It might be a rare occasion (perhaps at a party) when someone finds out that you’re writing a book and asks you ‘What’s it about?’ — but when they do, what do you say?
Do you immediately launch into setting a scene and then describing the progress of a character or group of characters through it?
Do you try to describe your lead character and his or her quandary?
Do you go abstract and tell them the theme of the tale, like ‘Prejudice’ or ‘Death’, and leave it at that?
Or is it so difficult to answer that you reply ‘Writing a book? Who told you that nonsense?’ and change the subject?
Being asked a direct question like ‘What is your book about?’ could be viewed as your first marketing test as an author.
It’s also a test of how well you really understand what you are doing — which underpins any successful marketing later.
What you could really do with is a premise — defined in the dictionary as ‘an assertion or proposition which forms the basis for a work or theory’ but used in fiction writing to mean, as James N. Frey says, the single statement ‘of what happens to the characters as a result of the actions of a story.’
For example, the premise of The Lord of the Rings (and a huge number of other similar epics) might be that ‘pride leads to destruction, while self-sacrifice leads to wisdom.’ Not ‘a hobbit is sent on a quest to destroy a magic ring which has the power to rule the world’. (Note: some writing guides will tell you that the latter is the premise, but if you can go deeper, it’s never the premise.)
Every story has a premise.
To go even further, every successful story has only one premise.
It is the underlying idea of your story, the foundation which underpins the plot and determines what the characters actually do and how they evolve.
If you can work out what your story premise is, it will not only become easier to write the thing but easier to explain it in simple terms to others. That will make marketing much easier later.
Having a premise is like flicking lights on in a dark room: things which you struggled to grasp before suddenly become clear. Your plot will fall into place; your characters will be driven forward.
Having a clearly expressed premise will prevent you from wandering too far from your theme and define the beginning, middle and end of your plot.
Premises tend to express universal truths. They are not statements of mystery or esoteric ideas: ‘Pride comes before a fall’ is another way of stating the premise for The Lord of the Rings, for example. It turns out that the same ‘pride’ premise underpins everything from Star Wars to Great Expectations, from the Marvel Cinematic Universe films to your favourite TV soap opera. Nothing wrong with that — often the simpler and more familiar a premise is, the more powerful a story can be. Even the most literary novels have simple premises: War and Peace, for example, has a similar ‘pride’ premise to those tales listed above: Napoleon’s 1812 invasion of Russia and all the chaos and adventure and tragedy that that brings turns out to be a metaphor for the effects of pride.
You’re not trying to be creative when devising a premise, really. The most obvious premises are the best: ‘Love triumphs over all’, ‘You get out what you put in’, ‘Good guys always get the girl’ are examples.
Where do you go from there? Is your premise what you say to anyone who asks you what your book's about? Not quite.