Will it run, or fly?

Ideas are the life-blood of SF.  And we often get them by asking the magic question "what if?"  But every writer knows that ideas don't make a story.  They're only the first stage in the process of turning that creative spark into a fully-fashioned narrative,

It helps to know at an early stage whether our idea will run - or more likely, fly if it's an SF story.  And that means examining and questioning the idea in detail before we start writing.

Is the idea logical?  Something that totally reverses known science had better be well worked-out and justified before you start to write it.  If there's no evolution by natural selection on your world you have to show in detail what other mechanisms are at work there.  Of course, your book could be based around this new scientific discovery and how the knowledge changes science.

Coming up with original ideas is also a challenge.  At this stage in the development of SF, many ideas are re-workings of concepts that are well accepted into a different form.  But that doesn't mean you can't produce something stunning.  Witness the ancillaries in Ann Leckie's Ancillary Justice.  It's about adapting or modifying what's gone before.

I did exactly that with my novel Eyemind.  I love Anne McCaffrey's brainship books, and I wanted to do my own take on them.  So I created Bi, a paraplegic housed in a Supercruiser who works for Intel.  The basic idea is shamelessly copied from Anne McCaffrey, but I've put my own stamp on it.  Bi controls a land vehicle not a starship or space station, and he's basically working as a PI.

If you're writing a novel you've got to be sure that your idea will sustain a long narrative.  That means you'd be wise to work out its details and some idea of the plot before you start writing.  Working out the science, culture, and politics surrounding your idea will give weight to it, and you confidence that you can pull the story off.

One of the criticisms I have of so-called Golden Age SF stories is that they're all idea, they're all shiny tech.  Often that tech was worked out in detail and lovingly described, but what wasn't described was its effect on the societies that used it.  How do instant ansible communications change societies?  How do people feel emotionally about the tech?  Will it prompt New Luddites out into the city's streets to destroy this evil creation?

Deciding whether an idea will fly is about knowing how it drives the action of the story, and how it affects the motivations of the main characters.  You've got to get these things in place or your idea won't fly.