the extent that interactions among characters either directly relate to a technology, or are triggered by the consequences of such a relation, or fears, plans or aspirations for same.”

(Note that this implies that science fiction is a spectrum: things can be more or less science fictional, and that gradient reflects the centrality of a technology to the narrative.)

Noting this here as a mainstreaming of a theory of sf first codified as an “evaporated genre” by the eternally affable Gary K Wolfe, which I myself have tended to bastardise by saying something along the lines of sf not being a thing that a text is or is not, but rather a thing in which a text may (or may not) partake to a greater or lesser degree.

(Of course, somewhat contra to Cory above, sf is also still very much a marketing category—which is why it’s a site of clashes over identity politics, because we’re still very much stuck in a paradigm where we think of ourselves as being defined by what we consume.)

I would personally also prefer to come at the question in terms of the sociotechnical, having spent far too much time thinking about the problematics of an episteme that considers “technology” to be ontologically distinct from the social conditions of its design, production, use and disposal… but then Cory, gawd bless him, writes like a man whose aim is to make things simpler for the reader, rather than more complicated.