Further to my previous post, I'm having one of those kinds of days - i.e., of the kind represented by this image. It seems illogical to go very deeply into the history of science fiction without first offering some sort of account of what it actually is. But of course, it is notoriously difficult to define, and all definitions are controversial. Just why is very difficult to explain to someone who lacks a fairly detailed knowledge of the history of the field. This seems like a catch-22 situation. In the more leisurely space of a book, it would be possible to deal with it by writing chapters that tackle the problems from different angles. That's not possible in a relatively short article.
I suspect the solution will eventually involve writing something much simpler than I'd really like.